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Background: After a huge efficacy of imatinib in treating patients with gastrointestinal stromal tumors (GISTs) was proven, a maximum effort was made to make a differential diagnosis between GISTs and gastrointestinal leiomyosarcomas (GI‐LMS), showing the latter to be an extremely rare tumor entity. Limited data on GI‐LMS biology, clinical behavior and drug‐sensibility are available, and the clinical decision‐making in this subgroup of patients is usually challenging. Methods: We conducted a multicenter, retrospective observational study on patients with diagnosed GI‐LMS from 2004 to 2020 within six high‐volume referral centers in Italy. Results: Thirty‐three patients had diagnosis of KIT‐negative GI‐LMS confirmed by sarcoma‐expert pathologist. The most common site of origin was the intestine. Twenty‐two patients had localized disease and underwent surgery: with a median follow‐up of 72 months, median disease‐free survival was 42 months. Overall survival (OS)‐rate at 5 years was 73% and median OS was 193 months. Five out of 10 patients with local relapse received a salvage surgery, and 2/5 remained with no evidence of disease. Thirteen patients received neoadjuvant (6) or adjuvant (7) chemotherapy, and 2/13 patients remained free from relapse. The median OS for patients with metastatic LMS was 16.4 months. Conclusion: GI‐LMS is very rare and extremely aggressive subgroup of sarcomas with a high tendency to systemic spread. Localized GI‐LMS at diagnosis may be cured if treated with adequate surgery with or without (neo) adjuvant chemotherapy, while de‐novo metastatic disease appeared to have a poor prognosis. Clinical effort to understand GI‐LMS biology and clinical behavior and to develop active treatment strategy, especially for metastatic‐disease, is warranted. [ABSTRACT FROM AUTHOR]

To investigate the activity of regorafenib in advanced solitary fibrous tumour (SFT). An Italian monocentric investigator-initiated exploratory single-arm Phase II trial was conducted of regorafenib in adult patients with advanced and progressive SFT, until progression or limiting toxicity. Prior treatment with antiangiogenics was allowed. Primary and secondary end-points were: overall response rate (ORR) by Choi criteria, and ORR by RECIST, progression-free survival (PFS), overall survival (OS). From January 2016 to February 2021, 18 patients were enroled [malignant-SFT = 13; dedifferentiated-SFT (D -SFT) = 4; typical-SFT (T-SFT) = 1]. Fourteen patients were pre-treated, in 12 cases with antiangiogenics (median [m-] lines of treatment = 3). Sixteen patients were evaluable for response (one screening failure; one early discontinuation). Six/16 (35.2%) required a definitive dose reduction. ORR by Choi was 37.5% (95% CI: 15.2–64.6), with 6/16 (37.5%) partial responses (PR), 6/16 (37.5%) stable disease (SD) and 4/16 (25%) progressions; 5/6 responses occurred in patients pre-treated with antiangiogenics. No responses were detected in D -SFT. Best RECIST responses were: 1/16 (6.2%) PR, 12/16 (75%) SD, 3/16 (18.8%) progressions. At 48.4 month m-FU, m-PFS by Choi was 4.7 (inter-quartile range: 2.4–13.1) months, with 31.2% patients progression-free at 1 year. Regorafenib showed activity in SFT, with 30% patients free-from-progression at one year. Responses were observed also in patients pretreated and refractory to another antiangiogenic agents. However, ORR and m-PFS were lower than reported with other antiangiogenics, and this was possibly due to discrepancies in the patient population and the high-rate of dose reductions. • Regorafenib (R) is active in advanced, progressive solitary fibrous tumour (SFT). • R activity was seen in typical-/malignant-SFT but not in dedifferentiated-SFT. • R was effective also in cases refractory to previous antiangiogenic agents. [ABSTRACT FROM AUTHOR]