Changing epidemiology of gastric sarcomas in the United States.

Abstract

47 Background: The introduction of imatinib as targeted therapy for the treatment of gastrointestinal stromal tumors (GIST) has supplied a strong impetus for the reclassification of gastric sarcomas (GS). We examined the changes in the incidence and mortality over the last 20 years for GS subtypes using the Surveillance, Epidemiology, and End Results (SEER) database over the last 20 years. Methods: Based on information from SEER, GS cases were identified by primary cancer site and ICD-O-3 codes. SEER*stat was used to make estimates of incidence and cause specific survival. Joinpoint software was used to test for trends. Results: The overall incidence of GS increased of from 1991 and to 2011 from 2.9 (standard error [SE] 0.4) to 6.6 (SE 0.6) cases per million per year. The histologic subtypes of changed over this time interval with the leiomyosarcoma being initially the leading GS subtype with an incidence from 2.3 (SE 0.4) decreasing to 0.1 (SE 0.1). The incidence of gastric GIST increased from 0.1 (SE 0.1) to 6.3 (SE 0.6) representing 95% of all GS cases in 2011. For GS test for trend with Joinpoint model did not detect a discontinuity in the trend (occurring at a rate of 4.7% [p < 0.001]) relative increase per year. Much of the total GS increase in incidence was for localized disease with the incidence rates which increased from 1.2 to 4.5 cases per 10^6/year a relative increase of 6.8% (p < 0.01) per year. During this period the 3-year cause specific mortality improved for localized GS from 9.4% to 0.9%. Improvements were also seen for mortality outcomes for regional and distant disease. Conclusions: Between 1991 and 2011, more than a doubling of incidence of GS was observed with a concurrent rapid change in GIST - most in localized disease and a dramatic improvement in its outcome. It seems unlikely that this is due to changes in the underlying biology of the disease, or to imatinib alone, but may be, in part, due to changes in diagnostic techniques or pathologic evaluation