Successful treatment of metastatic fibrosarcomatous dermatofibrosarcoma protuberans with imatinib mesylate

Dermatofibrosarcoma protuberans (DFSP) is a fibrohistiocytic tumor characterized by a high risk of local recurrence but a low risk of metastasis. A small subpopulation of DFSP undergoes fibrosarcomatous (FS) change, and approximately 15%-57% of cases of DFSP with FS change metastasizes, leading to a poor prognosis. In this report, a case of metastatic FS-DFSP that was successfully treated with imatinib mesylate in which the IHC staining pattern of recurrent DFSP was quantitatively analyzed in primary and metastatic DFSP areas, is described. Importantly, the recurrent area was composed of two IHC staining patterns (CD34^low PD-L1^high Ki67^high , and CD34^high PD-L1^low Ki67^low pattern), while the metastatic area showed a clonal pattern (CD34^high PD-L1^low Ki67^intermediate ) in the present case. In this report, we described a case of metastatic fibrosarcomatous DFSP successfully treated with imatinib mesylate. This case suggests a subpopulation of DFSP with a favorable metastatic pattern.