ESR1 and breast adenocarcinoma: On the contrary, metastatic breast adenocarcinoma is often positive for ER and PR.[13] There have been reports that mammaglobin yields better staining in PCAC than in breast adenocarcinoma, and that these 2 tumors can be distinguished based on molecular studies.[14,15] In the reported cases, the probability of metastasis from a primary breast lesion was low as all the patients were men and the tumors were negative for ER and PR.