Abstract Background: Basal cell and squamous cell carcinomas (BCC and SCC) are the most common types of cancer worldwide. Intraoperative assessment of surgical margins by frozen section has been widely used to ensure disease-free margins. The intraoperative ‟en face” freezing technique evaluates all peripheral and deep margins. Objective: To report the results of the ‟en face” freezing technique in relation to tumor recurrence and agreement with paraffin-embedded tissue examination. Methods: Retrospective analysis of patients undergoing surgical excision of BCC and SCC at the A. C. Camargo Cancer Center, Brazil. Results: This study included 542 skin carcinomas, which were excised from 397 patients. A total of 201 male patients (50.6%), and 196 female patients (49.4%) were assessed, whose mean age was 64 years. The tumors were mostly located on the head and neck region (87.8%). BCC corresponded to 79.7% of the cases. The mean follow-up was 38 months. Tumor relapse occurred in 0.86% of the primary tumors and 3.7% of recurrent tumors. The result of the intraoperative ‟en face” frozen section evaluation was in agreement with the final result of the anatomopathological examination (paraffin test) in 98% of the lesions. Study limitations: Not having a minimum follow-up time of 5 years for all patients. Conclusion: The ‟en face” freezing technique shows low tumor relapse, being reliable and safe to guarantee negative surgical margins of the tumor.

Histiocitose de células de Langerhans é uma doença rara de causa desconhecida, caracterizada pela proliferação de células histiocitárias (células de Langerhans). Representa significativa dificuldade diagnóstica por apresentar amplo espectro clínico, variando desde uma lesão solitária até uma enfermidade multissistêmica. Pode ser confirmada por estudo imunoistoquímico. O tratamento depende da extensão do processo, podendo ser necessária quimioterapia sistêmica.

Langerhans cell histiocytosis is a rare disease of unknown cause, characterized by the proliferation of histiocytic cells (Langerhans cells). Its diagnosis is especially difficult due to its wide clinical spectrum, ranging from a single lesion to a multisystemic disorder. Diagnosis may be confirmed by means of an immunohistochemical study. Treatment depends upon the severity of the disease, and systemic chemotherapy may be needed.