Relationship of Vasectomy and Prostate Cancer: The Continuing Controversy
Martha K. Terris, M.D.
Assistant Professor of Urology
Chief of Urology, Veterans Affairs Palo Alto Health Care System
Stewart McCallum, M.D.
Assistant Professor of Urology
INTRODUCTION
Prostate cancer is the most common solid tumor in men and vasectomy is the most commonly used male contraceptive method with approximately half a million American men undergoing a vasectomy each year (1,2). Over the years, several studies have suggested an association between vasectomy and prostate cancer while others refute this association (3-8). Evaluation of noncausal factors in men who develop prostate cancer and those who undergo vasectomy have been examined they include sexual activity; androgen levels social differences and the likelihood of prostate cancer detection.9,10 Epidemiological reviews have indicated that patients with prostate cancer appear to be more sexually active, have a greater number of partners, and are more fertile than other men, but not all investigators agree with these findings (9,10). In 1991, The World Health Organization gathered a group of experts to discuss the association between vasectomy and cancer of the prostate and testis (11). This group concluded that " on the basis of existing biological and epidemiological evidence, a causal relationship between vasectomy and the risk of prostatic or testicular cancer was unlikely and no changes in family planning policies concerning vasectomy was justified."
CONFLICTING REPORTS
The controversy gained great publicity in 1993 when Giovannucci et al. published two studies showing strong correlation between vasectomy and prostate cancer. Other studies have subsequently reported contradictory results (3,4). In 1994, Bernal-Delgado et al performed a systematic review of the available literature (12). These authors reviewed fourteen original papers (5 cohort and 9 case-control studies) and concluded that no causal association was present between vasectomy and prostate cancer. Only 3 of the 14 studies determined vasectomy status by methods other than self-report. None of these reported an association and this shows the bias about the collection of information mentioned above. Interestingly, 11 of the 14 studies evaluated in this review reported the existence of an excess risk. In 6 of these studies, the association was statistically significant but Bernal-Delgado et al. demonstrated the existence of numerous methodological problems especially in the studies that showed the greatest increase in risk (12). A review of the literature by DerSimonian et al. also found the evidence to be conflicting with several methodological errors (13).
In 1993, Hayes et al. concluded that young age at vasectomy was an important risk factor in prostate cancer incidence (14). A recent study done by Lesko et al., in June 1999, evaluated the association in a population based case-control study in Massachusetts (15). They concluded that vasectomy does not increase the risk of prostate cancer in men older than 55 years. Similar to the earlier study by they observed an association in men younger than 55 years but encouraged further research to evaluate this result.
POPULATION BIAS
In any evaluation of the relationship between vasectomy and prostate cancer, there is a strong potential for bias in the selection of study participants and in gathering information. The primary issue is that both prostate cancer and history of vasectomy are extremely common in the U.S. male population making enormous numbers of patients necessary to provide reliable statistical information. In addition, since prostatic cancer is usually asymptomatic and slowly progressing, it is not detected in men that do not undergo regular screening examinations. This natural history of the disease generates bias when compounded with the trend that men who have previously seen a urologist to undergo a vasectomy tend to visit urologists more often and hence be more likely to be screened for and diagnosed with prostate cancer. This is supported by the study by Stanford et al., which found that vasectomy and prostate cancer do not have an overall association, but vasectomized men are more likely to be diagnosed with earlier stage, lower grade prostate tumors (7). Additionally white men with relatively high educational levels have been found to be at increased risk for the development of prostatic cancer (14,16). Coincidentally these same groups of men choose vasectomy as a method of contraception more commonly than men with lower socio-economic status (17,18).
CONCLUSION
Clearly, a definitive conclusion has not yet been made. However, multivariate analysis of vasectomy with other potential risk factors such as race, family history, and dietary habits may identify vasectomy as an associated factor but not causally linked to the development of prostate cancer as a primary carcinogen.
When a patient is considering a vasectomy as a potential contraceptive choice, the unsure implication between the procedure and prostate cancer risk should be a routine part of informed consent.
REFERENCES:
1. Greenlee RT, Murray T, Bolden S, Wingo PA. Cancer statistics, 2000, CA Cancer J Clin, 50(1):7-33, 2000.
2. Marquette CM, Koonin LM, Antarsh L, Gargiullo PM, Smith JC. Vasectomy in the United States. Am J Public Health, 85(5):644-9, 1995.
3. Giovannucci E, Tosteson TD, Speizer FE, Ascherio A, Vessey MP, Colditz GA. A retrospective study of vasectomy and prostate cancer in US men. JAMA, 269(7): 878-82, 1993.
4. Giovannucci E, Ascherio A, Rimm EB, Colditz GA, Stampfer MJ, Willet WC. A prospective cohort study of vasectomy and prostate cancer in US men. JAMA, 269(7): 873-7, 1993.
5. Rosenberg L, Palmer JR, Zauber AG, Warshauer ME, Stolley PD, Shapiro S. Vasectomy and the risk of prostate cancer. Am J Epidemiol, 132(6): 1051-5, 1990.
6. Sidney S, Quesenberry CP Jr, Sadler MC, Guess HA, Lydick EG, Cattolica EV. Vasectomy and the risk of prostate cancer in a cohort of multiphasic health checkup examinees: second report. Cancer Causes Control, 2(2): 113-6, 1991.
7. Stanford JL, Wicklund KG, McKnight B, Daling JR, Brawer MK. Vasectomy and the risk of prostate cancer. Cancer Epidemiol Biomarkers Prev, 8(10): 881-6, 1999.
8. Zhu K, Stanford JL, Daling JR, McKnight B, Stergachis A, Brawer MK, Weiss NS. Vasectomy and prostate cancer: a case-control study in a health maintenance organization. Am J Epidemiol, 144(8): 717-22, 1996.
9. Steele R, Less REM, Kraus AS, et al. Sexual factors in the epidemiology of cancer of the prostate. J Chron Dis.,24(1):29-37,1971.
10. Schuman LM, Mandel J, Blochard C, et al. Epidemiologic study of prostate cancer: preliminary report. Cancer Treat Rep.,61:173, 1977.
11. World Health Organization Special Committee. Vasectomy and cancer. Lancet, 338: 1586, 1991.
12. Bernal-Delgado E, Latour-Perez J, Pradas-Arnal F, Gomez-Lopez L. The association between vasectomy and prostate cancer: a systematic review of the literature. Fertility and Sterility, 70(2): 191-200, 1998.
13. DerSimonian R, Clemens J, Spirtas R, Perlman J. Vasectomy and prostate cancer risk: methodological review of the evidence. J Clin Epidemiol, 46(2): 163-72, 1993.
14. Hayes RB, Pottern LM, Greenberg R, Schoenberg J, Swanson GM, Liff J, Schwartz AG, Brown LM, Hoover RN. Vasectomy and prostate cancer in US blacks and whites. Am J Epidemiol, 137(3): 263-9, 1993.
15. Lesko SM, Louik C, Vezina R, Rosenberg L, Shapiro S. Vasectomy and prostate cancer. 161(6): 1848-52, 1999.
16. John EM, Whittemore AS, Wu AH, Kolonel LN, Hislop TG, Howe GR, West DW, Hankin J, Dreon DM, The CZ, et al. Vasectomy and prostate cancer: results from a multi-ethnic case control study. J Natl Cancer Inst,. 87(9): 662-9, 1995.
17. Petitti DB, Klein R, Kipp H, et al. A survery of personal habits, symptoms of illness, and histories of disease in men with and without vasectomies. Am J Public Health. 72(5): 476-80. 1982.
18. Philliber SG, Philliber WW. Social and psychological perspectives on voluntary sterilization: a review. Stud Fam Plann. 16(1): 1-29, 1985.
