Pleuro-pulmonary solitary fibrous tumors: A clinicopathologic, immunohistochemical, and molecular study of 88 cases confirming the prognostic value of de perrot staging system and p53 expression, and evaluating the role of c-kit, BRAF, PDGFRs (α/β), c-met, and EGFR

Pleuro-pulmonary solitary fibrous tumor (SFT) is a relatively uncommon mesenchymal neoplasm of uncertain histogenesis, unknown molecular features, and unpredictable clinical behavior. Although complete resection is universally accepted as the most important single prognostic factor, some clinicopathologic characteristics (gross appearance, tumor size, mitotic index, tumor necrosis, hypercellularity, and pleomorphism) are related to patient outcome, and a staging system based on these parameters with practical therapeutical implications has been recently proposed by de Perrot et al. Here, 88 pleuro-pulmonary SFTs were collected and clinicopathologic characteristics including de Perrot classification, patients' follow-up, p53 expression, and several "targetable" kinases [c-kit, v-raf murine sarcoma viral oncogene homolog B1, platelet-derived growth factor receptor (PDGFR)-alpha/beta, c-met, epidermal growth factor receptor (EGFR)] were retrospectively analyzed. Fifty-two cases (59%) had at least 1 clinicopathologic feature related to malignancy, whereas mortality and recurrences occurred in 10.2% and 18.2% of the cases, respectively. de Perrot staging and high p53 expression were significantly related to the conventional clinicopathologic prognostic features as well as to overall survival (OS) and disease-free survival (DFS) (P<0.001). At multivariate analysis, high p53 expression and tumor necrosis were the only parameters significantly associated with OS and DFS (P=0.017 and P=0.012, respectively). Immunohistochemical expression was frequently detected for PDGFR-alpha (97.7%), PDGFR-beta (86.5%), and hepatocyte growth factor receptor (96.6%), whereas missense mutations were only identified in 2 cases both involving PDGFR-beta (exons 18 and 20). We conclude that de Perrot stratification of SFT is a reliable prognostic indicator and merits consideration in view of its suggestions for the management of these tumors in daily practice. p53 expression may represent a valid and easy-to-test prognostic factor significantly related to OS and DFS. Although mutations of the corresponding genes are rare events in SFT, PDGFR-alpha/beta, and hepatocyte growth factor receptor tyrosine kinases should be further investigated given the availability of specific inhibitory molecules which might provide useful and novel therapeutical approaches for SFT patients.