SAN FRANCISCO – Surgically removing residual gastrointestinal stromal tumors in patients who respond to imatinib therapy significantly increased time to tumor progression to 88 months, compared with 43 months using imatinib alone, based on findings from a retrospective study of 134 patients.
After controlling for the effects of other risk factors, the surgery decreased threefold the likelihood of disease progression and decreased fivefold the risk of death, Dr. Seong Joon Park reported in a press briefing sponsored by the American Society of Clinical Oncology (ASCO). The press conference was held in advance of at a meeting on gastrointestinal cancers sponsored by ASCO and three other cancer organizations.
The findings support the widely adopted practice of removing residual tumors in these patients, despite the retrospective and observational design of the study, Dr. Park said. A prospective European study of similar design to this one terminated early due to poor patient enrollment. "It’s really hard to conduct a prospective study of this design," said Dr. Park of Asan Medical Center, Seoul, South Korea.
He and his associates reviewed the records of patients who showed at least 6 months of disease stabilization or response to imatinib (Gleevec) treatment, 92 of whom got the drug treatment alone and 42 of whom underwent surgery to remove residual tumors after a median of 19 months of imatinib therapy. The imatinib therapy was restarted after surgery. Median follow-up for the cohort as a whole was 59 months.
"This treatment strategy is worth trying as a clinical practice if the medical center is large enough to have an experienced multidisciplinary team and to have low morbidity and mortality associated with surgery," he said.
Each year, approximately 5,000 new cases of gastrointestinal stromal tumors are diagnosed in the United States, most often in the stomach and small intestine, though they can occur anywhere in or near the GI tract. Imatinib typically is first-line therapy, and 80%-85% of patients will respond to the treatment, he said. A majority of patients who respond to imatinib will have residual tumors, however, which are believed to contribute to the development of drug resistance, leading to the hypothesis that removing the residual tumors would improve survival.
In general, one-third of patients are candidates for surgical removal of residual lesions, depending on the tumor size and other tumor and patient characteristics, Dr. Park said.
The two patient groups in the study were similar except that the surgery group was significantly younger (51 vs. 58 years) and was less likely to have metastases in the peritoneum (41% in the surgery group vs. 61% in the control group).
As it is an aggressive and difficult treatment, surgery is more likely to be considered and recommended to younger patients who have a good performance status and, thus, less likely to be recommended in patients with multiple peritoneal metastases.
Factors associated with longer progression-free and overall survival included surgery and having an initial tumor size less than 150 mm, multivariate analyses showed. Female sex and having the KIT exon 11 mutation also were associated with longer progression-free survival. The researchers used propensity scores and inverse-probability-weighting adjustments to account for the effects of factors other than surgery.
The gastrointestinal cancers meeting, where Dr. Park will present the results, is cosponsored by ASCO, the American Gastroenterological Association Institute, the American Society for Radiation Oncology, and the Society of Surgical Oncology.
Dr. Park reported having no financial disclosures.
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