Abstract
Collision tumors are characterized by the coexistence of two neoplasms in the same anatomical site. The association of melanocytic nevi with mesenchymal proliferations is rare. To date, only sixteen cases of unusual combination of blue nevus and smooth muscle proliferation have been reported. Herein, we report a case of combined blue nevus and leiomyoma. A 71 year-old male presented for a skin check with no personal or family history of skin cancer. Physical exam revealed a dark black macule on his left chest, measuring 4 mm in greatest dimension. Histopathologic examination reveals a proliferation of two cell populations composed of intersecting fascicles of smooth muscle with intermixed pigmented dendritic bipolar spindle melanocytes. The melanocytic component is highlighted by Melan-A stain and the smooth muscle is positive for desmin. No prominent cytologic atypia or mitotic figures are present. The Ki-67 proliferation index is less than 5%. The previous case reports and case series of blue nevus combined with smooth muscle proliferation used the terms smooth muscle hyperplasia and smooth muscle hamartoma. However, our case depicts the smooth muscle proliferation as a discrete mass in the dermis. Therefore, the diagnosis of blue nevus with leiomyoma collision tumor was rendered. To our knowlage, Only 1 case of a cutaneous leiomyoma in combination with a blue nevus has been previously reported in the old literature.