CD34-negative solitary fibrous tumour resistant to imatinib

A 75-year-old man presented to our hospital with multifocal thickening of the left pleura and left pleural effusion. Histology of the pleura showed uniform and bipolar spindle cells with moderate mitosis in a collagenised stroma. It further showed abundant blood vessels in a haemangiopericytoma-like pattern. These findings were strongly suggestive of malignant solitary fibrous tumour (SFT). The tumour showed negative staining for CD34. The loss of CD34 expression could imply histologically high-grade tumour, as reported previously. Imatinib, a multityrosine kinase inhibitor with targets, including platelet-derived growth factor receptor (PDGFR)-α and PDGFR-β, has antitumour activity in some patients with SFT. Unfortunately, imatinib treatment failed to control disease progression in the present case that expressed PDGFR-β, but not PDGFR-α. This report described a case of CD34-negative SFT resistant to imatinib.