Primary gastrointestinal stromal tumor (GIST) sited outside the gastrointestinal (GI) tract carries a poorer prognosis than primary GIST within the GI tract, according to a study presented at the recent ASCO GI Symposium in January 2012. Lead investigator of the study, Mary L. Guye, MD, surgical oncologist at the City of Hope Medical Center in Duarte, California, noted that these results suggest that GIST location should be factored into risk stratification. The reasons are unknown for the poorer prognosis in GIST sited outside the GI tract, she said, noting that molecular analysis is needed to investigate the biology of these less common GISTs to help determine why they carry a worse prognosis.
The study included 2591 patients from a SEER (Surveillance, Epidemiology, and End Results) database from 1996-2008 who underwent primary surgery for GIST. Primary tumors were located outside the GI tract (omentum, mesentery, retroperitoneum, or another location) in 10% of cases. Patients with intra-GI and extra-GI primary tumors were of similar ages and racial distribution. For the group with extra-GI primary tumors, 5-year survival was 62% versus 70% for those with tumors located within the GI tract. Median overall survival was 105 months for extra-GI tumors versus 120 months for those with tumors in the GI tract (P = .002).
Tumors sited outside the GI tract tended to be larger than 10 cm, have more advanced regional or distant disease, and were more likely to be treated with radiation therapy. In a multivariate analysis adjusting for these confounding factors, the findings remained the same. Extra-GI tumors were still associated with almost a 30% increase in mortality (P = .03). One limitation of the study is that the SEER registry does not include data on mitotic rate or on systemic medical therapies patients were taking.