Abstract
Solitary fibrous tumor (SFT) is a mesenchymal neoplasm of fibrous origin. The 2013 WHO classification of soft tissue tumors defines malignant forms as hypercellular, mitotically active (>4 mitosis/10 high-power fields), with cytological atypia, tumor necrosis, and/or infiltrative margins. With an IRB-approved protocol, we investigated patient records and clinicopathologic data from our Sarcoma Database to describe the clinical characteristics of both benign and malignant SFT. All pathology specimens were reviewed by two pathologists. Descriptive statistics and univariate/multivariate survival analysis were performed. Patient records and Social Security Death Index were used to evaluate vital status. Of 82 patients, 47 (57%) were women and 73 (89%) were Caucasian. Median age was 62 years (range, 20 to 89). Thirty-two (39%) patients succumbed to the disease. Primary tumor site was lung/pleura in 28 (34%), abdomen/pelvis in 23 (28%), extremity in 13 (16%), and head/neck in 9 (11%) patients. Pathology was described as benign in 42 (51%) and malignant in 40 (49%) patients. Compared to benign SFT, malignant histology is associated with larger tumor size, higher mitotic counts, metastatic disease at diagnosis, and greater use of chemotherapy and radiation therapy. Gender, age, and tumor site were not significantly different between benign and malignant subtypes. By univariate analysis, only benign vs. malignant variant and complete resection positively impacted overall survival (P = 0.02 and P<0.0001, respectively). In the multivariable analysis of overall survival, receiving chemotherapy or not receiving surgery were two variables significantly associated with higher failure rate in overall survival: patients with chemotherapy vs. no chemotherapy (P = 0.003, HR = 4.55, with 95% CI: 1.68–12.34) and patients without surgery vs. with surgery (P = 0.005, HR = 25.49, with 95% CI: 2.62–247.57). Clear survival differences exist between benign and malignant SFT. While surgery appears to be the best treatment option for benign and malignant SFT, better systemic therapies are needed to improve outcomes of patients with metastatic, malignant SFT.
Highlights
Solitary fibrous tumor (SFT) is a mesenchymal tumor of fibroblastic type that is poorly understood
England et al determined benign versus malignant characteristics in pleural SFT, followed by Vallat-Decouvelaere et al who first distinguished malignant from benign variants of extrapleural SFT on the basis of nuclear atypia, hypercellularity, greater than 4 mitosis/10 high-power fields, and necrosis. [7, 8] The 2013 WHO classification of soft tissue tumors further defines malignant forms as hypercellular, mitotically active (>4 mitosis/10 high-power fields), with cytological atypia, tumor necrosis, and/or infiltrative margins. [1]
Many patients do not respond to chemotherapy. [11,12,13,14,15] One recent retrospective study evaluated the efficacy of temozolomide and bevacizumab to treat advanced/metastatic SFT and noted that response, as defined by Choi criteria, correlates with improved progression-free survival compared to non-responders
Summary
Solitary fibrous tumor (SFT) is a mesenchymal tumor of fibroblastic type that is poorly understood. [7, 8] The 2013 WHO classification of soft tissue tumors further defines malignant forms as hypercellular, mitotically active (>4 mitosis/10 high-power fields), with cytological atypia, tumor necrosis, and/or infiltrative margins. [6, 9, 10] In patients with distant metastases or local recurrences after resection, options are limited and have mostly been studied in meningeal disease. [11,12,13,14,15] One recent retrospective study evaluated the efficacy of temozolomide and bevacizumab to treat advanced/metastatic SFT and noted that response, as defined by Choi criteria, correlates with improved progression-free survival compared to non-responders. [16] a prospective trial was presented at AACR in 2010 that examined the molecular characteristics and targeted therapeutics for patients with SFT resistant to conventional chemotherapies. Further study is still needed, but these therapies showed promise in these patients. [18]
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