Molecular T argeting o f P latelet-Derived G rowth F actor B by I matinib M esylate i n a P atient W ith M etastatic Dermatofibrosarc oma P rotuberans

Purpose: Dermatofibrosarcoma protuberans is caused by activation of the platelet-derived growth factor B (PDGFB) receptor, a transmembrane tyrosine kinase. We investigated the response of dermatofibrosarcoma protuberans to the tyrosine kinase inhibitor imatinib mesylate. Patients and Methods: A patient with unresectable, metastatic dermatofibrosarcoma protuberans received imatinib mesylate (400 mg bid). Response to therapy was assessed by [ 18 F]fluorodeoxyglucose (FDG) positron emission tomography, magnetic resonance imaging, and histopathologic and immunohistochemical evaluation. Results: The patient was treated for 4 months with imatinib mesylate. The hypermetabolic uptake of FDG fell to background levels within 2 weeks of treatment, and the tumor volume shrank by over 75% during the 4 months of therapy, allowing for resection of the mass. There was no residual viable tumor in the resected specimen, indicating a complete histologic response to treatment with imatinib mesylate. Conclusion: Imatinib mesylate is highly active in dermatofibrosarcoma protuberans. The dramatic response seen in this patient demonstrates that inhibition of PDGFB receptor tyrosine kinase activity can significantly impact viability of at least one type of solid tumor. J Clin Oncol 20:3586-3591. © 2002 by American Society of Clinical Oncology.