Clinicopathological analysis of distant metastasis in dermatofibrosarcoma protuberans: a report of 14 cases.

Dermatofibrosarcoma protuberans (DFSP) is a rare sarcoma with a low metastatic rate; however, the prognosis worsens once distant metastasis occurs. We aimed to identify clinicopathological risk factors and molecular features associated with distant metastasis. Fourteen metastatic DFSP cases and 29 matched non-metastatic controls were analyzed for clinicopathological parameters, surgical margins, immunohistochemistry, and COL1A1-PDGFB fusion. Univariate and multivariate conditional logistic regression analyses were performed. Among the 14 patients with metastasis, 78.6 % experienced multiple recurrences. Fibrosarcomatous transformation (FS-DFSP) was predominant in both primary (10/14) and metastatic (13/14) lesions. All patients showed a COL1A1-PDGFB fusion, and lung metastases were identified in 100 % of the patients. The metastatic group exhibited more frequent local recurrences, a higher proportion of FS-DFSP, a higher Ki-67 index, and a higher mitotic count than the control group (all p < 0.01). Local recurrence occurring ≥ 2 times was identified as an independent risk factor for metastasis (OR = 21.49, p = 0.03). In addition, FS-DFSP showed a strong trend toward an association with metastasis (OR = 6.21, p = 0.06). Response to imatinib was heterogeneous. Multiple local recurrences and fibrosarcomatous transformation appear to be key drivers of distant metastasis in DFSP. The COL1A1-PDGFB fusion gene remains a stable diagnostic marker, even in cases with loss of CD34 expression. The lung is the predominant site of distant metastasis. Imatinib demonstrates limited efficacy, highlighting the need for close surveillance of high-risk patients.