Paired distribution of molecular subtypes in bilateral breast carcinomas

The last decade has revealed fundamental new insight into the existence of intrinsic molecular subclasses of breast carcinomas. By using immunostaining on archival tissue, we classified tumor pairs from 50 patients with bilateral disease into molecular subgroups (luminal, triple-negative basal-like, and triple-negative unclassified). Synchronous tumors showed a slightly higher rate of concordant pairs than metachronous tumors, and luminal tumors were highly concordant regardless of being synchronous or metachronous (P = 0.001 and P = 0.002, respectively). Metachronous cases had a higher degree of discordance if the time interval was longer than 10 years; this was most pronounced for triple-negative tumors. The relationship found between subtypes of bilateral tumors provides additional evidence for the role of host-related factors in determining the molecular type of breast cancer.