Does radiotherapy around the time of pregnancy for Hodgkin's disease modify the risk of breast cancer?

PURPOSE: To determine whether the risk of secondary breast cancer after radiotherapy (RT) for Hodgkin's disease is greater among women who underwent RT around time of pregnancy. METHODS AND MATERIALS: The records of 382 women treated with RT for Hodgkin's disease were reviewed and divided into those who received RT around the time of pregnancy and those who were not pregnant. Comparisons of the overall incidence, actuarial rates, and latency to breast cancer between the two groups were made. Multivariate Cox regression modeling was performed to determine possible contributing factors. RESULTS: Of the 382 women, 14 developed breast cancer (3.7%). The increase in the overall incidence (16.0% vs. 2.3%, p = 0.0001) and the actuarial rate of breast cancer among the women in the pregnant group (p = 0.011) was statistically significant. The women treated around the time of pregnancy had a 10- and 15-year actuarial rate of breast cancer of 6.7% and 32.6%, respectively. The 10-year and 15-year actuarial rate for the nonpregnant women was 0.4% and 1.7%, respectively. The median latency from RT to the diagnosis of breast cancer was 13.1 and 18.9 years for women in the pregnant and nonpregnant groups, respectively. In the multivariate analysis, pregnancy around the time of RT was the only variable associated with an increased risk of breast cancer. The risk was dependent on the length of time from pregnancy to RT, with women receiving RT during pregnancy and within 1 month of pregnancy having an increased risk of breast cancer compared with nonpregnant women and women irradiated later than 1 month after pregnancy (hazard ratio, 22.49; 95% confidence interval, 5.56-90.88; p <0.001). CONCLUSION: The results of this study indicate that the risk of breast cancer after RT is greater with irradiation around the time of pregnancy. This suggests that pregnancy is a time of increased sensitivity of breast tissue to the carcinogenic effects of radiation. Because of the small sample size and limited follow-up, additional studies are recommended to confirm these findings.