Collision tumors are characterized by the coexistence of two cancers in the same anatomical site and its pathogenesis remains controversial. Although uncommon, the association of basal cell carcinoma and melanocytic nevus is the most common among combinations of skin tumors. Even rarer is the association of two malignant tumors. We report a case of tumor collision representing melanoma and basosquamous cell carcinoma, a combination not previously described in the literature, since there are no reported cases of melanoma with this type of basal cell carcinoma.

Darier's disease is a rare autosomal dominant genodermatosis. It has an estimated prevalence of 1 in 55,000 to 100,000 individuals, regardless of gender. It is characterized by multiple keratotic papules on the seborrheic areas of the trunk, scalp, forehead and flexures, and the clinical picture is worsened by heat, sun exposure, perspiration and mechanical trauma. Histopathology observed loss of epithelial adhesion and abnormal keratinization. About 10% of cases present in the localized form of the disease. We report a case of segmental Darier's Disease Type I and discuss the main characteristics of this condition.