Atypical and Malignant Solitary Fibrous Tumors in Extrathoracic Locations

Abstract

Solitary fibrous tumor (SFT), first described as a pleural lesion, has been reported at numerous extrathoracic sites over the past 10 years. About 10% to 15% of intrathoracic SFTs are histologically or clinically malignant, but such cases have very rarely been described at other locations. Among 92 cases of extrathoracic SFT in our files, we identified 10 that either had recurred (2 cases) or had a least one atypical histologic feature (8 cases). The ten tumors occurred in five men and five women, 32 to 81 years old (median 56), measured 1.9 cm to 20 cm (median 11.5 cm), and were located in the abdomen/pelvis (4 cases), retroperitoneum (3 cases), groin, trunk, and upper arm. Nuclear atypia (8 cases), markedly increased cellularity (6 cases), areas of necrosis (4 cases), and greater than 4 mitoses/10 HPFs (3 cases) were seen in addition to the typical histologic features of SFT. Six tumors had at least two of these atypical histologic features. Nine cases were positive for CD34, six were positive for O-13, and one was focally positive for smooth muscle actin. Eight were excised completely. Subsequent follow-up revealed tumor relapse in eight cases (follow up 6-180 months, median 24). Four patients had local recurrence at 12 to 168 months. Distant metastasis developed at 1 to 6 years in five cases with spread to lung (2 cases), liver (4 cases), and bone. Metastasis or local recurrence developed within 2 years in five patients. To date, no patient has died of their tumor. These findings demonstrate that nuclear atypia, hypercellularity, greater than 4 mitoses/10 HPFs, and necrosis may be seen in up to 10% of extrathoracic SFTs, and are associated with, but are not by themselves predictive of, aggressive clinical behavior. In addition, our findings confirm that the behavior of extrathoracic SFTs is unpredictable, entirely comparable to that of their better known pleural counterparts, and confirm that patients with SFTs in all locations require careful, long-term follow up. It is probably unwise to regard any such lesion as definitely benign.

Solitary fibrous tumor: a clinicopathological study of 110 cases and proposed risk assessment model

“…18 In another large study of 92 extrathoracic solitary fibrous tumors, 5 of 10 cases with atypical features metastasized and an additional 3 tumors locally recurred; clinical follow-up was not provided for the remaining 82 tumors. 11 Our findings of a poor 10-year disease-specific survival of 73% is likely due to referral bias at a major sarcoma treatment center with a population skewed toward more aggressive tumors. In fact, our rates are in keeping with those reported specifically for cases historically diagnosed as hemangiopericytoma and malignant solitary fibrous tumor.…”

“…McMaster et al found that B10% of metastases occurred after 5 event-free years, while Vallat-Decouvelaere et al found that 40% of metastases occurred after 5 years. 11,16 Consequently, studies with short followup may not accurately reflect metastatic potential of tumors with malignant histological features, 7 although even in studies with longer follow-up, tumors defined as malignant using historical criteria did not metastasize. 19 In our study, 50% of metastases occurred after 36 months, but could present up to 19 years after initial resection.…”

Large solitary fibrous tumor of the oral cavity—Report of a case

“…In contrast, malignant and metastatic SFTs have been reported to occur in extraoral sites. Vallat-Decouveleare et al [23] and Gold et al [25] found local recurrence in 4.3% and 6.7% and metastases in 5.4% and 5.3%, respectively. Sites of distant metastases were lung, liver, bones, mesentery, mediastinum and retro-peritoneum [7].…”

“…This tumor usually shows increased cellularity, at least focally moderate to marked cytological atypia, areas of necrosis, numerous mitoses (>4 mitoses/10 high-power fields) and/or infiltrative margins [2,19,23]. Malignant SFT exhibits histologic features resembling malignant FH, malignant hemangiopericytoma, or fibrosarcoma.…”

Practical Issues for Retroperitoneal Sarcoma

“…115,116 Tumor cells are typically positive for CD34 (80%-90%), CD99 (70%), BCL2 (30%), epithelial membrane antigen (30%), and actin (20%). [117][118][119][120][121][122][123] Desmin, cytokeratin, and S100 are usually absent. 117 Recently, NAB2/STAT6 was identified in solitary fibrous tumors, strongly suggesting that this type of tumor is a translocation-associated neoplasm and that STAT6 immunostain is a sensitive and specific marker for solitary fibrous tumor.…”