Reply to Wilms tumor and breast cancer.

Abstract

We appreciate this opportunity to respond to the question raised by Drs Lehrer and Rosenzweig and by others regarding Wilms tumor and male breast cancer. Males account for under 1% of breast cancers in the United States and the disease is especially rare in younger men.(1) Using data from the 9th (1973-1991), 13th (1992-1999) and 18th (2000-2010) SEER registries, we calculated incidence rates of invasive + in-situ breast cancer for men and women under age 40 of 0.0433 and 13.99 per 100,000 person-years, respectively. This yielded an M:F ratio of 0.0031. Assuming that standardized incidence ratio (SIR) for male survivors of Wilms tumor was the same as we found for females, namely 9.2, we made a rough calculation of the number of male breast cancer cases we might have expected had we included men in our study. This calculation also assumed that the number of person-years of observation among males equaled that among females. The latter assumption was conservative since fewer males than females were enrolled on the National Wilms Tumor Studies, whereas death rates for teenage and young adult males are generally slightly higher. We multiplied the number of female cases observed, namely 29 invasive + 6 in-situ = 35, by the M:F ratio to arrive at an expected number of male breast cancer cases of 0.1. Using Poisson statistics, the probability of observing one or more cases of male breast cancer was also only 0.1. In fact, none were observed. Thus the answer is no to the question whether men as well as women had an increased risk of breast cancer after Wilms tumor and radiation in our study. Had we restricted the calculation above to patients receiving chest radiotherapy, assuming that the 30 fold increase we observed for females also held for males, we would have expected only 0.0031×22 = 0.07 cases. More accurately, however, the study was simply uninformative about male breast cancer. We think it likely that chest irradiation for Wilms tumor increases the risk of subsequent breast cancer in men, just as it does in women. However, a much larger population of Wilms tumor survivors, and/or follow-up through the advanced ages at which male breast cancer is more frequent, would be needed to prove the point.