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Discussion of Problems Related to Hormonal Factors in Initiating and Maintaining Tumor Growth* JACOBFURTH (Children's Cancer Research Foundation, Children's Medical Center, Cancer Research Inst., New England Deaconess Hospital, and the Dept. of Pathology, Harvard Medical School, Boston, ilass.) It is a gigantic task to evaluate the mass of re ported data and opinions well assembled by Drs. Kirschbaum and Hertz and to point to avenues which future research may profitably explore. No building is solid that rests on crumbling material or is loosely constructed. My first task is to ex amine the assembled information. I trust that the critical comments directed at vulnerable points shall not obscure the wealth of ideas cited and ex pressed by the preceding speakers, which I shall not underline. Challenge is intended merely to test the solidity of some observations cited. Dr. Gardner will, I believe, agree with my quali fication of his introductory words that endocrine neoplasia represents but a small segment of the cancer problem. If by hormones we mean humoral influences, specifically regulating the growth of many if not all cells, hormonal tumorigenesis is a key subject in cancer research. However, aside from this, a large percentage of human tumors oc curs either in endocrine organs or in their target cells. Evolution of cancer. Dependent and autonomous variant^.—The greatest contribution of research in endocrines is, in my opinion, the establishment of models pointing to the sequence of transforma tion from normal to dependent, and from the latter to highly autonomous tumor cells, and leading us to a useful concept on the fundamental nature of the neoplastic state. It is a universal belief that the tumor is an ab normal mass of tissue which persists after cessation of stimuli which evoked it. Research in endocrine neoplasia taught us that this definition is errone ous—that cancers or tumors are a state in which cells proliferate with limited or with no restraint in a complex system of cells, either because of a change in a physiologic mechanism limiting the number of that cell type or because of an alteration * Presented at the second meeting of the Scientific Review Committee of the American Cancer Society, held at the Westehester Country Club, Rye, New York, December 13 and 14, 1956. in cells resulting in failure of responsiveness to the physiologic forces. The former type of neoplasm or tumor is called dependent, the latter autonomous. Both can metastasize. Dependent tumors can be arrested by restoring to normal the specific regula tory mechanism which was disturbed. The sequence of changes from a normal cell to an autonomous neo plasm as sketched in Chart 1 is common among the EVOLUTION OP CANCERS Sequence of changes, to changeInhormonesCorrection NORMAL cell »hyperplasiaDEPENDENT can hostIncellResponsiveness be completeGrowth T* AUTONOMOUS T responsive,J, highly less and less responsive \ reversely responsiveBasic full autonomy can be retardedbut not arrested None CHART1.—Schemeof the sequence of changes induced by derangement of physiological forces regulating cell growth, which can result in evolution of cancer cells from normal cells. From Ref. l, Cancer, 1957, in press. endocrine organs, but the autonomous tumor can also arise without an intermediate dependent phase. The core of the cancer problem is not merely that of detecting forces which bring about a per manent modification of a normal cell, e.g., a mutagen, but also the forces which create a state which allows one cell type to proliferate, uncontrolled, in a system whereby the number of each of hundreds of different kinds of cells is limited by a specific mechanism. This neoplastic state can be brought about by any disturbance which interferes with the homeostatic forces specifically limiting the 454 Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. FuRTH—Hormonal Factors and Tumor Growth number of each cell type. The general problem is, therefore, that of the cancerous or neoplastic state. One major specific problem is the origin of the autonomous cell. Another major problem is the origin of a dependent tumor, and this is an endo crinologie problem par excellance; in the develop ment of cell autonomy, endocrines may play a mere preparatory role. Chart 2 is an over-simplified sketch showing the servo-mechanism which maintains the cell level. Unrestrained proliferation of a cell, here desig nated as target cell, can be brought about (a) by excessive stimulation, (6) by lack of the restraining force, and (c) by altered responsiveness of either the target or the regulating cell, resulting in an ex cess of the stimulating factor ("hormonal imbal ance")- This, too, is an oversimplification of the situation. Arrows in the sketch indicate that both regulator and target cell and each force (hor- SCHEME OF FEED-BACK REGULATION CHART2.—Sketch of feed-back type of growth regulation pointing to stimulatory and retarding (push and pull) forces. mones, etc.) are subject to promoting and retard ing influences. The following are simple examples that are well proved experimentally. a) Examples of induction of tumor by exces sive, sustained stimulation: Large quantities of estrogenic hormones stimulate to progressive pro liferation one cell type of the pituitary, to be called the mammotrope. Many of these mammotropic tumors will not grow on a normal host but pro liferate with no apparent restraint in hosts treated with excessive quantities of an estrogen (10). If this stimulation is not interrupted, dependent tumors may give rise to autonomous variants. There is a direct quantitative relationship between the estro gen administered and the rate of proliferation of mammotropes (5). The induction of pituitary tu mors by estrogens has been demonstrated in mice, 455 rats, and hamsters, but only in the former two spe cies has it thus far been shown that these tumors are mammotropic. Similar examples are the induction of Leydig-cell tumors with estrogen and of ovarian tumor by gonadotropins. The latter is achieved by grafting ovaries in the spleen of castrates. All tu mors so induced appear to be at first dependent but have a strong tendency to give rise to au tonomous variants. b) A good example of tumor production by de ficiency of the specific restraining force is that of thyrotropic pituitary tumors by lack of thyroid hormone. Almost every mouse of every strain thus far tested will develop a thyrotropic pituitary tu mor. Tumor induction can be stopped by adminis tration of thyroid hormone. It can be said for a first approximation that this exemplifies how lack of an inhibitor can cause tumor development. The mechanism by which lack of thyroid hormone causes proliferation of thyrotropes is, however, far more complex. c) Lack of responsiveness of a target cell, the third type of derangement, is probably the most common and certainly the most important one. Good examples are tumors induced by ionizing radiation and mutagenic chemicals; e.g., ovarian tumors are induced by ionizing radiation in al most every female mouse. If a threshold dose of about 30 r whole-body radiation is exceeded, in time almost every female mouse will devel op an ovarian tumor. Ovarian irradiation alone will also induce such tumors. The irradiated ova ries are injured but not destroyed. Irradiated animals can become pregnant, but after a few pregnancies they become sterile, and after about a year and a half they will develop ovarian tumors. Conclusive evidence for the role of gonadotropic hormones in the induction mechanism of these tu mors has been reviewed by Dr. Kirschbaum. Ir radiated ovaries secrete gonadal hormones, but, apparently, the feed-back mechanism of gonadalgonadotropic hormones is so disturbed by irradia tion that the balance is tilted to a sustained overstimulation of granulosa and lutein cells of the ovary, leading to tumor development. Irradiation of ovaries before transplantation into the spleen of gonadectomized rats resulted in the development of larger tumors (Kullander [13]), indicating fur ther that irradiation induces some change in ovari an cells, disturbing but not abolishing their respon siveness to gonad-stimulating hormones. A variant of the first two possibilities is tumor induction by metabolic antagonists. A good ex ample is the induction of thyroid and pituitary tu mors by long-continued administration of antithyroidal compounds. In thyroid tumorigenesis by Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. 456 Cancer Research thiouracil the sequence of changes from normal cell to dependent and from dependent to autono mous tumors has been thoroughly studied. This sequence of events has been fully described else where (9). Charts 3 and 4 are schematic diagrams illustrating the behavior of dependent and autono mous tumors in variously conditioned hosts. The time required for transformation of depend ent to autonomous tumor cells varies with differ ent types of tumors and is characteristic for each, although there are great individual variations. For example, in the case of thyrotropes, acquisition of DEPENDENT TUMOR cells were dependent. Tumors recurring after simi lar treatment, and in the absence of excretion of androgen metabolites, can be supposed to be au tonomous. Acquired reverse responsiveness, an important event from theoretical and practical standpoints, has not been adequately studied. Animal experiments are not immediately ap plicable to man but should be looked upon as models to explain events in humans and as tools to test hypotheses on stimulating and restraining forces of cells (both normal and neoplastic) and as tools in the search for antagonists of hormonally responsive tumors. Is the neoplastic change sudden or gradual? With thyrotropes, dependent tumors arise in dis tinct loci ("micro-tumors")- Are these already al tered but still fully responsive beta cells? Acquisi tion of autonomy appears to be gradual and pro gressive in severity. Yet, this may not be so. Cur rent observations relate to populations of cells the IN »EU.CONDITIONEDHOST MODIFICATIONOF TUMOR GROWTH BY CORRECTIONOF FEED-BACK DISTURBANCE ACCELERATION OF GROWTH CHART3.—Schemeof the relative growth rate of depend ent tumors in different hosts. TUMOR AUTONOMOUS. REVERSEUr RESPONSIVE PROGRESSIVE -TUMOR GROWTH' AUTONOMOUS. NONRESPONSIVE. .RETARDATION OF GROWTH TUMOR AUTONOMOUS AUTONOMOUS NON-RESPONSIVE UIMOR TUMORS BOT RESPONSIVE. RESPONSIVETUMOR REGRESSION TUMOR FUU.Y DEPENDENT K NORM«.HOST CHART5.—Scheme of modification of response of tumor growth by attempted correction of a feed-back disturbance. CHART4.—Schemeof the relative growth rates of respon sive and nonresponsive autonomous tumors in different hosts. autonomy has not been noted in the original host and first passage, while with mammotropes it is usual in the first passage. With both testicular and ovarian tumors, autonomous variants commonly arise in the original hosts. Chart 5 is a diagrammatic illustration of how tu mor growth is modified by therapeutic application of its presumed physiologic regulator. The rare cases of prostatic carcinoma, described by Huggins, in which regression was permanent following operative removal of the source of androgens, could be explained by supposing that all tumor composition of which is influenced by host factors and changes with time. Mammotropic tumors ap pear in diffuse hyperplasia, and no borderline is known between hyperplasia and dependent neo plasia. Conclusive answers will not be forthcoming until the progeny of different cells can be followed, as has been done with mammalian cells with the use of ascites and tissue culture technics. Current nomenclature is inadequate to desig nate the various types of autonomous and depend ent tumors. The term malignancy is currently used to express autonomy, but autonomous tumors can be highly responsive. Metastasis is considered in dicative of autonomy, but dependent tumors can also metastasize by both the blood and lymph stream, and they can invade adjacent structures by continuity. The difference is merely quantita tive. Dependent tumors are progressive in, and fatal to, conditioned hosts. Many benign tumors Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. FÃœRTH—Hormonal Factors and Tumor Groivth are probably conditioned growth disturbances (Bungeler [3]). \Vhere is the borderline between hyperplasia and dependent neoplasia? Withdrawal of the stim ulus will correct both. The difference lies in the host. In hyperplasia the disturbance in homeostasis of cell numbers is temporary, and the balance is ultimately restored. In dependent neoplasia the disturbance is lasting. Conceivably, a dependent tumor is an uncompensated hyperplasia. Parallel comparative investigations (biological, morpho logical, and biochemical) on hyperplastic, depend ent, and autonomous tumor cells derived from the same normal cell are much wanted for understand ing the basic differences among them. Pituitary tumors.—I shall now discuss experi mental pituitary tumorigenesis because of its unu sual research potentialities : (a) there is the possi bility of biologic dissection of the pituitary into its morphologic units; (6) to obtain monomorphous tropic hormone-secreting cells for isolation of hor mones and for morphologic and physiologic char acterization of functional units of the pituitary; (c) to provide systems for investigations on dis turbance in feed-back mechanisms; (d) to follow the transformation of normal cells to fully depend ent tumor cells and these into autonomous but highly responsive tumor cells, and the latter into fully autonomous cells. With some pituitary tumors, such as those of thyrotropes, tumor induction and transformation occur slowly, so that each type of neoplasm can be fixed in the frozen state, and later all can be recovered and examined under identical environ mental conditions. Biochemical efforts thus far have failed to elucidate the basic neoplastic change, as we learned from the proceedings of the last conference of the Scientific Review Committee of the American Cancer Society (17). The theory of Warburg is negated by Weinhouse and others, and Greenstein's review indicates that no specific enzymatic or other biochemical differences have been discovered which would clearly distinguish a cancer cell from a normal cell. The availability of dependent and autonomous neoplasms should en courage chemists to renew their efforts under more favorable conditions than was done earlier. Although histologists consider the pituitary as a mosaic of well differentiated, differently function ing cell types, in the cancer literature pituitary tu mors are lumped together without clear characteri zation of the tumor cell. Our reviewers give too much credence to work which ignores the specific character of pituitary tumors induced by diverse procedures without ever assaying any tumor, and 457 too little credence to the existence of monomor phous pituitary tumors of diverse types. Three distinct pituitary tumor types are avail able in our laboratory: thyrotropic, mammo tropic, and adrenotropic. These can be readily induced, and several strains of each type have been exten sively studied. Their distinctness is clearly indi cated in hypophysectomized hosts. Transplanta tion assays are essential to characterize them, since the secondary changes in primary hosts do not disclose with certainty the identity of the tropic tumor; e.g., primary thyrotropic tumors can occur either with enlarged (but hypofunctional) or with an atrophie thyroid gland. Secondary and tertiary changes often obscure the basic event; e.g., thyrotropes invariably have a trace of gonadotropic activity (2), but, given time, the estro gen overproduction from stimulated ovaries will, in turn, stimulate the mammotropes and these the mammary gland. The latter change is blocked by hypophysectomy of tumor-bearing hosts, but not the former (unpublished data with Clifton). Mammotropic tumors were induced in our labo ratory by two procedures: (a) stilbestrol pellets and (6) ionizing radiations (11). Prof. Lacassagne, who is with us today, was perhaps the first to indi cate pituitary tumor induction by estrogens. Others, including Dr. Gardner, followed him closely. The attractive assumption that the two procedures have a common denominator, namely estrogen excess, remains to be proved. Some pitui tary tumors induced by Woolley et al. by gonadectomy at birth may also be of this type, since gonadectomy in their strain causes gonadal hor mone-secreting adrenal tumors. Mammary gland hyperplasia in mice bearing such tumors was men tioned by Dickie and Woolley. This is also a sec ondary change with thyrotropes. Our observations (10) suggested that a major force in the induction of mammary tumors with estrogens is the mammotrope. The literature on the hormonal genesis of mammary tumors has been recently reviewed by Milhlbock in Advances in Cancer Research (15) without mentioning the mammotrope and its hor mone. However, now that the picture of mammo tropes clearly emerges, older observations can be re-interpreted as favoring this view; e.g., pituitary grafts outside the cranial cavity cause mammary tumors, presumably by virtue of surviving func tional mammotropes (luteotropes, Mühlbock). Hypophysectomy of estrogen-treated mice will prevent mammary tumor development (Gard ner).1 The possible significance of mammotropes in 1Symposium of the American Cancer Society on Endocrines and Cancer, October, 1956. Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. 458 Cancer Research causing human tumors has been recognized by Hadfield (12), whose efforts are directed to assay this hormone in a mammal. The usual assay in pigeons that measures secretion (hence, the name prolactin) may not be a true measure of this tropic hormone. Adrenotropic tumors can be induced by totalbody ionizing radiation. Their induction mecha nism is yet to be worked out. Current experiments (with Buffett) indicate that head irradiation alone will induce them, but not adrenal irradiation or adrenal-gonadectomy. The current view that the pituitary is a radioresistant organ is due to failure to observe the animals over sufficiently long periods of time. The latency period of this tumor is more than half the lifespan of the animal. Whether or not this applies to man remains to be seen. I recall Dr. E. Shorr de nying the carcinogenicity of estrogens in man, now amply documented by the references cited by Dr. Hertz. The remarkable specific features and side effects of these three types of tropic tumors have been de scribed elsewhere (see 9). The mammotropes have a "built-in" somatotropic effect. The mouse adrenotropes do not have any other manifestations than those resulting from adrenal hyperfunction, but assays of Steelman (16) have shown that they possess a marked melanotropic activity. The thyrotropes have some gonadotropic effects and cause dilation of the extrahepatic biliary tracts. These findings on the existence of three distinct types of pituitary tumors should encourage re search on induction of monomorphous pituitary tumors of all other pituitary cell types. The exist ence of a folliculotrope and of a luteotrope is gen erally accepted; if this is true, they too should yield monomorphous tumors. The growth hormone is of special interest in can cer research. Is there a specific somatotrope? Per haps the acromegaly syndrome is due to a tumor of somatotropes. The possible existence of a soma totropic tumor in mice is suggested by our frag mentary observations (9). Three tropic cells have distinct general growth-promoting effects: the mammotropes, apparently by direct effect of the hormones they secrete; the thyrotropes, by way of thyroid hormone (TH) production; and gonadotropes, by way of androgen production. The spe cific differences in growth promotion by these hor mones remain to be fully analyzed. Dr. Kirschbaum raised the question as to the induction mechanism of somatotropic tumors. I have no conception (and have heard of none) con cerning the homeostatic mechanism of growth hormone secretion. The growth-promoting tropic tumors studied by us are linked to mammotropes, and estrogen is their stimulant. As mentioned ear lier, two other tropic hormones (thyrotropins and gonadotropins) have indirect somatotropic effects. The existence of a somatotrope distinct from that of the mammotrope is being postulated on the basis of chemical isolation of such a hormone. It is also related to acidophils which are conceivably distinct from the mammotrope. Growth hormone is an anabolic hormone, related to protein, nucleoprotein, and carbohydrate metabolism, and its homeostasis may somehow be linked to these proc esses. In the following, I shall comment more spe cifically on papers reviewed by Dr. Kirschbaum. In the induction of pituitary tumors by Im (and by other means), the view of Gorbman and Edelmann is cited, who attribute an essential role to such nonspecific events as stress. Investigations reviewed by us elsewhere indicate that these tu mors are thyrotropic and that any of four proce dures will induce such tumors: radiothyroidectomy, surgical thyroidectomy, antithyroidal com pounds, and iodine deficiency. Obviously, the common denominator of these procedures is lack of TH. Complete surgical thyroidectomy in mice is a very difficult procedure and is seldom completely successful. A few cells left behind and ectopie cells will undergo compensatory hyperplasia. Radiothyroidectomy, on the contrary, can reach all cells. If a few cells are left undestroyed, they do not proliferate, probably because of radiation fibrosis and vascular stenosis. Noting that Gorbman and Edelmann's idea that radiation is essential to induce tumors by I131 met with wide acceptance, I should like to present a simplified tabulation of our relevant work, indi cating the contrary. Table 1 shows that the thresh old tumorigenic dose is about 25 pc. of I131in fe male, and about 50 /ic. in male mice. Following this background information, the borderline dose of 30 (ic. was selected for the study of the possible en hancing effect of radiation on induction of thyro tropic tumors by I131. Table 2 shows that the incidence of tumors was about the same in all females, but in the x-radiated group more reached a macroscopic size. Monthly tabulation of the pituitary changes after radiothyroidectomy indicates that whether an animal has a macroscopic tumor or a microtumor depends entirely on the time when the animal dies after I131 treatment. The succession of events seems inevi table: most, if not all, thyroidectomized animals Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. FTJRTH—Hormonal Factors and Tumor Growth that live long develop a macroscopic tumor. As Table 2 indicates, 94 per cent of the female mice given 30 juc.alone had pituitary tumors (including microtumors), as compared with 84 per cent of mice given 30 /¿c. and irradiated over various parts of the body. However, more of the animals receiv ing the added irradiation had macroscopic tumors. In the same experiment, no tumors were produced in males by the combined treatment. Thus, added radiation may have hastened tumor growth but did not increase the tumor incidence or lower the threshold in males. The surgical thyroidectomy experiments (Table 3) indicate conclusively the unessentiality of radia tion. In the first series the animals which were op erated upon received 5-9 juc. of I131(one or two doses), to test the completeness of thyroidectomy. 459 In the second experiment, no I131was given. The operations were not so successful in the second se ries as in the first. Many mice had regenerated thyroid tissue. Nevertheless, 15 per cent had mac roscopic tumors, and 57 per cent had microscopic tumors. Thus, there is no evidence to support the sug gestion of Gorbman that nonspecific stress is a ma jor factor in induction of pituitary tumors by I13'. This investigator did not assay the tropic features of these tumors. The radiation-induced tumors studied in two large series were generally adrenotropic or mammotropic, and without thyrotropic activity. The ideas of Gorbman (1956) completely ignore the specific features of pituitary tumors in duced by different procedures. We failed to find published data supporting the statement that TABLE1 RELATION OFQUANTITY OFI"1 TOINDUCTION OFPITUITARY TUMORS IN MICE FEUALES im(MC.)2550100-200Totalno*22343—562±640 Total MALES Tumors* Total no. 16 Groas 0 13 ± 3 Tumors* Total Gross 0 (45 per cent) ( 5 per cent) 13 9 13 22 6 3 (57 per cent) (39 per cent) (59 per cent) 32 22 4Ãœ 2 34 4 (75 per cent) (51 per cent) (85 per cent) —¿ = no tumor; ±= thyroidectomy changes. FT* "Gross" indicates replacement of the pituitary with a macroscopically identifiable pituitary tumor. "Total" microscopically detected tumors in enlarged pituitaries. 9 (41 per cent) 27 (67 per cent) includes the TABLE 2 THE EFFECTOFADDEDX-RADIATIONONTHYROTROPIC TUMORINDUCTIONBYI111IN MICE* FEMALESNo. MALM No. ingroup17152121192:¡Per in centTotal94867686890tumorsGross18S3284847Per Per cent tumors centnegative614341411100 Per cent No. in Per cent TREATMENT I'« 30 MC. " " X-ray group 17 Total 94 Gross 18 negative 6 500 r totalf 500 r upperf 500 r low-erf 50 r total group 6 9 2 negative 100 100 100 100 100 500 r total * Survey 240—408days after thyroidectomy. t Total-body, upper and lower half (approximate) irradiations, respectively. nitrogen mustard is a co-carcinogen in pituitary tumorigenesis. There is ample evidence indicating INDUCTION OFPITUITARY TUMORS BY SURGICAL THYROIDECTOMY* that, in general, ionizing radiations arc powerful co-carcinogens, and, conceivably, they alone can 150-299431011DATS300-3996141312400-409151410103Õ2 EM. induce a tumorigenic change in every type of No. in group I pituitary cell; but in the induction of thyrotropic 0 and ± pituitary tumors by I131,they appear to play an Microtumor Gross tumor insignificant role, if any at all. The pituitary tumors found in gonadectomized II No. in group 0 and ± mice, to our knowledge, have not been adequately Microtumor assayed. They were not transplanted in series. Gross tumor * Simplified retabulation of data published earlier. Changes in the original host, e.g., mammary gland TABLE 3 Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. 460 Cancer Research stimulation, do not prove the mammotropic char acter of the tumor (witness the situation with thyrotropes already cited). On theoretical grounds, one can presume that these tumors are either gonadotropic or mammotropic. If lack of gonadal hormone is sustained, the former is expected. If compensating gonadal hormone secretion by the adrenals goes on unchecked, the latter is expected. The original observations (with Upton) on radiation-induced pituitary tumors were made in an experiment on the late effects of an atomic explo sion ("Operation Greenhouse"). The exposed mice were LAFi hybrids, the irradiation high energy gammas with some neutrons, and the exposure was over the entire body. Of ten such radiation-in duced tumors that were assayed, three were adrenotropic, six were mammo-somatotropic as de scribed, and one was atypical with predominantly somatotropic effect (9). In a current large-scale study on the pathogenesis of these tumors,2 pituitary tumors occurred thus far only in the nonirradiated parental L strain and none in normal A and LAFi mice. Whole-body x-radiation induced them in all three strains. In LAFi mice, 500 r over the head (pitui tary?) also induced pituitary tumors, but not 400750 r over the abdomen, including the adrenals. Adrenalectomy did not enhance the tumor induc tion rate by whole-body irradiation. These findings were contrary to expectations. Furthermore, 500 r x-rays over the head appears to be as tumorigenic as total-body irradiation by a similar dose. Numerous tumors of the recent series are being assayed, and the first four proved to be adrenotropic, as were those of "Operation Greenhouse" series. All radiation-induced tumors proved to be autonomous but highly responsive. Growth of the adrenotropes is enhanced by adrenalectomy; growth of the mammotropes is enhanced by estro gens and counteracted by androgens. The second ary changes to adrenotropic tumors (marked obes ity, thymic involution, lymphopenia, polyuria, polydipsia, and extraordinary sensitivity to infec tions) are evident with the new strains. Main tenance of these strains necessitates adrenalec tomy or uninterrupted administration of anti biotics. Adrenalectomy promptly counteracts all secondary changes and enhances tumor growth. The main hormone secreted by the stimulated adrenals has been identified by Hildegard Wilson and associates (1) to be corticosterone, which is the predominant corticoid of the murine adrenal. In animals receiving 1,250 r or more, there is, as a late 2J. Furth, R. F. Buffett, and E. L. Gadsden. On the Pathogenesis of Pituitary Tumor Induction by Ionizing Radiation (in preparation). effect, a marked atrophy of the pituitary gland with secondary atrophy of its target organs. These experiments urge caution in using irradiation for depression of the pituitary. Induction of thyrotropic tumors by total-body ionizing radiation, like those developing following thyroidectomy, has thus far not been reported. We described a primarily somatotropic strain with some thyrotropic properties (9). Recently, two thyrotropic tumor strains were isolated in our laboratories. One occurred in a DBA mouse that received whole-body 475 r, the other in a headirradiated LAFi mouse. Both had features of au tonomous thyrotropic tumors indistinguishable from those originating in radiothyroidectomized mice, possessing, as the latter do, gonad-stimulating properties. Thyrotropic tumors can occur spon taneously (Bielschowsky), and possibly these were spontaneous cases. On the other hand, radiation can enhance the likelihood of a neoplastic change in every irradiated cell. The latter is well exempli fied by ovarian tumorigenesis by ionizing radia tion. It has been possible to isolate from irradiated ovaries tumors of every cell type of the ovary. Since head (pituitary?)3 irradiation alone can in duce pituitary tumors, it is possible that, with per sistence and added specific stimuli, tumor strains can be developed from every tropic cell type. With respect to thyroid tumors, the evidence is strong that low iodine intake or antithyroidal com pounds are tumorigenic in almost every species, including man, and that the sequence of events is : decrease in TH, secondary increase in thyroidstimulating hormone (TSH), followed by stimula tion of the thyroid. The latter is, at first, diffuse; later, it is nodular. It is also certain that this adenomatoid hyperplasia has some tendency to give rise to carcinomas. Consequently, the idea (Astwood) of using, in such cases, thyroid hor mone for depression of TSH production is well founded. With respect to induction of thyroid neoplasms by I131,the only reported observations are those of Chaikoff, published in 1951. Numerous investiga tors have since attempted to induce thyroid tu mors by I1'1 but with no success. In a recent larger series, Lindsay, Potter, and Chaikoff (14) found that the incidence of spontaneous thyroid tumors (alveolar carcinomas) in Long-Evans strain rats that were given small doses of I131 (10 and 25 pc.) was approximately the same as that in control rats. However, in addition to the alveolar carcino mas, they found benign thyroid adenomas and follicular and papillary carcinomas in rats that *The question mark after pituitary hints at the unexplored role of the hypothalamus in pituitary tumorigenesis. Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. FuKTH—Hormonal Factors and Tumor Growth 461 had been given injections of 10-100 juc. I131.The ample of tumorigenesis based primarily on an al incidence of all types of thyroid tumors was de tered responsiveness of the target organ. pressed in rats that had received 200 and 400 ¿ic. Virtually every cell of the ovary can give rise to of I131. a neoplasm. Likewise, there can arise in a single ovary, singly or in combination, granulosa-cell tu With respect to the hazards in humans, patients mors, luteomas, tubular adenomas, theca-like tu with three diseases are being given conceivably tumorigenic quantities of I131: hypertension, mors, hemangio-endotheliomas, and sarcomas. exophthalmos, and thyroid carcinoma. In a survey While the Yale workers (Dr. Kirschbaum is one of of thousands of cases at a recent conference at the them) concentrated on problems related to the pathogenesis of ovarian tumors, we proceeded to Argonne Cancer Hospital, no evidence was pre sented suggesting that I131causes thyroid cancers study the character of the tumors induced in the in man. The total-body ionizing irradiation inci ovary by ionizing irradiation. It was noted that dental to I131therapy is, however, within the leu- pure lines of functional granulosa-cell tumors were kemogenic range, and several cases (about five or almost invariably associated with hypervolemia, six) of leukemias have been reported in I131-treated the degree of which paralleled evidence of estrogen patients. All were myeloid and occurred within a secretion. The luteomas, on the other hand, were few years after treatment. In my evaluation, the associated with masculinization and profound sum total of these reports strongly suggests that atrophy of the adrenal cortex. This raised the these leukemias were induced by I131,but others question whether the lutein cell secretes one or doubt this. Should it be necessary to give such several types of hormones including corticoids. large doses of radioiodine to patients who do not Neutralization tests (with Kahn) suggested more than a thousand-fold increase of ovarian hormonal have bone marrow métastases,one should con sider preserving in deep-freeze some of the pa secretion by grafted autonomous and somewhat tient's marrow before treatment and re-introduc responsive induced ovarian tumors. Recent work ing it into the same patient after treatment. It has on corticosteroidal tumorigenesis now clearly indi been shown that the hazards of leukemia induction cates the role of progesterone in the pathway of by irradiation are markedly diminished by bone adrenal cortical hormones and points to simple in vitro studies to resolve this problem. It is desirable marrow infusion. With respect to experimental leukemogenesis by to study further pure lines of these hormonalI181, observations made with Burnett at Oak secreting ovarian tumors of various types, to iden Ridge have shown that, when the thyroid is par tify their secretions, and to test them in vitro for tially destroyed, the total-body retention of I131is steroid hormonal genesis and responsiveness to greatly enhanced. Consequently, I131,if given in gonadotropic hormones. fractionated doses, will deliver a greater totalHow is ovarian tumorigenesis by gonadotropins explained in cells which are not known to be horbody irradiation than if given in a single dose. The development of thyroid tumors in children monally responsive? If excessive gonadotropins who received therapeutic irradiation for large alone are the cause of these ovarian tumors, why thymuses and lymph nodes several years after ir isn't there a cutback of gonadotropins by the radiation has been reported (Simpson and Hempel- gonadal hormones secreted by these tumors? It mann, see 8). There are no experiments on record can be supposed, therefore, that disorganization of indicating that direct irradiation of the thyroid is the ovary by irradiation and altered responsive carcinogenic to thyroidal epithelium. However, it ness of the irradiated ovarian cells are major fac is probable that radiation will enhance the likeli tors in this tumorigenesis. The recent work of hood of thyroidal tumorigenesis in people on diets Kullander (13) supports the view that pre-irradialow in iodine or containing antithyroidal com tion of ovaries alters ovarian cells, increasing the likelihood of their tumorigenic transformation, pounds. Experimental ovarian tumorigenesis in mice by while showing also the dependence on gonadotro x-rays does not apply to rats and may not apply to pins of tumors in intrasplenic ovarian grafts in cas man. When it was discovered in 1932 that most x- trated rats. He visualized these grafts by radiogra phy and noted their regression following hypophyrayed mice will develop ovarian tumors, it was as sumed for a first approximation, and in line with sectomy. This is a highly satisfactory technic then current views, that irradiation altered ovari for demonstrating the responsiveness of intra an cells. Subsequent experiments, mainly by splenic ovarian grafts and is eminently suited to Gardner et al. and by the Biskinds, pointed to hor the determination of the exact time when these monal imbalance with excessive gonadotropins as grafts acquire autonomy. Will ovarian tumors so a major factor. Now we believe that this is an ex induced in irradiated ovaries acquire autonomy Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. 462 Cancer Research sooner than those arising in the nonirradiated ovaries? Kullander (13) emphasizes that irradia tion and transplantation of the ovaries into the spleen of castrate animals induces a tumor by a mechanism which is similar to that which is re sponsible for the development of spontaneous tu mors. Spontaneous tumors are likely to arise in ovaries after they undergo atrophy, the latter causing overproduction of pituitary gonadotropins. This appears to be not unique in the domain of endocrine organs; e.g., liver tumors arise most commonly in atrophie cirrhotic livers which are the seat of secondary compensatory hyperplasia. The ovaries of thousands of women have been irradiated, and few, if any, developed such tumors. Since, in mice, abdominal exposure alone is con ducive to ovarian tumor development and since the practice of irradiating ovaries of women dates back several decades, it can be presumed that the high sensitivity of mice to ovarian tumor develop ment is species characteristic. A tremendous amount of published work on ovarian tumors is full of speculations and contra dictions as to interrelationship and function of various cell types. Clearing up this confusion calls for isolation of hormones secreted by different cells, in vitro steroido-genesis by these cells, and visualization of transformation of one cell type into another under well controlled conditions. Theoretically, there are at least five types of adrenocortical tumors: (a) estrogen-secreting, (o) androgen-secreting, (c) glucocorticoid-secreting, (d) mineral corticoid-secreting, (e) nonsecreting, and (/) mixtures of various types. Of these, the existence of only the first two types is indicated by the reviewer. The separateness of estrogen- and androgen-secreting types induced by gonadectomy is suggested by the work of Woolley et al., but the hormones of different cell types have not been identified. The work of Paschkis is cited, showing that these tumors can also secrete corticoids, but the evidence is inadequate; the assay on gluconeogenesis in tumor-bearing animals was carried out in animals with intact pituitaries and adrenals. Transplantable strains of adrenal tumors iso lated recently in our laboratory (in the mouse and the rat) are corticoid-secreting, as indicated by morphologic, hématologie, and urinary excretion studies (7). The in vitro response to ACTH of these cortical tumors was established by Cohen et al. (6). Both tumors responded to as low ACTH levels as 0.1-0.2 mU. Under ACTH stimulation, corti costerone was the major steroid synthesized by the normal mouse adrenal incubates (72 per cent of total A4-3-ketosteroids), and 11/3-hydroxy-A4androstene-3,17-dione was present in small quan tity. Mouse adrenal tumor slices incubated with ACTH produced approximately equal amounts of these two steroids. However, 25-65 per cent of total A4-3-ketosteroids consisted of compounds with Chromatographie behavior suggestive of progesterone, 11/3-hydroxyprogesterone, 11-dehydrocorticosterone, and A4-3-keto-20,21-dihydroxy steroids. Gonadal-secreting adrenal tumors obtained from Dr. Kirschbaum neither secreted corticoids nor responded to ACTH. This is the type of ex perimentation which may shed light upon the con fused subject of morphologic cell type of the adre nal and functions, and gauge responsiveness and function of a given adrenal tumor, thus yielding information applicable to patients' care. Transplantable Leydig cell tumors studied exten sively in our laboratory (4) were found to exhibit some features in common with luteomas and corti cal adenomas. They caused masculinization, progestational effects with deciduoma formation in females, adrenal atrophy and obesity in mice of both sexes, and death from exsanguinating pleuropericardial hemorrhage, predominantly in adult males. The urine of tumor hosts contained a 20to 40-fold increase in two 17-ketosteroids (androstene and an unidentified CigCh steroid). It is most desirable to pursue research with these tu mors in directions indicated above for adrenal tumors. Major directions of research.—It is difficult to state which lines of investigation suggested are major and which are minor. The following three, at least, have great potentialities : 1. Working out the optimal kind of treatment on the basis of secretory capacity and responsive ness of tumors in vitro or in vivo in a given patient. 2. Search for analogs to check excess of tropic and other hormones causing or maintaining neo plasms. In this endeavor, dependent or autono mous tropic tumors can be used for screening; e.g., excessive quantities of TSH play an important role in the genesis of thyroid tumors. Transplantable thyrotropic tumors may be useful tools in search for substances which inhibit thyrotropes. Both fully dependent and autonomous but respon sive tumors can be used for this purpose. Mere re tardation of tumor size, i.e., mass of thyrotropes, will indicate the inhibitory capacity of the sub stance tested. Specificity can be checked with a different tropic tumor. Thyroid weights of the ani mals will reflect upon the quantity of hormone se creted by thyrotropes. Similar assays can be de signed for the mammotropes, aiming at control of mammary tumors. 3. Attempts at prophylaxis of tumors caused by Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research. FuRTH—Hormonal Factors and Tumor Growth endocrines by study of the hormonal status preced ing the onset of tumors, and correction of the "signal" derangement. Thus, there is a wealth of unexplored possibili ties in the domain of endocrine neoplasia in ani mals and of promise to yield information of theo retical and practical value. 8. 9. 10. REFERENCES' 1. BAHN,R. C.; WILSON,H.; ANDERSON,E.; and FURTH,J. Physiological Effects of Prolonged Endogenous Stimula tion of the Adrenal Cortex of the Female Mouse. Proc. 20th Internat. Physiol. Congress, 1956. 2. BATES,R. W.; CLIFTON,K. H.; and ANDERSON,E. Prolactin and Thyrotrophin Content of Functional Transplantable Pituitary Tumors. Proc. Soc. Exper. Biol. & Med., 93:525-27, 1956. 3. BÃœNGELER, W. Geschwülsteund regulierte abhängige Wachstumsstörungen (Hyperplasien) im Rahmen der Cellular- und Relations-pathologie. Ztschr. Krebsforsch., 68:72-102, 1951. 4. CLIFTON,K. H.; BLOCH,E.; UPTON,A. C.; and FCRTH,J. Transplantable Leydig-Cell Tumors in Mice. A.M.A. Arch. Path., 62:354-«8,1956. 5. CLIFTON,K. H., and FURTH,J. Hormonal Influences on Growth and Somatotropic Actions of Autonomous Mammotropes. Proc. Soc. Exper. Biol. & Med., 94:809-14, 1957. 6. COHEN,A. I.; BLOCH,E.; and CELOZZI,E. The in Vitro Response of Functional Experimental Adrenal Tumors to Corticotropin (ACTH). Proc. Soc. Exper. Biol. & Med. (in press). 7. COHEN,A. I.; FURTH,J.; and BUFFETT,R. F. 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Discussion of Problems Related to Hormonal Factors in Initiating and Maintaining Tumor Growth Jacob Furth Cancer Res 1957;17:454-463. Updated version E-mail alerts Reprints and Subscriptions Permissions Access the most recent version of this article at: http://cancerres.aacrjournals.org/content/17/5/454.citation Sign up to receive free email-alerts related to this article or journal. To order reprints of this article or to subscribe to the journal, contact the AACR Publications Department at [email protected]. To request permission to re-use all or part of this article, contact the AACR Publications Department at [email protected]. Downloaded from cancerres.aacrjournals.org on June 18, 2017. © 1957 American Association for Cancer Research.