Collision skin lesions-results of a multicenter study of the International Dermoscopy Society (IDS).

Background: Collision lesions as two independent and unrelated skin tumors often manifest an atypical morphology.

Objective: To determine the combinations of collision skin lesions (CSLs).

Methods: Twenty-one pigmented lesion clinics in nine countries included 77 histopathologically proven CSLs in this retrospective observational study.