Histological evaluation of residual basal cell carcinoma after shave biopsy prior to Mohs micrographic surgery

BACKGROUND: Patients who are referred for Mohs surgery after pre-operative biopsy has been performed show in some cases no clinical or pathological evidence of tumour persistence. We have previously shown that 25% of these patients show no residual skin cancer either basal cell carcinoma or squamous cell carcinoma. The reasons for 'disappearance' of the tumour may be true non-persistence or false non-persistence because of wrong-site Mohs surgery. OBJECTIVE: To determine the incidence of residual basal cell carcinoma after shave biopsy of primary nodular basal cell carcinoma prior to Mohs micrographic surgery. METHODS: A prospective unblinded study was performed on patients undergoing Mohs surgery for primary nodular basal cell carcinoma. The tumour was removed as a shaved excision using a No. 15 blade at the clinical borders like a shave biopsy (Mohs shave). The bases of the tumors were excised and then sectioned vertically at the middle and cut to the periphery at 10-15 μm intervals till the edge. RESULTS: Fifty-one patients were evaluated. In 40 patients, residual basal cell carcinoma was found at the base of the shave excision site (78.4%). CONCLUSIONS: Pre-operative shave biopsy performed during Mohs surgery for primary nodular basal cell carcinoma is 'curative' in 22% of the patients.