Download Morphological Aspects of Experimental Actinic

Morphological Aspects of Experimental Actinic and
Arsenic Carcinomas in the Skin of Rats
W. C. Hueper, M.D.
(F'rom the I4"arner Institute /or Therapeutic Research, New Yor/<, N. Y.)
(Received for publication April 25, t942)
Epidermal neoplasms of the human skin vary
greatly in their degree of differentiation and in the
type of special organic morphology which they reproduce. However, this diversity in structure is apparently unrelated to the physical or chemical nature
of the causative carcinogcnic agent. Thus, epidermoid
carcinomas as well as basal cell cancers are elicited
by the action of arsenicals and sonar radiation containing ultraviolet rays. Similar conditions seem to
apply to animals. Putschar and Holtz (8) observed
in the skin of rats exposed to ultraviolet rays not only
these 2 types of blastomas, but also trichoepitheliomas
and spindle cell sarcomatoid carcinomas resembling
those found not infrequently in the skin of mice
subjected to paintings with tar. These observations
show that the skin of rats possesses blastomatous
potentialities which are equal to those of the human
skin in spite of the fact that these tissues differ
normally in their anatomical structure to a considerable degree.
The following study on the morphological aspects
of experimental actinic and arsenic carcinomas in the
skin of rats is presented to emphasize the structural
diversity of the various epithelial tumors produced
by these carcinogenic agents and to add at the same
time several new types of epidermal neoplasms
hitherto not described in irradiated rats.
ACTINIC CARCINOMAS
MATERIAL
The observations to be reported were made in a
series of 20 rats which had been exposed, for a
period of up to to morlths, to the radiation emitted
from the mercury vapor burner of a Hanovia S u p e r s
Alpine Lamp yielding 1,5oo milliwatts per square
centimeter at a distance of 75 cm. Details concerning
the experimental procedures which led in these animals to the development of cancers of the skin, as
well as brief notes regarding the types of tumors
produced, have been given in a previous paper (3).
HISTOLOGICAl. I)ATA
EPIDERMAL HYPERPLASTIC REACTIONS
The primary effect of an exposure to ultraviolet
rays is a thickening of the cornified lamellated layer
and an increase in the number of cellular layers from
the normal I or 2 to 5 or 6. Simultaneously, there
occurs a progressive differentiation of the epidermal
cells in the more superficial layers. They change from
relatively small oval or round cells to large polygonal
cells which, near the cornified lamella, contain eleidin
granules. The cells of the basal layer not infrequently
assume a low cuboidal shape and become arranged
in regular palisade formation. The basal layer is
covered in some areas by one or several layers of somewhat larger round cells.
While these changes represent the most frequent
epidermal reaction, there occur regions in which a
diffuse and irregular proliferation of basal and round
cells takes place without anv appreciable thickening
of the cornified layer and any differentiation into
squamous cells (Fig. i). Some of these atypical
epidermal areas are covered by a layer of debris and
leucocytes. They vary considerably in thickness and
may include areas composed of spindle cells and
squamous cells (Fig. 2).
Following or accompanying these manifestations of
epiderma[ proliferation, differentiation, and disorganization, small well circumscribed buds of round and
oval cells project into the subepidermal vascular cot>
nective tissue. These processes may preserve during
further growth their oval, round, or spindle cell character, or they may develop in their central portions
occasional small epithelial pearls surrounded by a few
flattened squamous calls, or they may undergo progressive differentiation in these parts with the formation
of large masses of polygonal cells and numerous
pearls. The course last mentioned is the most frequent
one, and is often associated with the development of
solid epithelial papillary projections covered by a
thick cornified layer and extending beyond the surface
of the skin.
The increased keratinization of the epidermis results
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Fro. 1.--The epidermis shows proliferation of round cells, which extend in garland formations into the deeper tissue. Mag.
X I55.
Fta. 2.--Beneath a thick cornified layer lies a thickened epidermis, consisting of areas of densely packed spindle epithelial cells
and squamous cell parakeratotic loci. Mag. X *55.
Fro. 3.--Underneath a hyperplastic epidermis large accumulations of sebaceous glands are found. Mag. X 75.
Fic. 4.--Squamous cell carcinoma with cornification. Mag. X 75-
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Hueper
Actinic and Arsenic Carcinomas in Skin
not infrequently in a clogging of the orifices of the
hair follicles which subsequently become distended
thereby and filled with keratinized material and
fragments of degenerated hair. The sebaceous glands
occasionally undergo notable proliferation, and then
form dense adenomatoid clusters (Fig. 3).
These hyperplastic epidermal reactions form the
basis for the subsequent development of various types
of malignant tumors, whose morphological features
are sometimes influenced to an appreciable degree by
the benign or malignant proliferative processes affecting concomitantly the underlying mesenchymatous
tissues.
EPIDERMAL I%~TEoPLASTIC R~ACTtONS
(a) The most common type of actinic carcinoma
in the skin of rats subjected to ultraviolet radiation
is the squamous cell carcinoma with cornification
(Fig. 4). It is identical in all morphological respects
to that seen in the human skin.
(b) The squamous cell carcinoma without cornification is considerably less often encountered under the
experimental conditions stated (Fig. 5)(c) The third type of epidermal neoplasm not infrequently met with in the skin of irradiated rats is
a round cell carcinoma consisting of densely and
irregularly packed, relatively large, not always well
defined, round cells, which grow in large plump
processes and sheets in which a n-targinal gern-tinal
layer is not discernible (Fig. 6).
(d) In son.te instances the cells of such an iml-t-tature neoplasm have an oval or spindle shape, either
in scattered areas or throughout the bulk of the tumor.
These spindle cell carcinomas differ, however, from
the ordinary basal cell carcinoma of the human skin
in that their ceils are larger, they have a more
abundant amount of cytoplasm, and the cellular outlines are sometimes more distinct than those seen
in the spindle cell type of basal cell cancer of human
origin. Morphologically they resemble more closely
the spindle cell carcinomas found in the human
uterine cervix (Fig. 7)- Inasmuch as spindle cell
sarcomas are not rare in the cutaneous tissue of irradiated rats (Fig. 8) and occur in coexistence with
epidermal neoplasms, it is occasionally di~cult to
distinguish between these 2 types of tumors, especially when they collide in the subcutaneous tissue.
The use of silvered preparations for the demonstration
of reticulum and the preparation of sections stained
with phosphotungstic acid-hematoxylin for the demonstration of fibroglia and myoglia is of aid in the differential diagnosis of these tumors (2).
(e) Carcinomas of the basal cell type, consisting
of relatively small, round, oval, or spindle cells with
ill defined outlines and hypochromatic nuclei grow-
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ing either in large, well demarcated islands (Fig. 9)
or composed of hyperchromatic cells forming slender,
garland-like, reticulated structures in a loose, partly
mucinous stroma (cylindromatous type) (Fig. ~o)
occur rarely.
(f) Somewhat more frequent are combinations of
basal cell cancer and squamous cell carcinoma (keratinizing basal cell carcinoma, Fig. I i). The ratio of
the 2 types of structures varies greatly with the individual tumors.
(g) A very rare variety, which was seen only once
in the present series, is represented by an adamantinomatoid type of carcinoma. This is composed of
smaller or larger nests of well outlined cells of
spindle shape surrounded by columnar elements resembling enameloblasts. In some of these alveoli pinkish stained pearls are present, which are embedded
in a reticular, cellular matrix. The intervening stroma
is very loosc and vascular (Fig. i2).
(h) A pseudoglandular type of carcinoma occurs infrequently. It originates from a solid type of epithelial
growth consisting of medium sized, polygonal, or
cuboidal elements which undergo degenerative and
lyric changes in the central portion of the strands
and islands, leaving the peripheral cell layers intact.
This process results in the formation of tubular or
alveolar structures lined by somewhat irregularly arranged epithelial cells (Fig. I3), such as are seen in
pseudoglandular carcinomas of the bladder in dogs
treated with ~-naphthylamine (3)This tumor displays a definite similarity to anglosarcomas occurring in the subcutaneous tissue of
irradiated rats and bordering on or involving the
epidermis. It is important that in the case of anglosarcomas the overlying or adjacent epidermis displays
merely hyperplastic changes without any appreciable
atypical manifestations (Fig. *4)(i) The blastomatogenic effect exerted by ultraviolet rays on both the epidermal and vascular elements of the skin is exemplified, moreover, by the
occurrence of squamous cell carcinomas possessing a
loose, edematous, stroma which contains numerous
dilated and congested blood vessels (Fig. I5). Such
tumors have been termed angio-epitheliomas when occurring in the human bladder or in the skin of mice
painted with tar.
(j) A demonstration of the carcinogenic effect of
ultraviolet rays upon epithelial structures situated
in the subepidermal tissues is presented by the occasional occurrence of carcinomas reproducing in a defective form the structure of the sebaceous glands
(sebaceous carcinomas, Fig. i6). These tumors consist of large, well circumscribed alveoli filled with distinctly outlined epithelial cells possessing a foamy
cytoplasm.
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5:1
1
a *.
FIG. 5.--Squamous cell carcinoma without cornification. Mag. X I55.
Fro. 6.--Round cell carcinoma with densely packed indistinctly outlined round and oval cells. Mag. X 155.
Fro. 7,--Epidermal carcinoma consisting of oval and spindle shaped cells. Mag. X I55.
Fro. 8.--Spindle cell sarcoma surrounding an epidermal cell nest with central necrosis. Mag. X 75.
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Hueper--Actinic and Arsenic Carcinomas in Skin
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Fro. 9.--Small, ill defined round cells with superficial necrosis advancing toward the auricular cartilage. Mag. X I55.
Fro. i0.--Small round and spindle cells growing in reticular formation with a scanty loose stroma. Mag. X I55.
Fro. i i.--Densely packed hyperchromatic round and spindle cells with numerous epithelial pearls. Mag. X I55.
Fro. i2.--Irrcgularly arranged cords of epithelial cells lined by low cuboidal cells which surround a reticulate cellular mass.
The stroma is scanty and very vascular. Mag. X I55.
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Ftc. i3.--Tubular and alveolar cavities lined by irregularly arranged cuboidal cells representing pseudoglandular carcinoma.
Mag. X 155.
FIG. I4.--Ill defined cells of irregular shape and size lining small and large cavities filled with erythrocytes and forming in
part the cellular framework of these structures. Mag. )~ I55.
Fio. I5.--Atypical squamous cell carcinoma with an extraordinary development of vascular stroma. Mag. X 75FIo. 16.--Densely packed long, oval, and spindle epithelial cells with a foamy cytoplasm arranged in relatively well defined
alveoli showing a certain resemblance to sebaceous glandular structures. Mag. X 155.
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Hueper--Actinic and Arsenic Carcinomas in Skin
(k) A relatively rare type of actinic carcinoma
is represented by anaplastic carcinomas. They are
characterized by a kind of dissolution of the epidermis
into highly atypical cells which vary greatly in size,
shape, staining properties, and distinctness of outline.
They invade the subcutaneous connective tissue diffusely in small groups or as solid sheets (Fig. I7).
Their diagnosis sometimes offers great difficulties, as
they have to be distinguished from equally atypical,
polymorphous cell sarcomas occurring in the subcutaneous tissue of irradiated rats (Fig. t8) and in
direct contact with the often hyperplastic and hyperkeratotic epidermis. This usually shows an intact
basal layer.
(t) The relatively thin epidermis of the rat, which
permits a ready penetration of the ultraviolet rays
into the subepidermal connective tissue, is responsible
not only for the frequent occurrence of sarcomas in
these tissues but also for that of carcinosarcomatous
collision tumors. They are usually squamous cell
carcinomas with an atypical, spindle cell sarcomatous
stroma (Fig. I9).
ARSENIC CARCINOMAS
In spite of the fact that the epithelium lining the
clogged and distended hair follicles was usually hyperplastic and hyperkeratotic, there was not a single
instance of trichoepithelioma found in the ultraviolet
light series. This is remarkable, as these tumors are
relatively common in the skin of mice subjected to
applications of tar, which penetrates into the lumen
of the follicles and thus establishes direct contact with
their epithelial lining. It is of significance for this
reason that a tumor showing trichoepitheliomatous
structure was observed in i out of ~o congenitally
hairless rats which had received with their drinking
water increasing amounts of arsenious acid in the
form of Fowler's solution (Fig. 2o). Hairless rats
were employed in this experiment because the absence
of hair impairs the ready excretion of arsenic by the
skin and its appendages and thus favors the retention
of this carcinogenic agent, especially in the epithelial
lining of the cystically distended hair follicles. Hairless rats normally develop papillary warts in their
hyperkeratotic skin, which possibly might possess
an increased tendency toward a malignant degeneration under the stimulus of an exogenous carcinogenic
agent.
The tumor was found in the last rat surviving for
2i monthsl It was located beneath the epidermis in
the subcutaneous tissue and represented a more or less
well defined nodule measuring about ~ cm. in diameter. It was the only tumor observed in this series
as well as in a series of haired and identically treated
control rats which were litter mates of the hairless
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rats. Six of these haired rats survived for more than
23 months without showing any skin lesions.
DISCUSSION
The evidence presented is satisfactory proof that
under proper stimulation (ultraviolet rays, arsenic)
the epidermis of the rat is capable of producing as
great a variety of carcinomas as that seen in the
human skin. The carcinomas obtained in the skin of
rats following an exposure to ultraviolet rays are even
more complex than those occurring in man, as they
are not infrequently associated with hyperplastic or
sarcomatous proliferations of the mesenchymatous
elements of the cutis, complications rare in tumors of
the human skin. The great variety of epithelial
tumors and their frequent combination or coexistence
with mesenchymatous neoplasms observed in these
animals is attributable to some extent to the fact that
the skin of the rat is much thinner and less cornified
than the human skin, so that the ultraviolet rays
can penetrate deeper into the subepidermal tissue and
elicit blastomatous responses both from the appendages
of the skin and from thc mesenchymatous tissues.
However, the occurrence of tumors differing widely
in structure, yet located side by side in the skin of
the exposed animals, indicates that the diversity depends not entirely upon the action of the carcinogenic
agent as determined and modified in its degree and
depth by the thickness of the keratin and cellular
layer and by the density and distribution of pigmentation and hairs. The type of photochemical changes
elicited in the skin seems to play a major role in this
respect. These, in turn, seem to depend upon endogenous factors of metabolic nature and are responsible
for the kind of pathological "internal environment"
produced in the irradiated tissue, thereby providing
a certain steering mechanism in the carcinogenic
process.
The validity of this concept receives some support from the fact that repeated attempts to elicit
carcinomas of the skin in rabbits by prolonged exposure to ultraviolet rays have failed consistently, in
spite of the production of such tumors with the aid
of another actinic agent, roentgen rays. Inasmuch as
the anatomical structure of the skin of the rabbit does
not differ essentially from that of the rat it has been
argued that intrinsic factors related to the herbivorous
metabolism of the rabbit, and particularly to its
lipoidal aspects, are responsible for this resistance of
the skin.
Baumann and his associates ( i ) attempted, therefore, to overcome this metabolic influence by feeding
cholesterol to rabbits during the course of irradiation
treatment. However, their results were negative. The
writer's own experiments, conducted for a similar
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Cancer Research
: i:
fig. 1 7
f i r 18
Fro. 17.--Diffuse and highly anaplastic proliferation of the basal cell layer into the subcpidermal tissue. Mag. X I55,,
Fro. iS.--Polymorphous cell sarcoma underncath a hyperkeratotic and hyperplastic epidermis. Mag. )K I55.
Fro. Ig.--Nests of cornified squamous cell carcinoma imbedded in a polymorphous cellular sarcoma. Mag. )K 75Fw.. 2o.--Dcnsely packed nests of small cuboidal and oval cells surrounding frequently hyaline lamellated loci which contain
occasional abortive hair formations. Mag. X i55.
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Hueper--Actinic and Arsenic Carcinomas in Sl(in
purpose several years ago with 17 white coated and
blue eyed rabbits (crosses between Chinchilla and
N e w Zealand Red rabbits), were equally unsuccessful.
The skin of the back in 8 of these rabbits was shaved
with an electric razor daily and was then exposed for
increasing periods of time to ultraviolet rays. Moreover, the rabbits were given Fowler's solution by
mouth in order to provide an additional specific
carcinogenic stimulus and to enhance at the same time
the photochemical action of the rays by the production of a chemical photosensitivity. A control series
of 9 rabbits:received actinic treatment only. D u r i n g
the experimental period, which lasted up to I2 months,
all rabbits developed a chronic dermatitis with multiple and sometimes deep ulcerations, keratoses, pigmentary shifts, disturbances in the growth of hair,
scaling, chronic congestion, etc. T h e epidermis of the
back and o f the ears showed hyperplastic, hyperkeratotic, and atrophic changes. These alterations were
not infrequently associated with numerous small ulcerations and with a ballooning of the basal cells. T h e
basal cell layer of the skin of the ears often exhibited
a diffuse proliferative budding of these cells, but in
only one instance was there a displacement of discrete
basal cell nests into the deeper tissue. T h e definite
proliferation of the auricular cartilaginous tissue occasionally noted provided additional evidence concerning
the deep penetration of the rays. These cutaneous
changes were most decided in the rabbits of the arsenic
series. Thus, endogenous metabolic factors seem to
control the type and degree of proliferative epithelial
response to ultraviolet rays, and in some species apparently exert a sort of protective action which, however, may not be absolute, as shown by similar observations m a d e in connection with tar carcinogenesis.
Although arsenical epidermal cancer in m a n has
appeared in the form of cancroid, mixed basal and
squamous cell carcinoma, basal cell cancer, and
Bowen's dyskeratosis, the few experimental arsenic
carcinomas produced in mice or rabbits have all been
squamous cell carcinomas (4, 9).
T h e trichoepithelioma found in the skin of a congenitally hairless rat treated with Fowler's solution represents,
therefore, a new morphological type of epidermal
cancerous response to this agent. The frequent failure
experienced in attempts to cause cancer of the skin
in animals (mice, rats, rabbits) by the oral, parenteral,
or cutaneous administration of various arsenicals may
be related to the fact that arsenic cancer has a relatively long latent period, usually surpassing that of the
559
average life span of the species used in such experiments. This contention is supported by the observation that animals with a much longer life span (horses,
sheep, deer) have developed an environmental type of
arsenic carcinoma of the skin or of the nasal mucous
membranes (5-7)CONCLUSIONS
The evidence presented is proof that the epidermis
of the rat is capable of producing under proper stimulation (ultraviolet rays, arsenic) as great a variety of
carcinomas as that seen in the h u m a n skin.
T h e carcinomas obtained in the skin of the rat
following an exposure to ultraviolet rays are even more
complex than those occurring in man, as they are not
infrequently associated with hyperplastic or sarcomatous proliferations of the mesenchymatous elements of
the cutis.
The average life span of the rat is apparently shorter
in general than the latent period of experimental
arsenic carcinoma.
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Research.
Morphological Aspects of Experimental Actinic and Arsenic
Carcinomas in the Skin of Rats
W. C. Hueper
Cancer Res 1942;2:551-559.
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