Microcystic Adnexal Carcinoma Versus Infiltrative BCC: The thin compressed cords of infiltrative BCC can have some similarity to MAC, but if the biopsy specimen is of decent size, larger nests of more obvious BCC are almost always present.
(70) See the section on Microcystic Adnexal Carcinoma above for a discussion regarding distinguishing DTE from MAC based on H&E features.
Microcystic adnexal carcinoma: review of 51 Japanese patients.
Microcystic adnexal carcinoma: collaborative series review and update.
Microcystic adnexal carcinoma: an immunohistochemical reappraisal.
Microcystic adnexal carcinoma. A, Horn cysts in the superficial portion of the tumor give way to small strands with ductal differentiation in the deeper aspect of the tumor.
Mucinous Adenocarcinoma.--Mucinous adenocarcinoma has a slow growth in contrast to other adnexal carcinomas, which has been postulated to be due to the pressure exerted by the extracellular mucin.
A potential role for targeted therapy in a subset of metastasizing adnexal carcinomas. Mod Pathol.
Finally, Liang et al (23) investigated the use of podoplanin to differentiate metastases to skin from various organ sites, including the breast, from primary skin adnexal carcinomas
. In their study, (23) the authors examined 11 cases of metastatic breast cancer to the skin, all of which (100%) were completely negative for podoplanin.
Various immunohistochemical markers have been studied to help distinguish desmoplastic trichoepitheliomas (DTE), infiltrating or morpheaform BCCs, and microcystic adnexal carcinomas, including CD23, CD5, CD10, CD34, CK20, CK15, stromelysin-3, BCL2, AR, pleckstrin homology-like domain, family A, member 1 protein (PHLDA1), p75 neurotrophin receptor (p75NTR), fibroblast activation protein (FAP), Ber-EP4, p63, and others (34-48) (Table 2).
(35,39) [CK20.sup.+] Merkel cells are identified as colonizing DTEs but not BCCs and microcystic adnexal carcinomas. (49) However, the Merkel cells identified in DTE may be few, requiring serial sections, and care is needed to avoid misinterpretation of Merkel cells in preexisting vellus follicles.
If metastatic RCC is a consideration, a useful panel of immunohistochemical stains may include renal cell carcinoma marker (specific for RCC, although not completely sensitive), PAX8 (positive in RCC and negative in cutaneous adnexal carcinomas
), and p63 (negative in RCC and positive in most primary cutaneous carcinomas).