TUMOR SIZE-RELATED DNA COPY NUMBER CHANGES OCCUR IN SOLITARY FIBROUS TUMORS BUT NOT IN HEMANGIOPERICYTOMAS

Solitary fibrous tumor (SFT) presenting in the pleura and other soft t issue sites and hemangiopericytoma (HPC) presenting at various soft ti ssue sites are mesenchymal tumors that. share many histologic and immu nohistochemical features. This raises the questions of whether these t umors are related and whether they belong within the spectrum of a sin gle biologic entity, The behavior of both SFTs and HPCs is difficult t o predict histologically, The genetic background of both SFTs and HPCs is poorly known, but it could be helpful in the evaluation of maligna ncy and could give clues to their possible relationship, In this study , we analyzed 15 SFTs and 11 HPCs by comparative genomic hybridization (CGH), a powerful molecular cytogenetic tool that can be applied to D NA extracted from formaldehyde-fixed and paraffin-embedded tissue, All of these tumors were immunohistochemically similar and showed reactiv ity for CD34-antigen but not for keratins, desmin, or muscle actins, O nly 1 SFT smaller than 10 cm showed DNA copy number changes (a single loss in chromosome 13), but 7 of 8 SFTs larger than 10 cm (including a ll 4 tumors with more than 4 mitoses per 10 high power fields) showed changes, mostly chromosomal gains in 5q 7, 8, 12, and 18. Four cases s howed losses, two of them in chromosome 13 and two others in 20q. Thes e findings suggest that CGH might be useful in the evaluation of malig nant transformation in SFT. The most common change, gain of the entire chromosome 8, seen in two cases as the only change, suggests trisomy 8 and parallels a similar finding previously described in other fibrou s tumors, such as subsets of desmoid fibromatosis and infantile fibros arcoma, In contrast, HPCs, inducting large and mitotically active tumo rs, showed no DNA copy number changes on CGH. This suggests that HPC i s genetically different from SFT.