Objective: To investigate the clinical pathological features, diagnosis and differential diagnosis of pigmented dermatofibrosarcoma protuberance (PDFSP).
Methods: The clinical history, histopathological features, immunohistochemical characteristics, treatment and prognosis were analyzed in seven cases of PDFSP. Fluorescence in situ hybridization (FISH) was used to detect the expression of COL1A1/PDGFB fusion gene, and related literature was reviewed.
Results: The median age of the seven patients (4 females, 3 males) was 47 years with the tumors involving mostly the trunk (four cases). Histologically, PDFSP showed a cellular lesion composed of spindle cells arranged in short fascicles that form a distinct storiform pattern, and the pigmented bipolar or multipolar dendritic cells were present with tentacle like processes emanating from a nucleus containing zone. One case showed fibrosarcomatous change. The pigment was tinctorially similar to melanin. The spindle cells were positive for CD34 and vimentin, but negative for HMB45, Melan A, S-100, desmin, CD68 or α-SMA. HMB45, Melan A, S-100 and vimentin were expressed in the melanin containing cells in 4, 4, 5 and 7 cases, respectively. The labeling index of Ki-67 was 1%-8%. Among the 4 cases successfully examined by FISH, 3 showed t(17;22)(q21;q13) which suggested COL1A1/PDGFB fusion gene. Three patients were treated by wide local excision and four were treated by simple surgical excision. Two patients developed recurrences during the follow-up period of 12 to 123 months. Of those treated by wide local excision, none developed recurrence. No patient died in the follow-up period.
Conclusions: PDFSP is a rare pigmented variant of DFSP and an intermediate grade malignant tumor. The orgin of the tumor cells is still controversial. Surgical pathologists and dermatopathologists need to be aware of the prototypical histological appearance of PDFSP as there is a risk of misdiagonsing it as either pigmented tumors associated with neurocutaneous syndromes or a highly malignant melanocytic neoplasm.