[Neck skin collision tumor].

The collision or mixed tumor is a malignant neoplasm of the skin related to sun exposure and incidence rates of up to 1.5%. It displays a distinctive clinical behavior in relation to other malignancies of the skin and the histological diagnosis, characterized by the collision between a basal cell carcinoma and squamous cell carcinoma, i.e., two malignancies with distinct histologies and sharp interface between them. The case reported was of a male, 73-year-old patient, with two cervical lesions progressively growing in recent months. The chosen treatment was surgery. Histological examination showed the presence of squamous cell carcinoma adjacent to basal cell carcinoma. These tumors preferentially occur in light-skinned men in the fifth or sixth decades of life. Their most common location is in the head and neck, especially in the central part of the face. The differential diagnosis of basal-squamous carcinoma is defined by distinct histological criteria, since both tumors have similar clinical behavior. Local recurrence rates vary from 12% to 45%, whereas regional ones are of approximately 7.5%. The main prognostic factors are gender, surgical margins, perineural infiltration and lymph node status. The treatment of choice is resection, radiotherapy being indicated as adjuvant or to inoperable lesions. Local recurrence is the main limiting factor in disease-free survival, with poor results.