How would you manage endocrine therapy in a male patient with gBRCA2 with a metachronous contralateral ER+ breast CA that occurred while on adjuvant tamoxifen for a different ER+ breast CA?

This is a tough situation. There is very limited data on the risk of CBC in men with gBRCA2 pathogenic variants and its impact on survival. In general, men with breast cancer suffer a worse prognosis compared to their female counterparts, although a large part of this may be driven by late stage at diagnosis and under-treatment. (Wang et al., PMID 31536134)

The decision on best adjuvant endocrine therapy for CBC would depend on several factors - adherence to prior tamoxifen, time interval from the original diagnosis, and whether there was a significant gap between initial diagnosis and initiating tamoxifen therapy. I would also, in such cases, look at the use of concomitant drugs and CYP2D6 pharmacogenomics that could impact tamoxifen exposu...