Harvard Men's Health Watch

Finasteride to prevent prostate cancer: A new chapter

Two respected medical organizations, the American Urological Association (AUA) and the American Society of Clinical Oncology (ASCO), issued a joint clinical practice guideline on the use of medication to prevent prostate cancer. The guidelines are contained in a detailed and thoughtful 15-page scientific document. But two prominent news organizations promptly reported the nuanced AUA/ASCO deliberations under the headlines "Older men urged to consider a drug to prevent prostate cancer" and "Experts promote baldness drug for prostate cancer." Spurred by these headlines, many men are likely to ask their doctors for a prescription. That may be a reasonable thing for you to do — but only after you understand the pros and cons of the medication and the scientific uncertainties about prostate cancer prevention.

Hormones and the prostate

Androgens are male sex hormones. The name comes from the Greek for "man-maker," and it's well chosen. Testosterone is the major androgen, and it does make the man. Testosterone is required for the development of male genitals during fetal life, and it triggers the sexual awakening of adolescence. Throughout adulthood, testosterone is responsible for libido and for the large muscles, strong bones, deep voice, and body hair that characterize the gender.

Testosterone is also responsible for the growth of the prostate, which begins with the normal hormone surge at puberty. But while testosterone acts directly on most tissues, its effect on the prostate is more circuitous. An enzyme called 5-alpha reductase converts testosterone to another androgen, dihydrotestosterone (DHT), and DHT is the hormone that stimulates the prostate. DHT is also the androgen that acts on hair follicles, but in this case, it can halt growth, triggering androgenic alopecia (male pattern baldness) in men who have inherited the right (or in this case, wrong) genes.

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