Bilateral breast cancer: one disease or two?

Our purpose was to determine whether bilateral breast cancer depends upon genetic predisposition to multiple tumors or, alternatively, represents two independent sporadic events. Biological concordance of hormone receptors and histopathology in bilateral tumors, family history of breast cancer, age at diagnosis, and survival were evaluated in 88 patients. The immunoreactivity of paired tumors from 51 patients to six different immunocytochemical markers was compared. Neither histologic patterns nor immunocytochemical reactions showed concordance between bilateral tumors. Absence of concordance (other than for estrogen receptors) and lack of associations with positive family history and early age of onset support an interpretation of independent tumor origins and does not suggest a major role for genetic determinants in the majority of cases of bilateral breast cancer.