Case Number : Case 3072 - 15 April 2022 Posted By: Dr. Richard Carr

Cutaneous metastasis. Neuroendocrine carcinoma??? 

EMPSGC!

Definitive looks like a cystic lesion that's mucinous - an in situ component in the form of EMPSGC, and an invasive mucinous carcinoma? IHC appears to be p63 or some other myoepithelial marker proving invasion vs in situ.

Apocrine hidrocystoma. Looks benign with nice decapitation secretion. Mucinous secretion is known in apocrine hidrocystomas.

?? Unusual PCMC with papillocystic features. 

This is a small papillary cystic mucinous carcinoma mimicking a benign cystadenoma. Neuroendocrine markers were negative. In a recent review about 33% of primary cutaneous glandular adnexal carcinomas had a residual myoepithelial cell layer that excludes metastatic carcinoma to the skin. i.e. useful when present but not useful when absent and by far the most likely is a primary cutaneous lesion when this well differentiated. It is also useful here because a benign cystadenoma would have preserved myoepithelial layer throughhout (and no mucin pools). I think 45% of the mucinous carcinomas in the paper below had a partly preserved myoepithelial layer. A small well differentiated lesion like this should have minimal risk for developing metastases. I suggested a modest 5 to 10mm re-excision because mucin pools were abutting margins. In the paper below calponin was considered the best single marker compared with p63 and SMA. I've tend to use p63 as my go to marker.

Plaza, Jose A. MD*; Chung, Catherine MD†; Wick, Mark MD‡; Sangueza, Martin MD§; Gru, Alejandro MD¶ The Utility of Myoepithelial Cell Layer Identification in Adnexal Carcinomas, The American Journal of Dermatopathology: March 2022 - Volume 44 - Issue 3 - p 155-162
doi: 10.1097/DAD.0000000000001844