Collision tumors: A diagnostic challenge Maria Clara Bernardini, MD, a Elvira Moscarella, MD, b Stefania Borsari, MD, b Aimilios Lallas, MD, b Caterina Longo, MD, PhD, b Simonetta Piana, MD, c and Giuseppe Argenziano, MD d Rosario, Argentina; and Reggio Emilia and Naples, Italy Key words: basal cell carcinoma; collision tumors; confocal microscopy appearance; dermoscopy appearance; junction nevus; pigmented lesions. CLINICAL PRESENTATION A pigmented lesion was located on the back of a 40-year-old woman with family history of melanoma and multiple nevi. The lesion was small in size, and clinically symmetric (Fig 1). DERMOSCOPIC APPEARANCE Dermoscopy revealed an asymmetric lesion, presenting a regular pigment network on one side. On the other side, a structureless white background area with blue-gray and brown loosely arranged dots ‘‘in focus’’ were detected (Fig 2). Fig 1. Collision tumor, clinical aspect. A, Clinical overview of the back of a 40-year old woman. The black arrow indicates the lesion of concern. B, Close-up view of a small, symmetric, dark- brown macule. From the Department of Digital Dermoscopy, Instituto Gamma, Rosario a ; Dermatology and Skin Cancer Unit, Arcispedale Santa Maria Nuova Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Reggio Emilia b ; Pathology Unit, Arcispedale Santa Maria Nuova IRCCS, Reggio Emilia c ; and Dermatology Unit, Second University of Naples. d Supported in part by the Italian Ministry of Health (RF-2010- 2316524). Conflicts of interest: None declared. Reprint requests: Elvira Moscarella, MD, Dermatology and Skin Cancer Unit, Arcispedale Santa Maria Nuova IRCCS, Viale Risorgimento 80, 42100 Reggio Emilia, Italy. E-mail: elvira.moscarella@gmail.com. J Am Acad Dermatol 2016;75:e215-7. 0190-9622/$36.00 ª 2016 by the American Academy of Dermatology, Inc. http://dx.doi.org/10.1016/j.jaad.2016.03.021 e215