Bioavailable serum estradiol may alter radiation risk of postmenopausal breast cancer: a nested case-control study

Abstract

Radiation exposure, higher levels of bE₂, testosterone and progesterone, and established reproductive risk factors were positively associated with postmenopausal breast cancer risk. A test for mediation of the effect of radiation via bE₂ level suggested a small (14%) but significant mediation (p = 0.004). The estimated interaction between radiation and bE₂ was large but not significant (interaction = 3.86; p = 0.32). There is accumulating evidence that ionizing radiation not only damages DNA but also alters other organ systems. While caution is needed, some portion of the radiation risk of postmenopausal breast cancer appeared to be mediated through bE₂ levels, which may be evidence for cancer risks due to both direct and indirect effects of radiation.