SAN FRANCISCO – Patients with gastrointestinal stromal tumors have a poorer prognosis if their primary tumor is located outside the gastrointestinal tract, researchers reported.
In an analysis of a U.S. population–based cohort of 2,591 patients who underwent surgery for gastrointestinal stromal tumors (GIST), 10% had primaries in the omentum, mesentery, retroperitoneum, or another location separate from the tubular gastrointestinal tract.
The 5-year overall survival rate for this group of patients with extragastrointestinal stromal tumors (EGIST) was 62%, which was significantly poorer than the 70% observed for those with primaries in the typical gastrointestinal tract location, mainly the stomach or small intestine.
Patients with primaries outside the gastrointestinal tract had larger tumors and more advanced stage, the study found. But even after adjustment for these potential confounders, extragastrointestinal location was still associated with a nearly 30% increase in the risk of death.
"The results of our study suggest that tumor location outside the gastrointestinal tract should be considered as an important variable, and risk stratification for prognosis should account for these rare GIST locations," said lead investigator Dr. Mary L. Guye, who presented the data at the gastrointestinal cancers symposium sponsored by the American Society of Clinical Oncology.
The reason for this poorer prognosis is unknown, said Dr. Guye, a surgical oncologist at the City of Hope National Medical Center in Duarte, Calif.
"It could be these are truly metastatic foci with an unidentified or unknown primary tumor, or they may simply be more aggressive tumors that arise de novo outside the gastrointestinal tract," she proposed, calling for further studies to investigate the tumor biology of these rare GIST tumors.
"Evaluation of histology, looking at tumor mitotic rate, and also mutational analyses may help to determine why extra-intestinal location confers a worse prognosis for GIST tumors," she said.
In an interview, Dr. Allan Pickens of Emory University in Atlanta, cochair of the scientific session in which the data were presented, said, "This was a great study [that further defined] the difference between the traditional GISTs that we treat more commonly and the ones that are outside of the gastrointestinal tract [and] have a worse prognosis."
Dr. Pickens agreed that molecular analyses will help better define how the two groups of tumors differ. "It would be interesting to see some of the microRNA information applied to those different tumors to see if it could predict those worse outcomes," he said.
Dr. Guye and her colleagues analyzed SEER (Surveillance, Epidemiology, and End Results) data for 1996-2008 to identify their study population with GIST, choosing the start year because that is when diagnosis of this tumor became more accurate, she explained.
Patients with primaries in and outside the gastrointestinal tract had similar age and racial distribution. But patients with EGIST were more likely to receive radiation therapy, to have tumors larger than 10 cm, and to have regional or distant disease.
Median overall survival was 120 months in the group with primaries in the gastrointestinal tract, and 105 months in the group with primaries in other locations (P = .002).
Additional analyses showed that location outside the gastrointestinal tract conferred a worse prognosis, even when tumors were matched for size and stage of disease, Dr. Guye reported. And the association stood up in multivariate analysis (P = .03).
However, "the SEER database does not include information on mitotic rate or information on systemic medical therapies," she noted. "Therefore, we were not able to include these factors in our analysis."
Dr. Guye and Dr. Pickens disclosed that they had no relevant conflicts of interest.