Curettage prior to Mohs' micrographic surgery for previously biopsied nonmelanoma skin cancers: what are we curetting? Retrospective, prospective, and comparative study.

BACKGROUND Curettage prior to excision and Mohs' micrographic surgery for nonmelanoma skin cancer is performed based on the assumption that the curette will remove softer, more friable tumor-infiltrated dermis and leave structurally intact normal skin. This assumption, however, has not been objectively examined in the dermatologic surgery literature. OBJECTIVE We performed a study to examine the ability of curettage to selectively remove and delineate nonmelanoma skin cancer prior to Mohs' micrographic surgery. METHODS The study included 150 previously biopsied basal cell and squamous cell carcinomas less than 1.5 cm in size. We conducted (1) a retrospective study of 50 tumors curetted prior to Mohs' surgery by a surgeon who routinely curettes preoperatively; (2) a prospective study in which a surgeon who routinely does not curette preoperatively curetted 50 tumors prior to Mohs' surgery; and (3) a comparative historical group of 50 noncuretted tumors treated with Mohs' surgery by the latter surgeon. All curetted tissue was evaluated histologically. RESULTS Only 50% of the curetted tissue demonstrated the presence of tumor in the curettings, but in 76% of these, the curette left residual tumor at the surgical margins. Of the other 50% in which the curette removed only non-cancer-containing skin, 34% had tumor present at the surgical margin. Overall, the curette removed tumor, leaving no residual tumor at the surgical margins in only 12% of lesions. Comparison with historical noncuretted tumors operated on by the same surgeon showed that curettage did not affect the mean number of stages or the proportion of tumors requiring more than one stage for histologic clearance. CONCLUSION Although curettage may be helpful in debulking friable skin prior to Mohs' micrographic surgery, it does not reliably delineate the extent of a tumor.