Prostate Cancer, Support Groups  and Prostate Cancer Treatment

High Prevalence of Screening-detected Prostate Cancer among

Afro-Caribbeans: The Tobago Prostate Cancer Survey1

Departments of Epidemiology [C. H. B., A. L. P., L. H. K.], Medicine

[A. M. B., D. L. T.], Urology [B. R. K., C. A. V.], and Pathology [R. D.,

M. J. B.], University of Pittsburgh, Pittsburgh, Pennsylvania 15261;

Department of Medicine, Tobago Regional Hospital, Scarborough, Tobago,

Trinidad & Tobago [A. L. P.]; and University of Pittsburgh Cancer Institute,

Pittsburgh, Pennsylvania 15260 [R. D., A. M. B., M. J. B., D. L. T., L. H. K.]

Prostate cancer is a very serious personal and public health

problem affecting African Americans more frequently than

Caucasians. On the basis of 1990–1997 data from the U.S.

SEER4 of the National Cancer Institute (1), age-adjusted incidence

of prostate cancer is 225 of 100,000 among African

Americans compared with 149 of 100,000 among white non-

726 Vol. 11, 726–729, August 2002 Cancer Epidemiology, Biomarkers & Prevention

75–79 years, in Caucasians, compared with 14 of 100,000, ages

40–44 years, to 10,945 of 100,000, ages 75–79 years, in

African Americans (13).

We hypothesize that risk for prostate cancer is high among

populations of African descent living in diverse environments.

If so, this would lead us to hypothesize that populations of

African descent share genetic and/or lifestyle factors that increase

risk for prostate cancer.

On the island of Tobago, Trinidad & Tobago, we are

conducting a population-based, longitudinal study of prostate

cancer in the male population ages 40–79 years. In this report,

we present data from the initial cross-sectional screening using

serum PSA and DRE.

Recruitment. The recruitment goal was 4000 men, 80% of the

male population of Tobago, ages 40–79 years. Currently,

Informed Consent. Consent was obtained using forms and

procedures approved by the Institutional Review Boards of

University of Pittsburgh Institutional Review Board and the

Tobago Ministry of Health.

Data Collection. Data were collected by locally resident study

staff at the study office located at the Tobago Regional Hospital.

Data collected included ethnicity, education, occupation,

smoking, medical history, personal and family cancer history,

vasectomy, prostate symptoms, health screening history, alcohol

intake, detailed occupational history, and height, weight,

waist, and hip measurements.

Biological Sample Collection. A 15-ml plain vacutainer of

peripheral blood was drawn from fasting subjects. Aliquots of

DRE. A systematic DRE was performed by a physician trained

according to the study protocol. This exam was scheduled after

the blood draw to avoid an artifactual increase in serum PSA

that may follow digital manipulation of the gland.

PSA Measurement. Serum PSA levels were measured at the

University of Pittsburgh Central Pathology Laboratory using

the automated Microparticle Enzyme Immunoassay, Abbot Ax-

SYM PSA assay (Abbott Laboratories, Abbott Park, IL).

Criteria for Referral for Prostate Biopsy. Subjects were

referred to the Tobago Regional Hospital for biopsy if the DRE

was abnormal (except for simple enlargement without palpably

Prostate Biopsy. Prostate biopsies were performed by urologists

or by surgeons trained by urologists from the University of

Pittsburgh Medical Center. Trans-rectal ultrasound guided biopsy

was performed using an 18 gauge, 21-cm spring-loaded

biopsy needle (Boston Scientific, Natick, MA). Sextant biopsies

were obtained according to a standard protocol.

Prostate Pathology. The formalin preserved specimens were

stored at room temperature and shipped to the University of

Pittsburgh for histopathological examination. The specimens

were examined for presence or absence of high-grade prostatic

intraepithelial neoplasia, presence or absence of cancer, Gleason

score of cancer, location of cancer, and perineural invasion.

Data Analysis. Age-specific prevalence rates (per 100

screened men) were calculated. Age-adjusted rates/100 and

SE/100 were calculated by direct standardization (15) based on

the age distribution (50–79 years) of the 1970 United States

standard million population (1). Positive predictive value of the

screening tests was calculated as number of men diagnosed

with prostate cancer divided by the number of men with abnormal

DRE and/or elevated PSA who underwent biopsy. All

statistical calculations were performed using SPSS 10.0 for

Windows (SPSS Inc., Chicago, IL).

PSA and/or DRE screening was completed for 2492 men, ages

40–79 years, 49% of the total male population in this age

group. Eight men who reported prior diagnosis of prostate

cancer are excluded from these analyses. Among the 2484 men

remaining, mean age was 55.9 years, SD was 10.6, and median

was 54 years. Ninety-two percent of men reported three or four

grandparents of African descent, whereas 5% reported one or

two of African descent. Twenty-four percent had completed

secondary school or higher education. Forty-two percent reported

ever smoking, whereas 14% were current smokers.

The serum PSA range was 0.1–18,330 ng/ml. Mean serum

PSA was 14.8 ng/ml and SD was 376. After excluding 4

727 Cancer Epidemiology, Biomarkers & Prevention

relatives included 78 fathers, 65 brothers, 3 half-brothers, 8

uncles, and 2 grandfathers. Thirteen (10.6%) of 123 men reporting

family history of prostate cancer were diagnosed with

prostate cancer, compared with 246 (10.4%) men diagnosed

with prostate cancer among 2361 men not reporting family

history of prostate cancer.

Eight percent of men reported that a physician had told

them they had benign prostatic hypertrophy. Waking to urinate

more than once/night was reported by 51% of men (62% of men

ages 50–79 years). The rate rose steadily from 33% among men

ages 40–49 years to 86% among men ages 70–79 years. Within

each age group, the rate was similar in cases and noncases.

The screening detected prevalence of prostate cancer in this

Afro-Caribbean population, ages 50–79 years, was about three

to four times higher than rates reported from screening studies

of predominantly Caucasian populations (16–18). These

United States studies, which reported results by age group, were

conducted between 1989 and 1992 when PSA screening was

just beginning to be widely used in the United States. After

direct age adjustment to the standard 1970 United States population,

ages 50–79 years (SEER), screening-detected prevalence

in Tobago men, ages 50–79, was 15.1 of 100, SE 0.9,

compared with 3.8 of 100, SE 0.2, in a population of 6501

United States men (92% Caucasian, 3% African American, and

5% other), ages 50–79 years, reported by Richie et al. (18).

Comparison of the age-specific screening-detected prevalence

rates of prostate cancer in these two populations are shown in

Fig. 1.

Factors that may influence the comparison of the screening

results from these two populations include the biopsy protocol,

the proportion of men with abnormal PSA/DRE who underwent

biopsy, prior level of screening in the populations, and recruitment

methods. In the study by Richie et al. (18), quadrant

ultrasound guided needle biopsies were performed, whereas

this study required sextant biopsies, which were likely to have

resulted in some increase in the probability of detecting cancer

if cancer was present (19). The biopsy rate among men with

abnormal screening results was 90% in the Tobago study,

compared with 69% in the study by Richie et al. (18). This

higher biopsy rate increased the opportunity to ascertain cases.

Thus, procedural differences may account for some of the

increased prevalence rate among the Tobago men.

The United States population in the previously mentioned

study (18) was screened in 1991–1992, a period during which

the incidence of prostate cancer was rising sharply (1), reflecting

increasing use of PSA testing. Thus, some prostate cancer

cases may have been removed from this United States population

by prior screening. However, 19% of the Tobago men, ages

50–79 years, reported a prior PSA test, suggesting that some

level of screening had also been available in this Tobago

population.

Both the United States (18) and the Tobago populations

were self-referred. The Tobago population was recruited primarily

by word of mouth. The United States population was

recruited by advertisement. Among the United States population,

53% reported symptoms of prostatism. Sixty-two percent

of Tobago men, ages 50–79 years, reported waking to urinate

two or more times/night. If self-referral bias were to have a

strong effect, one would have expected higher prostate cancer

rates among men recruited earlier in the study compared with

later. As shown in Fig. 2, this was somewhat true, particularly

in the oldest age group among whom symptoms were more

likely to be related to prostate cancer. Compared with the

age-standardized rate of screening-detected prostate cancer

(15.1%) among men ages 50–79 years in the total screened

group, the rate based on the men recruited only in 2000–2001

was somewhat lower, 13.4%. Even after deflating the conservative

13.4% rate by the ratio of the biopsy rates in the two

populations, the even more conservative estimate of the agestandardized

rate of screening-detected prostate cancer of

10.3% is still almost 3-fold higher than in the United States

population, Richie et al. (18).

Similar age-specific prevalence rates from screening of

other populations of African descent have not been published.

Fig. 1. Screening detected prevalence of prostate cancer among 6501 predominantly

Caucasian United States men (18) and 2484 Afro-Tobagonian men.

Table 1 Screening and biopsy results in Tobago men by age group

Age

group (yr)

Screened

Abnormal DRE

and/or PSA n

(% of screened)

Biopsied n (%

of abnormal)

Prostate cancer n

(% of biopsied)

Prostate cancer prevalence

(per 100 screened population)

40–49 843 87 (10) 77 (89) 9 (12) 9/843 (1)

50–59 729 201 (28) 188 (94) 50 (27) 50/729 (7)

60–69 584 262 (45) 240 (92) 107 (45) 107/584 (18)

70–79 328 209 (64) 176 (84) 93 (53) 93/328 (28)

Total age 2484 759 (31) 681 (90) 259 (38) 259/2484 (10)

40–79

Total age 1641 672 (41) 604 (90) 250 (41) 250/1641 (15)

50–79

728 High Prostate Cancer Prevalence in Afro-Caribbeans

Smith et al. (20) reported prostate cancer prevalence of 5.1%

among 804 African-American men screened between 1991 and

1995 using serum PSA and DRE. Application of the Tobago

prostate cancer rates to the reported age distribution in this

African-American population yielded an expected rate of

12.4%, compared with the observed prevalence of 5.1%, suggesting

that the Tobago rates are approximately twice those

observed in the African-American population.

One of the known risk factors for prostate cancer is ethnicity,

i.e., African descent, although we do not know how this

risk is mediated. One hypothesis is that genetic factors contribute

to the high risk for prostate cancer among populations of

African origin. If the Caucasian admixture rate in the Tobago

population is indeed low, then this population may carry a

higher burden of high-risk genes of African descent than the

more admixed populations in the United States.

In conclusion, compared with Caucasian and other populations,

the higher incidence of prostate cancer observed in

populations of African descent, African Americans (1) and

Jamaicans (10), and the very high screening-detected prevalence

of prostate cancer observed in this study among Tobagonians

support the hypothesis that these populations share ancestral

genetic factors that increase susceptibility to prostate

cancer. However, the variability in risk across these populations

of African descent suggests an important influence of unknown

environmental/lifestyle factors acting on prostate cancer risk in

these susceptible populations.

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Fig. 2. Screening-detected prostate cancer prevalence rates by year of recruitment,

Tobago.

729 Cancer Epidemiology, Biomarkers & Prevention