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IJE vol.34 no.1 © International Epidemiological Association 2004; all rights reserved.
Advance Access publication 16 September 2004
International Journal of Epidemiology 2005;34:193–197
doi:10.1093/ije/dyh332
OTHER ORIGINAL PAPERS
Sexual behaviour, history of sexually
transmitted diseases, and the risk of prostate
cancer: a case–control study in Cuba
Leticia Fernández,1 Yaima Galán,1* Rosa Jiménez,1 Ángela Gutiérrez,1 Marta Guerra,1 Celia Pereda,1 Celia
Alonso,1 Elio Riboli,2 Antonio Agudo3 and Carlos González3
Accepted
9 August 2004
Background The relationship between the risk of prostate cancer and sexual activity and
history of sexually transmitted diseases was investigated in a case–control study
conducted in Cuba aimed at assessing the effect of lifestyle and environmental
factors, as well as hormonal and genetic factors, on the occurrence of this disease.
Methods
During the period 1998–2000, all men up to 84 yr old with newly diagnosed,
cytologically and/or histologically confirmed prostatic cancer who were resident
in Havana City were identified in nine major hospitals in the area. Controls were
resident in the same city, frequency-matched by age (± 5 years) and hospital. The
study included 273 cases and 254 controls. Information was obtained through an
interview.
Results
The risk of prostate cancer was increased among men with a history of venereal
disease (odds ratio = 1.7, 95% CI = 1.1–2.5). A higher frequency of cases reported
having had sex with prostitutes, although the estimate of relative risk did not reach
statistical significance. Similarly, a nonsignificant positive association was found with
the number of female sexual partners. A significant increased risk was observed
in subjects who reported having sexual intercourse more than 7 times per week
compared with those who reported a weekly frequency of 3 times or fewer (odds
ratio = 2.1, 95% CI = 1.2–3.7). Moreover, a significant trend was demonstrated.
Conclusions The study supports the hypothesis that an infectious factor related to sexual
behaviour could be involved in the occurrence of prostate cancer. A role for
hormonal factors related to sexual activity cannot be ruled out.
Key words
Case–control studies, prostate cancer, sexual behaviour, sexually transmitted
diseases.
1 Co-ordinator group of the project in Cuba, National Institute of Oncology,
Havana, Cuba.
2 International Agency on Research on Cancer (IARC), Lyon, France.
3 Catalan Institute of Oncology, Barcelona, Spain.
Collaborative group: Ivette Portilla, Julia Cruz, Santiago Quintero, Vicente
Osorio, Maria Victoria López, Raúl Espinosa, Rosa Jorge, Olga Piera,
Wilfredo Domínguez, Mario Coll Ruíz, Nora Cañizares, Sergio Ferrán, Lic.
Alexis Janero, Teresa Martí, Celestino Labori, Rosaura Rego, Walfrido
Beiries, Blanca Blanco, Francisco Alonso, and Enrique Abraham.
Participating institutions: Instituto Nacional de Oncología y Radiobiología,
Hospital Clínico Quirúrgico Hnos Ameijeiras, Hospital Clínico Quirúrgico
Enrique Cabrera, General Hospital Calixto García, Hospital Clínico
Quirúrgico Freyre Andrade, General Hospital Joaquín Albarrán, Hospital
Clínico Quirúrgico Salvador Allende, Hospital Clínico Quirúrgico de 10 de
Octubre, and Hospital Clínico Quirúrgico Manuel Fajardo.
* Correspondence: Instituto Nacional de Oncología y Radiobiología,
Vicedirección de Investigaciones, Registro Nacional de Cáncer, 29 y F, Vedado,
CP 10 400, Ciudad de La Habana, Cuba. E-mail: [email protected]
Cancer of the prostate is the second most frequently diagnosed
nonskin cancer in men1 in Cuba (15% of all new cancer cases)
and the second most common underlying cause of cancer death,
accounting for ~19.4% of all cancer mortality.2 The annual
incidence of prostate cancer in Cuba (age-adjusted by world
standard population) is 31.3 per 100 000 men, within the range
of overall rates from Central America (26.9 per 100 000) and
the Caribbean countries (38.6 per 100 000).3 It is substantially
higher than the very low rates in Eastern Asia (3.4 per 100 000)
and less-developed countries (7.7 per 100 000) but far from the
high incidence in more-developed countries (46.6 per 100 000)
or Northern America (102 per 100 000).3 The occurrence of
prostate cancer in Cuba increased from 20.7 per 100 000 in
1977 to 28.6 per 100 000 in 1999. This increase seems not to
have been influenced by diagnostic practices, since screening or
193
194
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
case-finding using prostate-specific antigen is not done on the
island.
Despite many aetiological studies having been carried out
on prostate cancer, no modifiable risk factors have been clearly
established. All that is known with certainty is that the incidence
increases with age, varies by geographic area, by race or ethnicity,
and is higher among men whose father or brother had the disease.4
Several epidemiological studies have suggested that factors related
to sexual behaviour and sexually transmitted diseases may be
associated with prostate cancer.4 A recent meta-analysis5 has
reported slight increases of risk associated with the number of
sexual partners and history of sexually transmitted infection.
Although the mechanisms are unclear, the search for potential
infectious agents involved in prostate carcinogenesis is an
important focus of research; identification of an infectious cause
would be a major advance in the efforts to prevent prostate cancer.
In this article we report results regarding sexual activity and
history of sexually transmitted diseases from a case–control
study carried out in Cuba, a country where a significant
proportion of the population is of African origin. The aim of
the study was to assess the effect of lifestyle and environmental
factors, as well as hormonal and genetic factors, on the
occurrence of prostate cancer in this population.
Patients and methods
During the period 1998–2000, all men up to 84 years old with
newly diagnosed, cytologically and/or histologically confirmed
prostatic cancer who were resident in Havana City were
identified in nine major hospitals in the area. The city notifies
~22% of all new prostate cancer cases in Cuba, and the
participating hospitals cover 90% of new prostate cancer cases
resident in Havana City according to the National Cancer
Registry. In all cases the tumour was graded and staged according
to the Gleason and Union Internationale Contre le Cancer (UICC)
classifications, respectively.6,7 Controls were selected from
patients admitted to the participating hospitals who were resident
in the same city and who had never been diagnosed with benign
prostatic hyperplasia or cancer. The eligible controls were
identified through the list of admissions from all departments and
underwent clinical examination to rule out the presence of a
palpable tumour in the prostate. The control series was designed
to be of equal size to the case series, frequency-matched by age
(± 5 years) and hospital. Both cases and controls suffering from
dementia, Parkinson’s disease, or any other condition that did not
allow the interview were excluded.
Cases and controls were interviewed at the hospital by
trained interviewers. The interviews lasted 40 min on average
and were based on a structured questionnaire. The data
obtained included information about demographic characteristics, marital status, smoking habits, occupational history,
physical activity, personal and family medical history, skin
colour, first-degree family with prostate cancer, sexual
behaviour, and dietary habits. Additionally, height and weight
were measured and 20 ml of venous blood were collected from
all subjects. In terms of their history of sexually transmitted
diseases, subjects were asked whether they had ever been
diagnosed with venereal disease, their age at the onset and
whether they had received medical treatment. Questions
related to sexual behaviour included the age at which they first
had intercourse, their weekly frequency of sexual intercourse
during adult life, their lifetime number of female sexual
partners, and whether they had ever visited prostitutes.
Ethical approval for the study was obtained and an informed
consent was signed by each subject who agreed to participate in
the study.
Unconditional logistic regression models were used to
compute odds ratios (ORs) and to estimate 95% confidence
intervals (95% CIs).8 Tests for linear trends were carried out
using ordinal or categorical variables as continuous in the
logistic regression. Unless otherwise specified, all logistic models
included as covariates age group, hospital, educational level,
skin colour, and having a relative with prostate cancer.
Results
Of 306 patients with histologically confirmed prostate cancer,
20 could not be interviewed due to their bad health status,
5 had previously been treated, 4 did not return to the hospital
after diagnosis, 3 refused to participate, and 1 patient died
before we were able to contact him. As a result, 273 cases
(89.2% participation) were included in the study. According to
the tumour extension, 168 cases (61.5%) presented with local
disease, 19 (7%) had regional disease, and 39 (14.3%) had
disseminate disease; information on extension was missing for
47 cases (17.2%). From 345 eligible controls, 254 were finally
included (73.6% participation). The main reasons for exclusion
were the bad health status of 51 subjects (14.8%), refusal to
participate by 20 (5.8%), and other reasons, including death,
for the remaining 20 (5.8%). Most controls were hospitalized
for general examination, hypertension, heart failure,
respiratory disorder, cerebrovascular disease, or bone pains.
Table 1 shows certain demographic characteristics of cases
and controls. There were no differences by age, marital status,
and educational level. No statistically significant association was
Table 1 Main characteristics of cases and controls
Cases (273)
Controls (254)
n
(%)
n
(%)
Age group
55 yr
55–64 yr
65–74 yr
75–84 yr
7
46
125
95
(2.6)
(16.8)
(45.8)
(34.8)
9
57
114
74
(3.5)
(22.4)
(44.9)
(29.1)
Educational level
None
Primary school
Technical level
University degree
103
106
49
15
(37.7)
(38.8)
(17.9)
(5.5)
82
91
62
19
(32.3)
(35.8)
(24.4)
(7.5)
Skin coloura
White
Black
Mixed
141
65
64
(52.2)
(24.1)
(23.7)
146
51
55
(57.9)
(20.2)
(21.8)
Marital status
Married
Single
Divorced
Widowed
180
27
31
35
(65.9)
(9.9)
(11.4)
(12.8)
162
38
30
24
(63.8)
(15.0)
(11.8)
(9.4)
Family history of prostate cancer
No
250
Father or brother
19
Other
4
(91.6)
(7.0)
(1.5)
238
13
3
(93.7)
(5.1)
(1.2)
a Excluded: three cases and two controls with skin colour ‘yellow’.
SEXUAL BEHAVIOUR, HISTORY OF STDS, AND PROSTATE CANCER
195
transmitted disease, our results support the hypothesis that a
sexually transmitted agent may be related to the occurrence of
prostate cancer. Our results suggest as well a potential effect on
prostate cancer associated with high sexual activity during adult
life as measured by the frequency of sexual intercourse.
A series of early epidemiological observations suggested that
ethnic and geographic differences found in prostate cancer rates
might be due in part to variations in male sexual behaviour
or sexual activity.9 A review10 stated that there was reasonably
consistent evidence suggesting an increased risk of prostate cancer
associated with a high level of sexual activity and/or a history of
sexually transmitted disease. A more recent review4 summarized
the main conclusions of studies issued during the 1990s. Most
studies supported a positive association with a self-reported history
of sexually transmitted diseases, mainly gonorrhoea and syphilis,
although the associations were seldom statistically significant. Age at
the time of first intercourse was often associated with an increased
risk of prostate cancer, whereas lifetime number of sexual partners
was not found to be associated in most studies. The review noted,
however, that many studies were small and had methodological
limitations. Contrary to these conclusions, a large population-based
case–control study11 reported a significant trend of increasing risk
with increasing number of female sexual partners; there was also a
higher risk for subjects with younger age at first intercourse, but this
association became weaker after controlling for the lifetime number
of sexual partners. Finally, in a recent meta-analysis5 there was a
modest but significant linear increase in the estimated risk of
prostate cancer by number of sexual partners, similar in populationand hospital-based studies. There was a lack of association with age
at first intercourse, age at first marriage, or multiple marriages. From
studies that reported age-specific frequencies of sexual intercourse
it was estimated that there was a significant increase in risk with
increasing frequency of sexual activity. In terms of sexually
observed between skin colour and prostate cancer risk,
although the proportion of subjects with black skin colour was
slightly higher for cases than for controls; the OR (95% CI) for
black as compared with white skin colour was 1.32 (0.83–2.08).
Similarly, a higher proportion of cases than controls had a
family history of prostate cancer, but the difference was not
statistically significant: OR (95% CI) = 1.47 (0.72–2.98).
The risk of prostate cancer (Table 2) increased among men with
a history of venereal disease (OR = 1.7, 95% CI = 1.1–2.5),
mainly when it was diagnosed before 30 years of age. Almost all
subjects with a history of venereal disease (86 out of 87 cases and
53 out of 54 controls) reported that they had received medical
treatment. More than 67% of cases and 59% of controls reported
having had sex with prostitutes, producing an increased risk of
prostate cancer, although the estimate did not reach statistical
significance. Cases tended to report a higher number of female
sexual partners, but this was not a risk factor for prostate cancer.
About 46% of cases and 36% of controls reported having had
sexual intercourse more than 7 times per week during adult life,
with a significant increased risk as compared with those who
reported a weekly frequency of 3 times or fewer (OR = 2.1, 95%
CI = 1.2–3.7); furthermore, this showed a significant trend. When
the frequency of sexual intercourse was introduced into a model
together with history of venereal disease and of visiting
prostitutes, its point estimate and trend remained unchanged
(results not shown), suggesting an independent effect.
Discussion
We observed a positive association of risk of prostate cancer with
a history of prior venereal disease, mainly at young ages, and
an increase of risk among men who had sex with prostitutes.
Although our study does not involve any specific sexually
Table 2 Risk of prostate cancer according to factors related with sexual behaviour
Cases
Controls
n
(%)
n
(%)
Odds ratio
95% CI
P-value
186
87
78
9
(68.1)
(31.9)
(28.6)
(3.3)
200
54
46
8
(78.7)
(21.3)
(18.1)
(3.1)
1
1.7
1.7
1.1
1.1–2.5
1.1–2.6
0.4–3.1
0.06
88
183
(32.5)
(67.5)
103
150
(40.7)
(59.3)
1
1.4
0.9–2.1
62
64
49
98
(22.7)
(23.4)
(17.9)
(35.9)
56
48
60
90
(22.0)
(18.9)
(23.6)
(35.4)
1
1.3
0.7
0.9
0.7–2.2
0.4–1.3
0.6–1.6
0.49
Age at first intercourse
16 yr
17–19 yr
20–22 yr
23 yr
147
96
16
14
(53.8)
(35.2)
(5.9)
(5.1)
157
66
20
11
(61.8)
(26.0)
(7.9)
(4.3)
1
1.7
0.7
1.5
1.1–2.5
0.3–1.5
0.6–3.5
0.30
Frequency of sexual intercourseb
0–3 times/week
4–7 times/week
7 times/week
42
104
126
(15.4)
(38.2)
(46.3)
45
118
91
(17.7)
(46.5)
(35.8)
1
1.1
2.1
0.6–1.8
1.2–3.7
0.003
History of venereal disease
No
Yes
Yes, at age 30 yr
Yes, at age 30 yr
Sex with prostitutesa
No
Yes
Number of female sexual partners
0–5
6–10
11–20
21
Estimates adjusted by hospital, age, educational level, skin colour, and family history of prostate cancer.
a Two cases and one control without information; percentages are calculated over 271 cases and 253 controls.
b One case without information; percentage of cases calculated over 272 subjects.
196
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
transmitted diseases, there were significant positive associations for
any sexually transmitted disease, the point estimates being higher
for population-based than hospital-based studies. This association
was further supported by an increased risk among men who visited
prostitutes.
Some sexually transmitted diseases may have been
asymptomatic and therefore underreported. Gonorrhoea and
syphilis may be sentinels for a sexually transmitted infectious
agent that contributes to the aetiology of prostate cancer; in most
studies, however, the exposure was based on a self-reported
history of infection by the subject. In terms of more direct
evidence of an infectious agent, a positive association has been
reported of prostate cancer with long-term persistence of
antibodies to syphilis in serum,12 whereas no associations have
been found with serological response for herpes simplex,
cytomegalovirus, and Epstein–Barr virus.4 Given its association
with sexual practices as well as its role in anogenital infection and
neoplasia,13 a potential aetiological agent to be considered is the
human papillomavirus (HPV), mainly the oncogenic types HPV-16
and HPV-18. The first attempts aimed to detect HPV DNA in
tumour tissue compared with prostate tissue from men with
benign conditions and gave very inconsistent results.4 Two recent
large population-based studies14,15 have reported no association
between serological evidence of HPV-16 or HPV-18 infections and
the development of prostate cancer. In the study of Rosenblatt
et al.14 the association was absent after taking into account the
extension of the disease at diagnosis or measures of tumour
aggressiveness. Furthermore, they did not find any association of
HPV-16 or HPV-18 prevalence with number of sexual partners or
history of gonorrhoea or syphilis among controls. In the study by
Adomi et al.15 there was a significant risk associated with a high
level of antibodies against a less common oncogenic type, HPV-33,
although the authors could not rule out that it was produced by
chance; the result therefore needs to be replicated. These findings
are consistent with several other case–control studies, but they
differ from those of previous nested case–control studies.16,17
However, these studies collected sera more than 20 years before
the diagnosis; although HPV antibodies may persist for decades, it
seems that the level of antibodies decreases in individuals who
do not have recurrent disease. Thus, it has been postulated that
seropositivity for HPV might be a surrogate for sexual activity.
Several studies have reported an association of prostate
cancer with frequency of sexual activity,5 suggesting a possible
link with sexual hormone level. Nevertheless, mechanisms to
explain this relationship are unclear. Androgens are required for
the growth and functional activity of the prostate; on the other
hand, in some men the frequency of sexual activity seems to
be related to hormonal levels. However, although hormonal
factors may contribute to the potential relationship between
prostate cancer and sexual activity, sexual practices are complex
and may not be directly correlated with hormonal levels.
There are several limitations of our study to be considered. First,
almost 90% of potential cases were included, whereas only about
three-quarters of eligible controls could be interviewed. However,
only ~5% of them actively refused to participate. Although the
possibility of differential characteristics among respondents and
nonrespondents can never be discounted, it is unlikely that this
fact could have seriously biased our results. Potential for selection
bias and differential recall bias must always be kept in mind when
controls are selected among hospital patients. In a previous metaanalysis5 there were no differences in many associations according
to the origin of the controls; in terms of association with sexually
transmitted diseases, the estimates from population-based studies
were actually higher than those from hospital-based studies. As
in many previous case–control studies our assessment of exposure
to a sexually transmitted agent relied on a self-reported history of
venereal disease. When subjects were asked whether they were
treated because of the disease all but two provided an affirmative
answer. Apart from age, ethnicity and familial antecedents of
prostate cancer are established risk factors. In our study all these
factors were controlled for in the analysis.
In conclusion our study supports the hypothesis that an
infectious factor related to sexual behaviour could be involved
in the occurrence of prostate cancer. We found a consistent
association with a previous history of venereal diseases, but
the search for potential agents remains a focus of interest. The role
of hormonal factors related to sexual activity, on their own or
interacting with sexually transmitted diseases, cannot be ruled out.
Acknowledgements
This study has been supported by the Catalan Institute of
Oncology, Barcelona, Spain and the International Agency for
Research on Cancer (IARC), Lyon, France (Collaborative
Research Agreement NTR/98/05). The preparation of this
manuscript was also supported by a Fellowship (ICRETT UICC
Fellowship No. 618) from the International Union against
Cancer, awarded to Yaima Galán.
KEY MESSAGES
•
The incidence of prostate cancer in Cuba increased from 20.7 per 100 000 in 1977 to 28.6 per 100 000 in 1999.
•
This increase seems not to have been influenced by diagnostic practices, since screening using prostate-specific
antigen is not done in cuba.
•
Despite many aetiological studies having been carried out on prostate cancer, no modifiable risk factor has yet
been established.
•
An infectious factor related to sexual behaviour is probably involved in the occurrence of prostate cancer in Cuba.
•
A role for hormonal factors related to sexual activity, on their own or interacting with sexually transmitted
diseases, cannot be ruled out.
SEXUAL BEHAVIOUR, HISTORY OF STDS, AND PROSTATE CANCER
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IJE vol.34 no.1 © International Epidemiological Association 2005; all rights reserved.
Advance Access publication 13 January 2005
International Journal of Epidemiology 2005;34:197–198
doi:10.1093/ije/dyh403
Commentary: Is prostate cancer an
infectious disease?
Pelayo Correa
In this issue, Leticia Fernandez and her fellow epidemiologists
from Cuba, Barcelona, and Lyon report interesting findings of
their case–control study in Havana, Cuba.1 The report adds
relevant information supporting the causal relationship
between chronic inflammation and cancer development. The
list of infections and chronic inflammatory states aetiologically
linked to cancer is increasing and includes major human
burdens such as carcinomas of the cervix, stomach, colon, liver,
and bladder as well as some lymphomas. Although the cancer
risk attributable to infections has been quoted as ~15.6%,2 that
estimate does not take into account the risk enhancement effect
of chronic inflammation in multifactorial causal associations in
common cancers such as those of the breast and colon. It is also
well accepted that chronic inflammation affects the prognosis of
cancer by as yet unclear mechanisms. This knowledge has led to
many ongoing intervention trials of inhibitors of inflammation
Louisiana State University Health Sciences Center, New Orleans, LA 70112,
USA. E-mail: [email protected]
such as the non-steroidal anti-inflammatory drugs and the
cyclooxygenase (Cox-2) inhibitors in dozens of cancer sites,
with convincing beneficial effects on prognosis.
Prostatic cancer is the second most frequent malignant
neoplasia worldwide, accounting for 542 990 new cases and
204 313 deaths in 2000.3 The incidence has been increasing
recently in many countries, but the extent of confounding by the
recent introduction and generalization of the PSA test for screening
is difficult to evaluate. The experience in Cuba, where PSA testing
is not done, clearly shows that the increasing trend is real.
Most epidemiological studies have shown that sexual activity
and prostatic cancer are causally associated. Indicators of sexual
activity vary in their association with prostatic cancer in
different studies, but the trend for a risk increase is clear and
consistent.4–6 The association with venereal diseases is also
significant and consistent. These two sets of aetiological factors
are obviously interrelated: greater sexual activity increases the
chances of infection. It seems clear, however, that androgen
secretion, which increases the sexual drive, has an independent