[113] Solitary Fibrous Tumor of the Retroperitoneum and Abdomen/Pelvis: A Clinicopathological, Immunhistochemical and Cytogenetic Analysis of 29 Cases

GJ Smalberger, G Mann, BL Hoch. University of Washington, Seattle, WA

Background: Solitary fibrous tumor of the retroperitoneum and abdomen/pelvis (SFT-RAP) represents 9-24% of extrathoracic SFTs. SFT-RAPs comprise a large proportion of reported cases with atypical/malignant features. We performed a clinicopathological, immunohistochemical and cytogenetic analysis of a large series of SFT-RAPs.
Design: Twenty-nine cases of SFT-RAP were retrieved from our files. Cases were examined for size, growth pattern, cytological atypia, cellularity, mitotic activity, necrosis, and unusual features. Immunohistochemical stains were performed using the avidin-biotin-peroxidase complex technique. Follow-up information was obtained from the medical record.
Results: Patients ranged in age from 25-79 (ave=57) years. 62% were female and 38% male. 12 cases arose in the retroperitoneum and 17 in the abdomen/pelvis. Grossly, all tumors were solitary and circumscribed except for 2 cases that had infiltrative margins and 1 that presented as multiple mesenteric nodules. Average tumor size was 12.1 (range 5-25) cm. 64% of cases measured greater than 10cm. Myxoid change was present in 35% of cases (5-95% of tumor). Lipomatous metaplasia was seen in 3 cases. Epithelioid cytology was evident in 4 cases. Marked stromal or perivascular hyalinization was identified in 7 cases. Striking amianthoid fibers were present in 1 case. 17 cases (59%) had at least one atypical histological feature (atypia, increased cellularity, >4 mitoses/10hpf, or necrosis). 25/28 cases were positive for CD34, 11/11 positive for CD99, and 3/4 positive for bcl-2. Rare cases showed focal staining for actin, desmin, S100, EMA, or pancytokeratin. Cytogenetic aberrations, including four cases with translocations, two of which involved 18p11.2, were identified in 5/9 cases studied. Follow-up ranging from 2-120 (ave=38) months was available in 22 cases. Seven patients developed local recurrence and/or metastasis. Six of these had atypical histological features of which 5 had increased mitoses and/or necrosis.
Conclusions: SFT-RAPs commonly have atypical/malignant histological features. Other unusual features including myxoid change, lipomatous metaplasia, hyalinization, and epithelioid cytology may be present. Cytogentic aberrations may include translocations involving 18p11.2. Similar to SFTs at other sites, the presence of atypical/malignant features is not necessarily predictive of behavior. However, tumors with increased mitoses and/or necrosis often behaved aggressively.
Category: Bone & Soft Tissue

Monday, March 22, 2010 1:00 PM

Poster Session II # 7, Monday Afternoon


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