RISK FACTORS FOR LOCAL RECURRENCE AND METASTASIS IN SOLITARY FIBROUS TUMOR

Introduction: Solitary fibrous tumor (SFT) is a rare soft tissue sarcoma, with fibroblastic differentiation. It is generally associated with low rates of local recurrence or metastasis (REC/MT). Tumor size, high mitotic rates, necrosis/hemorrhage, positive resection margins and nuclear pleomorphism are suggest to impact prognostic. However, eminent risk factors for aggressive phenotype are not well defined. Objectives: Primary objective was to analyze factors associated with REC/MT in patients (pts) with SFT. Secondary objectives were to evaluate disease free survival (DFS) in non-metastatic (non-MT) pts at diagnosis and its associated factors and to evaluate overall survival (OS). Methods: Retrospective analysis of pts diagnosed with SFT were performed in a sigle center in Brazil. Descriptive statistics were used to evaluate population characteristics and REC/MT occurrence. X² test was used to proportional comparative analysis and logistic regression to determine factors associated with REC-MTX in global population. Kaplan Meier, Log-Rank test and Cox Regression were used to survival analysis. Results: From April, 1971 to May, 2018, 86 pts were treated. Median follow-up was 6 years (y). 69 (80.2%) were alive on the cut-off date. Median age at diagnosis was 48y. 40.7% were men. Main primary sites were pleura (20.9%) and extremities (14.0%). 76 (88.4%) had surgery and 15 (17.4%) radiotherapy for the primary tumor. 34 (39.5%) had REC/MT, of whom,10 (11.6%) had MT at diagnosis. Median OS of global population was 25y (95%CI 12.2-37.7) and of REC/MT subgroup was 13y (95%CI 8.3-17.7). Tumor > 10cm and presence of any risk factor (tumor > 10cm, necrosis, positive margins or ≥ 4/10 mitosis) were associated with REC/MT in the univariate analysis. Presence of necrosis (p = 0.045) was an independent factor for REC/MT in the multivariate analysis. Considering 76 pts with non-MT disease at diagnosis, median DFS was 11y (95%CI 4.5-17.5). DFS was superior for pts without any risk factor (not reached versus 6y; HR 0.26, 95%CI 0.09-0.76; p = 0.015) and < 4/10 mitosis (not reached versus 4y; HR 0.37 95%CI 0.14-0.96). Presence of necrosis was independent associated with inferior DFS in multivariate analysis (p = 0.43). Conclusions: SFT is an indolent neoplasm, with prolonged survival even in REC/MT scenario and with long DFS, which highlights the relevance of long term follow-up of pts. Presence of necrosis were associated with development of REC/MT and poor DFS in this study.