Immunohistochemical and Biogenetic Features of Diffuse-Type Tenosynovial Giant Cell Tumors: The Potential Roles of Cyclin A, P53, and Deletion of 15q in Sarcomatous Transformation

Purpose: Diffuse-type tenosynovial giant cell tumor (D-TSGCT) is an aggressive proliferation of synovial-like mononuclear cells with inflammatory infiltrates. Despite the COL6A3-CSF1 gene fusion discovered in benign lesions, molecular aberrations of malignant D-TSGCTs remain unidentified. Experimental Design: We used fluorescent in situ hybridization and in situ hybridization to evaluate CSF1 translocation and mRNA expression in six malignant D-TSGCTs, which were further immunohistochemically compared with 24 benign cases for cell cycle regulators involving G 1 phase and G 1 -S transition. Comparative genomic hybridization, real-time reverse transcription-PCR, and a combination of laser microdissection and sequencing were adopted to assess chromosomal imbalances, cyclin A expression, and TP53 gene, respectively. Results: Five of six malignant D-TSGCTs displayed CSF1 mRNA expression by in situ hybridization, despite only one having CSF1 translocation. Cyclin A ( P = 0.008) and P53 ( P P TP53 gene, which was validated by an antibody specifically against wild-type P53 protein. Chromosomal imbalances were only detected in malignant D-TSGCTs, with DNA losses predominating over gains. Notably, −15q was recurrently identified in five malignant D-TSGCTs, four of which showed a minimal overlapping deletion at 15q22-24. Conclusions: Deregulated CFS1 overexpression is frequent in malignant D-TSGCTs. The sarcomatous transformation involves aberrations of cyclin A, P53, and chromosome arm 15q. Cyclin A mRNA is up-regulated in malignant D-TSGCTs. Non–random losses at 15q22-24 suggest candidate tumor suppressor gene(s) in this region. However, P53 overexpression is likely caused by alternative mechanisms rather than mutations in hotspot exons.