Background: Basosquamous carcinoma (BSC) and metatypical basal cell carcinoma (MBCC) are uncommon tumors poorly defined in the literature. Available studies suggest these tumors carry a greater risk of recurrence and metastases than basal cell carcinomas (BCCs) and, in some studies, squamous cell carcinomas. Formal treatment recommendations are not fully established. Objective: To analyze BSC and MBCC separately, evaluate whether they are distinct tumor subtypes, and analyze Mohs micrographic surgery (MMS) efficacy for BSC and MBCC. Methods: Retrospective review of medical records and histologic specimens was conducted for 293 patients with 303 biopsy-proven BSCs or MBCCs treated with MMS between 1996 and 2004. In total, 32 BSCs and 128 MBCCs were identified. Surgical and follow-up data were analyzed. Results: Kaplan-Meier estimates of recurrence-free survival after MMS were 100% at one year for both tumor subtypes and were 100% for BSC and 93.8% for MBCC at 5 years. Initial mean sizes were 1.5 cm for BSC and 1.3 cm for MBCC. Approximately 7% represented recurrent tumors at surgery. Of six patients with recurrences, none had known metastatic disease. Limitations: Limitations include retrospective design, analysis of only head and neck sites, and small sample sizes. Conclusion: BSC and MBCC showed no significant distinguishing characteristics to separate them into two BCC subtypes. Reported recurrence rates for BSC and MBCC are 12-45% with wide local excision; estimated recurrence rates are 4.1% with MMS. Our study showed recurrence-free survival of 95.1% at five years. Hence, MMS is effective in treating these BCC subtypes.
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