Expression of p40 in Primary Cutaneous Mucinous Carcinoma Versus Primary Mucinous Carcinomas of the Breast and Colon.

BACKGROUND The transcription factor p63 is a homolog of p53, expressed in basal layers of epithelia and myoepithelial cells. Some studies have suggested that p63 may provide utility in differentiating primary versus metastatic mucinous carcinoma of the skin, given its preferential expression in primary adnexal neoplasms. There have been few studies investigating the expression patterns of p40, an isoform of p63, in primary cutaneous mucinous carcinomas. METHODS An immunohistochemical panel including p40, CK7, CK20, estrogen receptor, and progesterone receptor was applied to primary mucinous carcinomas of the skin, breast, and colon. RESULTS Only a small subset (25%) of primary cutaneous mucinous carcinomas displayed focal positive staining with p40, similar to what has been reported in the literature for p63. All primary mucinous carcinomas of skin and breast labeled positively with CK7, estrogen receptor, and progesterone receptor. Primary colon mucinous carcinomas were only positive for CK20. CONCLUSIONS Based on these results, p40 seems to be an insufficient marker for distinguishing primary versus metastatic mucinous carcinoma due to its low rate of positivity in primary cutaneous mucinous carcinomas.