Complete response to imatinib in relapsing pigmented villonodular synovitis/tenosynovial giant cell tumor (PVNS/TGCT).

letters to the editor Complete response to imatinib in relapsing pigmented villonodular synovitis/tenosynovial giant cell tumor (PVNS/TGCT) Pigmented villonodular synovitis (PVNS), also known as tenosynovial giant cell tumor (TGCT), is a rare pathological entity affecting the synovium in young adults [1, 2]. Initially considered as an inflammatory reactive process, recent observations have shown that this disease may actually be a benign neoplastic process with specific genetic alterations [3, 4]. Indeed, a specific t(1;2) translocation, involving the collagen 6A3 gene (on 2q35) and the macrophage colony-stimulating factor (M-CSF) (also known as CSF1) gene (on 1p13), is present in a fraction of tumor cells in PVNS/TGCT. This fusion gene expressed by a fraction of the cells encodes for a fusion protein which attracts non-neoplastic cells expressing Macrophage colony stimulating factor (M-CSFR), through a paracrine—'landscape'—effect [3, 4]. PVNS/TGCT is generally treated by surgery alone. However, relapses may occur, and re-excision may be needed, with possible important functional impairment [1, 2]. In addition to its inhibitory activity on BCR-ABL, KIT, and platelet derived growth factor receptor alpha, imatinib has recently been reported to block M-CSFR activation at therapeutic concentration [5]. These observations prompted us to evaluate imatinib in a patient with recurrent and symptomatic PVNS/TGCT following surgery, in whom surgical re-excision would have had important functional consequences. A 34-year-old right-handed female was referred to us for a rapid painful relapse of PVNS/TGCT of the right elbow 3 months after surgical removal of the lesion. Imatinib was initiated at a dose of 400 mg/day on 18 September 2006 (Figure 1). A partial response was observed at month 2 (08 November 2006) and complete remission was observed at month 5 (28 February 2007). Treatment was interrupted at month 7. In June 2007 (month 9), a symptomatic painful relapse of the tumor was diagnosed both clinically and on magnetic resonance imaging. Imatinib was reintroduced at the same dose and a second complete remission was observed in September 2007 and confirmed in December 2007 at month 14. The rationale for imatinib treatment in this observation came out from the hypothesis that imatinib may disrupt the paracrine loop found responsible for PVNS/TGCT growth [3, 4, 6]. In this patient, the rapid response observed with imatinib, Figure 1. Response to imatinib in PVNS.