Beautiful ADH arising from FEA. I think there are a couple of peace symbols hiding in there ☮️:) #breastpath

Welcome back to Breast Consult Case of the Week 10 #BCCW10! This one was tricky, and I apologize for leading you astray by not giving you the whole IHC panel, but this is exactly the kind of situation where serious misdiagnoses will happen. The correct answer is myofibroblastoma (MFB) with epithelioid features. The problem, of course, is that MFB is ER and PR positive and E-cadherin negative. Which means that if you do not suspect the diagnosis and don't include CK, CD34, and desmin at the very least, you will be led down the wrong diagnostic path. Some of the useful morphologic features include the following: 1. Amphophilic cytoplasm that tends to contrast with eosinophilic collagen fibers/ropes 2. Open chromatin, no hyperchromasia 3. Despite the contrast between the cytoplasm and surrounding collagen, the cells appear to have a close relationship with the stroma, without clefting or evidence of desmoplasia 4. Often well-circumscribed radiologically Naturally, none of these features is always present or enough on its own. The key here is to consider the possibility and let IHC resolve the issue. One more thing to remember is that MFB is a great mimicker in its own right, with epithelioid, palisaded, myxoid, pleomorphic, and lipomatous variants. And though they're often well-circumscribed, they can show irregular and infiltrative edges on occasion, eliciting clinical concern. Below are images of our case with ER and Desmin, followed by examples of morphologic variants of MFB. Thank you all and see you next week! @washu_pathology @washupathedu #breastpath #PathX #PathX