Mohs micrographic surgery of primary cutaneous mucinous carcinoma using immunohistochemistry for margin control

Background. Primary cutaneous mucinous carcinoma is a rare adnexal malignancy with a high recurrence rate following conventional excision and the potential for aggressive local invasion. Objective. To enhance the microscopic detection of mucinous carcinoma in Mohs micrographic surgical sections by incorporating rapid immunohistochemical staining. Methods. Standard Mohs micrographic surgical technique was used in conjunction with frozen section immunohistochemistry using an antibody to low-molecular-weight cytokeratin. Results. Rapid immunoperoxidase staining using low-molecular-weight cytokeratin detected residual foci of mucinous carcinoma that were difficult to identify on routine frozen sections. Immunostaining was strongly positive in areas with clear evidence of tumor by routine histology, as well as in adjacent areas on a subsequent stage where frozen sections were equivocal or negative. Immunostaining was distinctly negative at the final surgical margin, which was shown by en face permanent sections to be free of tumor. The patient has been free of recurrence for 3 years. Conclusion. Immunoperoxidase-guided Mohs micrographic surgery using low-molecular-weight cytokeratin enhances the sensitivity for detection of mucinous carcinoma, and may help contribute to complete tumor removal.