Gastrointestinal stromal tumor (GIST) of the rectum and pararectal space: A French Sarcoma Group (FSG) retrospective review.

Abstract

10055 Background: GIST of rectum and pararectal space are rare entities with limited clinicopathologic series reported. We conducted a retrospective analysis of rectal GIST during the past 9 years in FSG centers. Methods: Patients (pts) with rectal GIST cases were identified in two ways: (1) advanced/metastatic rectal/pararectal GISTs enrolled in the BFR14 trial (36 pts); and (2) a separate group of 45 pts reported via survey from 14 FSG centers. Results: Characteristics for the BFR14 group showed male predominance (57%), median age 62 years, majority of pts (68%) had metastatic GIST. All pts received imatinib (IM), 65% underwent resection of the primary tumor. With a median follow up (FU) of 29 months, the 2-years PFS and OS are 58% and 87% respectively. In the survey group, all rectal GISTs were localized except 5 with metastatic disease. Men were predominant (66%), tumors ranged from asymptomatic (discovered incidentally in 9 pts), to large masses causing pelvic symptoms (pain, bleeding, constipation; in 28 pts), median tumor size was 65 mm (6-130). Twelve pts received preoperative IM therapy (median duration 7 months; 2-10); 8 (67%) experienced PR, 3 minor responses and one had SD. IM treatment allowed sphincter conservation in 7 cases. 40/45 pts underwent surgery. Anterior resection was performed in 13 pts, transanal/transperineal resection in 13 pts, and amputation in 11 pts. Tumor resections were mostly R0/R1 (22/13, 87%), without tumor rupture (72%). 13 tumors had ≤ 5 mitotic index and 21 had >5 mitotic index. Mutations, mostly in exon 11, were documented in 9 of 12 cases. Ten pts received adjuvant IM. With a median FU of 55 months (1-170), 10 pts have died. Twenty pts (50%) developed local recurrence [18 (72%) after surgery alone, 2 (13.5%) after resection combined with preoperative ± postoperative IM], and 8 secondary metastases, in a median of 17 months (5- 87). Conclusions: Preoperative IM treatment results in substantial tumor shrinkage in most pts and facilitates function-preserving surgery. Since rectal GISTs have a high risk for local relapse, postoperative IM should be systematically considered for these pts. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis, Pfizer, PharmaMar Amgen, Novartis, Pfizer, PharmaMar Bayer