[464] Immunohistochemical Techniques To Differentiate Primary Versus Metastatic Mucinous Carcinoma in the Skin

G Levy, A Finkelstein, J McNiff. Yale New Haven Hospital, New Haven, CT

Background: Mucinous carcinoma is a rare entity that can occur in the skin as a primary cutaneous malignancy or as a metastasis, typically from breast or colon.Metastatic and primary cutaneous mucinous carcinomas are morphologically identical.There are reports that staining with antibodies to p63, D240, CK 5/6, and CD15 is helpful in distinguishing primary and metastatic adenocarcinomas in the skin.Few studies, however, have evaluated staining patterns specifically of mucinous carcinomas in the skin.We applied this immunohistochemical panel to primary mucinous carcinomas of the skin, breast and colon, and metastatic mucinous carcinomas to the skin, in an attempt to identify patterns of staining to differentiate between these entities.
Design: Five cases of primary mucinous carcinoma of the skin, breast, and colon were identified in the files of the Departments of Surgical Pathology and Dermatology. Additionally, two cases of metastatic mucinous breast carcinoma to the skin were also identified. These cases were stained with antibodies to p63, CD15, CK5/6, D2-40, CK7, and CK20. The staining pattern of primary cutaneous mucinous carcinoma was compared to staining of mucinous carcinoma metastatic to skin, and primary mucinous carcinoma of breast and colon.
Results: All cases of primary mucinous carcinoma of skin were positive for CK7. Only 40% labeled with antibodies to p63, and all were negative for CD15, D2-40, CK20, and calponin. The breast mucinous carcinomas metastatic to the skin were negative for all markers except CK7. The primary breast carcinomas were all positive for CK7, and negative for calponin, CK20, D240, CK5/6, and CD15. Staining for p63 was identified in 60% of cases of breast mucinous carcinoma. The primary mucinous colonic carcinomas were negative for all markers except CK20.
Conclusions: Unlike other primary adenocarcinomas of the skin, which can often be differentiated from metastases by positive staining for CK 5/6, D2-40 and P63, mucinous carcinomas of the skin are typically negative for these markers. In a small subset of cases (20% in this series), positive labeling for CK5/6 in primary mucinous carcinoma of skin may help establish a definitive diagnosis. Contrary to previous published reports, immunohistochemical stains for myoepithelial cells were not helpful in differentiating primary from metastatic lesions in our series. Labeling for CK7 and CK20 is helpful in differentiating colon carcinoma from breast or skin malignancies, but does not differentiate primary skin lesions from breast metastases to skin.
Category: Dermatopathology

Tuesday, March 10, 2009 1:00 PM

Poster Session IV # 65, Tuesday Afternoon