RESUMEN
A 67-year-old man presented with a perianal lump that had increased in size. On examination he had a 3-cm irregular, mobile, elevated, red, polypoid lump at the edge of the anus at the 8-o'clock position. Biopsy results unexpectedly revealed a spindle cell lesion extending deep into the subcutaneous tissue with occasional mitoses. The lesion was positive for CD34 and negative for epithelial markers, consistent with dermatofibrosarcoma protuberans (DFSP). Magnetic resonance imaging of the pelvis showed the mass extending deep into the ischiorectal space with no involvement of the external or internal anal sphincter. He underwent excision of the lesion with circumferential margins of 1 cm and formation of a skin rotation flap to achieve primary closure. Histology confirmed DFSP. Both the deep and lateral resection margins were involved. He proceeded to have a wider excision of margins, which was free of any remaining tumor. Dermatofibrosarcoma protuberans is a rare lesion. It most commonly occurs on the trunk; the perianal presentation in this case is unique. Surgical excision and preservation of functionality with cosmesis was an issue in this case, as DFSP is a locally aggressive tumor with a high recurrence rate.