Cutaneous Desmoplastic Leiomyosarcoma Development at Smallpox Vaccination Site.

An 81-year-old man presented to the clinic with a 2.1 cm firm, skin-colored subcutaneous tumor on the left upper arm (Figure 1). The lesion arose at the site of a past smallpox vaccination and had been slowly enlarging for approximately 4 years. The differential diagnosis included sympastic leiomyoma, and a variety of desmoplastic spindle cell lesions such as desmoplastic melanoma, cutaneous spindle cell carcinoma, and desmoplastic leiomyosarcoma. Punch biopsy and immunohistochemical staining revealed positive spindle cells for desmin and caldesmon (Figures 2 and 3). Immunostain for p53 was also strongly and uniformly positive. Owing to poor circumscription on histopathology, symplastic leiomyosarcoma was ruled out. Demoplastic melanoma was also excluded due to positive immunoreaction to muscle markers (desmin and caldesmon) and negative S-100 staining. Additionally, cutaneous spinde cell carcinoma was also ruled out due to negative p63 and cytokeratin staining. Ultimately, clinicopathologic correlation favored a diagnosis of desmoplastic leiomyosarcoma. Staged excisions were performed to eradicate the lesion.