Letter: Collision tumor: importance of the new auxiliary tools for diagnosis (an illustrative case report).

Collision tumor is a term used to refer to the association of various types of tumors in time and space. Despite most of them not being clinically relevant, sometimes there is a union between a benign lesion and a malignant one. The clinical diagnosis in these cases is usually extremely difficult, particularly if one of the lesions is pigmented. Dermoscopy and confocal microscopy are noninvasive diagnostic methods that make possible the visualization of morphologic structures not visible to the naked eye, thus making diagnosis of these lesions possible. Here we describe a case in which the corrected diagnosis of a collision between a seborrheic keratosis and a basal cell carcinoma was only possible by means of confocal microscopy.