Dermatofibrosarcoma protuberans: Neoadjuvant therapy with imatinib mesylate and use of plasma PDGF-B levels to monitor clinical response

Abstract

9049 Background: Dermatofibrosarcoma protuberance (DFSP) is a rare soft tissue sarcoma; most cases show t(17:22) resulting in a COL1A1-PDGF-B fusion protein. It is believed that DFSP arises through dysregulated PDGF-B expression and autocrine PDGF-R stimulation. Imatinib mesylate, a known inhibitor of the PDGF receptor tyrosine kinase, has produced responses in some patients with chemotherapy-resistant locally advanced or metastatic DFSP. Wide surgical excision of the tumor is still the accepted treatment despite local recurrence rate of 20–50% in completely resected patients. The value of RT in the management is not clearly defined. We present a 39-year-old man with a 7 month history of gradually enlarging facial masses with biopsy consistent with DFSP. Head and neck CT showed a 14 × 15 × 14cm cheek mass, a chin mass of 4 × 5 × 4cm and 2 facial skin lesions below the lower lip measuring 1 cm. Chest and abdomen CT showed no metastasis and PET scan showed uptake in facial lesions only. Complete wide surgical excision was not possible. Preoperative Imatinib, 400 mg/d, was initiated and tolerated well. Methods: Weekly plasma PDGF-B levels was measured using ELISA Results: After 3 weeks, CT scan showed ∼50% reduction in the left cheek and chin tumors with near complete resolution of the facial skin lesions. PET scan showed markedly decreased uptake in both masses. Weekly measurements of plasma PDGF-B levels using ELISA decreased 4 fold over 3 weeks from 1050pg/ml, 690pg/ml to 270pg/ml correlating with clinical response, which has not been previously reported. Further studies are ongoing in this and other patients. Conclusions: This case shows the potential use of imatinib as neoadjuvant treatment in DFSP, and the potential value of measuring serial PDGF-B levels as a novel tumor marker not only in DFSP but perhaps in all tumors that depend on the PDGF-B pathway. No significant financial relationships to disclose.