Extramammary Paget’s disease (EMPD) is a rare intraepithelial malignancy typically occurring in the groin and axillary regions. Given its indolent growth pattern and clinical resemblance to inflammatory skin conditions, diagnosis of EMPD is often delayed. Reported recurrence rates for standard surgical treatments including wide local excision, vulvectomy, and abdominoperineal resection are high, ranging from 22% to 60% in the largest retrospective cohort of patients with EMPD treated with Mohs micrographic surgery (MMS) demonstrating local recurrence rates of 26% overall, 16% for primary disease, 50% for recurrent disease, and a salvage rate for recurrent disease after MMS (overall cure rate) of 100%

The authors hypothesize that the increased recurrence rates for EMPD after MMS, as compared to other types of skin cancer, are due to difficulties in recognizing tumor cells on routine hematoxylin and eosin staining. Indeed, the authors have previously shown a case of EMPD in the axilla with irregular yet contiguous finger-like microscopic extensions that were not seen on H&E but identified on sections stained for cytokeratin-7(CK-7). The use of intra-operative immunohistochemistry for CK-7 during MMS for EMPD is described in case studies and small single-center cross-sectional studies.

MMS + CK-7 is an effective treatment for EMPD, demonstrating improved outcomes com- pared with historical controls.