HER-2/neu expression in extramammary Paget disease: a clinicopathologic and immunohistochemistry study of 47 cases with and without underlying malignancy.

Extramammary Paget disease (EMPD) is an infrequent skin cancer sometimes representing a secondary event caused by extension of an underlying carcinoma. Her-2/neu overexpression in breast cancer is correlated with a more aggressive behavior, but anti-Her-2/neu therapy improves survival in these patients. We investigated Her-2/neu expression by immunohistochemistry in cases of EMPD with and without underlying malignancy to try to correlate with tumor recurrence, progression and possible targeted therapy. Forty-seven cases were analyzed (6 from the scrotum, 7 perianal region, 1 axilla and 33 vulva). Two cases had invasive EMPD (one from vulva and one from scrotum). The overall Her-2/neu expression was 31.9%. Of the noninvasive EMPD of the vulva (32 cases), Her-2/neu was shown in 38%. The case of invasive vulvar EMPD was negative. All six scrotal EMPD lacked Her2/neu expression. Her-2/neu was expressed in two of seven perianal cases (33.3%). The EMPD on the axilla (one case) was negative. Eighteen cases had recurrence, and of these, 44.4% expressed Her-2/neu in the initial lesion. A high proportion of EMPD showed Her-2/neu expression (31.9%), indicating that these patients may benefit from targeted therapy. The proportion of positive cases was higher in lesions that had recurred at last follow up (44.4%), suggesting a more aggressive behavior.