Familial prostatic cancer risk and low testosterone.

We investigated whether familial factors influence 1) the incidence of prostatic cancer and 2) the plasma content of sex steroids. A 4-fold higher relative risk for the development of prostatic cancer was observed for brothers (n = 257) of prostatic cancer cases (n = 150) compared to their brothers-in-law (n = 202) and males in the general population of the state Utah. The intraclass correlation for plasma testosterone content [intraclass correlation coefficient (r1) = 0.51; P less than 0.01] and the apparent free testosterone concentration (r1 = 0.54; P less than 0.01) were highly significant in nonendocrinologically treated cases and their brothers. Further, sons and their fathers had significant intraclass correlations for both plasma dihydrotesterone (r1 = 0.83; P less than 0.01) and the ratio of testosterone to dihydrotestosterone (r1 = 0.46; P less than 0.05). Probands and their brothers, and sons of the patients with the disease had significantly lower plasma testosterone levels than controls of comparable age. This is the first documentation indicating that familial (possibly genetic) factors are potent risk factors for predisposing men to the development of prostatic cancer and in regulating the plasma content of androgens. Our results indicate that plasma androgen levels in families with prostatic cancer are clustered in the lower range of the normal population. They also suggest that plasma androgen content is more similar within each family with the cancer than among the families without cancer.