Dermatofibrosarcoma protuberans arising in the lower labial mucosa: a case report and literature review.

Dermatofibrosarcoma protuberans (DFSP) is a low-grade, malignant, spindle cell tumour with an infiltrative growth pattern and a high local recurrence rate. Cases of oral DFSP are rare. This report describes a case of DFSP occurring in the labial mucosa. A 21-year-old Japanese man was referred with a recurrent mass on the labial mucosa. Oral examination revealed an indurated tumour of 10 mm, extending from the lower labial mucosa to the labial commissure. The lesion was resected with a surgical margin of >10 mm from the induration, under general anaesthesia. The full-thickness labial mucosa to the cheek, with overlying skin and labial commissure, was resected. Pathologically, spindle-shaped cells with pale eosinophilic cytoplasm were observed. Most of the tumour cells exhibited mild to moderate nuclear atypia and were positive for α-smooth muscle actin and CD34 on immunohistochemistry. Based on these findings, a pathological diagnosis of DFSP was made. The postoperative course was uneventful, and no recurrence was observed for over a year. Oral DFSP is extremely rare and challenging to diagnose, and DFSP of the labial mucosa, as reported here, is exceptionally rare. Resection of this locally invasive tumour with a clear margin is important for a good prognosis.