A 57-year-old man consulted for a bi-coloured lesion on his back.
Dermoscopy revealed a typical reticular pattern and some brown globules (red circle) in favor of a melanocytic nevus and a lighter brown pigmentation (green circle) without pigment network. Delicate fat fingers were present on this part in favor of a seborrheic keratosis.
The lesion was excised and pathology confirmed the diagnosis of collision tumor which associated a seborrheic keratosis and a melanocytic compound nevus.
A collision tumor is defined as a side-by-side occurence of two tumors (benign or malignant). For example: confluence of a seborrheic keratosis and a basal cell carcinoma, confluence of a melanoma and a BCC, confluence of an angioma and a Clark nevus.
