Residual skin cancer after preoperative biopsy: Evaluation by Mohs micrographic surgery

Background. Some patients are referred for Mohs surgery with no or minimal clinical evidence of skin cancer at the biopsy site. Objective. To determine the incidence of residual skin cancer at biopsy sites during Mohs micrographic surgery. Methods. We evaluated all patients that underwent Mohs surgery for basal cell and squamous cell carcinomata in one year. The study was carried out prospectively. Debulking was done using a no. 15 blade at the clinical borders of the tumor or biopsy site. All specimens were sectioned at the middle and out to the periphery at 20-μm intervals. Results. Seven hundred and forty-one patients underwent operations. In 390 patients, a biopsy was performed prior to surgery. A total of 351 patients were biopsied as prestaged (chemocheck) during surgery. Ninety-nine (25%) of the preoperatively biopsied patients showed no residual tumor in the debulking specimen or the first layer. Of these 99 patients, 84 had basal cell carcinoma and 15 had superficial or in situ squamous carcinoma. Conclusions. In this study, preoperative biopsy for diagnosis of skin cancer of the face was curative in 25% of patients, despite pathologic diagnosis of incompletely excised tumor. However, as the majority of preoperatively biopsied patients showed residual tumor, Mohs micrographic surgery is indicated in all patients with incomplete removal of skin cancer of the head and neck.