Brief report: activity of imatinib in a patient with platelet-derived-growth-factor receptor positive malignant solitary fibrous tumor of the pleura.

Malignant solitary fibrous tumor (MSFT) of the pleura is a rare neoplasm, with unpredictable biologic behavior and a low sensitivity to chemotherapy. To the authors' knowledge, no other effective medical treatment is available for this disease. Imatinib mesylate is a tyrosine kinase inhibitor targeting the platelet-derived growth factor (PDGFR-alpha and PDGFR-beta), the BCR-ABL, and c-KIT receptors. We report the first evidence of the activity of imatinib in a symptomatic patient with a chemo- and radio-resistant advanced MSFT, who obtained a 21-months lasting major clinical benefit with a consistent reduction in tumor metabolism. Immunostaining of tumor cells demonstrated the positivity for PDGFR-alpha and PDGFR-beta and the absence of c-KIT over-expression, in the absence of c-KIT and PDGRFR mutations; all the cells strongly and diffusely expressed the ligand PDGF A in the cytoplasm. This profile suggests that the observed tumor response was mediated through the inhibition of the tyrosine kinase activity of PDGFR. Treatment with imatinib should be considered for patients with recurrent or unresectable MSFTs with PDGFR expression.