Localized gastrointestinal stromal tumor of the rectum: An uncommon primary site with prominent disease and treatment-related morbidities.

Well-established clinicopathological variables used in the risk stratification of gastrointestinal stromal tumor (GIST) may not completely predict rectal GIST, an uncommon and poorly studied GIST subset. The aim of the present study was to determine the patterns of relapse and morbidities associated with recurrence in rectal GIST. A single-institution retrospective study between 2002 and 2011 was conducted, identifying 9 patients (8%) with localized rectal GIST, while comparing small intestinal (n=37) and gastric (n=63) GIST (median age, 60 years). Rectal GIST tumors were smaller compared to small intestinal/gastric GIST (P=0.044). The number of mitoses per 50 high-power field (HPF) did not differ by primary site. In general, 73% of patients were high-risk, as defined by the National Institutes of Health (NIH) consensus criteria, however, only 25% received adjuvant imatinib. Fewer rectal GIST patients achieved negative surgical margins compared to small intestinal/gastric GIST (67 vs. 92%; P=0.054). Of the 9 patients with localized rectal GIST 6 had peri-operative tumor rupture, anastomotic breakdown or required anal sphincter-compromising surgery. At the time of the first relapse, 83% of the recurrences were local failures for rectal GIST, compared to 21% for small intestinal/gastric GIST (P=0.005). The median relapse-free survival was 51 months for the entire cohort, and 54, 36 and 56 months for rectal, small intestinal and gastric GIST, respectively (P=0.468). Rectal GIST was found to be associated with high rates of local relapse and significant morbidity, despite being significantly smaller compared to GIST of other sites. A multimodality peri-operative therapeutic approach may be required to improve outcomes.