Large asymmetric pigmented nodule in a 27-year-old female.

A 27-year-old female presented with an asymptomatic nodule on the left thigh. She reported a smaller pigmented lesion since birth, with significant growth in the last 5 years. The patient had no personal or family history of skin cancer. She was otherwise healthy and had no systemic symptoms. She was doing oral contraception and no other medications. Physical examination revealed a smooth nodular domeshaped lesion measuring 1 cm × 2 cm, with central hyperpigmented and peripheral erythematous areas, located on the medium third of the anterior left thigh (Fig. 1). There was no regional lymphadenopathy. Dermoscopically there was a central dark hyperpigmented area surrounded by a rim of thin regular pigment network (Fig. 2). In the central area we observed a predominant globular pattern, an eccentric thickened pigment network and a blue-whitish-veil. Excision was performed. Histological examination revealed a compound (predominantly intradermal) melanocytic nevus with congenital-like growth pattern and a dermatofibroma, with no signs of malignancy (Fig. 3). Nevus cells involved deep dermal appendages and neurovascular structures and they became progressively smaller in deeper portions of the lesion suggesting maturation and benignity. Intermingled with melanocytes, there was a proliferation of spindle fibro-histiocytic cells characteristic of dermatofibroma. Collision tumors result from the combination of two or more benign and/or malignant neoplasms in a single lesion.1 As it is unknown whether the association is a random event or whether there is, in fact, a pathogenic relationship in the development of two distinctive neoplasms together, some authors propose the designation of compound tumor