ABSTRACT
Cutaneous eccrine and apocrine glands have many histologic and immunologic similarities to ducts and acini of the breast. Thus, differentiating a primary cutaneous process from a metastatic breast carcinoma can be nearly impossible. In all, 10-34% of breast carcinomas overexpress HER-2 protein, a membrane-associated protein that functions in cell differentiation, adhesion and motility. As expression of this gene in cutaneous neoplasms has not been well characterized, we sought to determine HER-2 expression in a sample of benign and malignant cutaneous eccrine and apocrine neoplasms and to determine if there is value in using this protein expression in differentiating primary cutaneous from metastatic breast lesions. Totally, 85 primary cutaneous neoplasms and 11 cutaneous metastases from HER-2-positive breast carcinomas were retrieved from archived material at our institute. All cases were evaluated for HER-2 protein expression using the Dako Hercept Test kit. Membranous HER-2 staining was noted in three of the 85 cutaneous adnexal neoplasms: one hidrocystoma and two nodular hidradenomas. Seven of the 11 cutaneous metastases from HER-2-positive breast carcinomas maintained moderate-to-strong HER-2 expression. In conclusion, while 10-34% of breast carcinomas overexpress the HER-2 protein, only 3.5% of cutaneous apocrine and eccrine neoplasms in this study stained with the HER-2 antibody. These HER-2-positive cutaneous neoplasms typically do not pose a diagnostic dilemma in the setting of differentiation from breast metastasis. Additionally, although histologically these breast and cutaneous lesions may have morphologic similarities, the relative lack of HER-2 overexpression suggests that they are different nosologically. Finally, this study suggests that HER-2 protein expression can be a useful tool in differentiating a primary cutaneous appendageal neoplasm from HER-2 expressing metastatic breast carcinoma.
