Abstract 5909: The role of overdiagnosis & better diagnosis of low-lethality disease in the rising incidence of cancer of the small intestine
Authors: Yao Haley J. , Sokas Claire , Welch H. Gilbert 
Published: June 2022

Abstract
Despite accounting for &gt;90% of the surface area of the GI tract, the small intestine has historically been responsible for &lt;5% of all GI cancers. Over time, however, the incidence of small intestinal cancer has increased while other GI cancers (eg., colorectal, gastric, etc.) have decreased. To help elucidate the cause of this increase, we investigated histology-specific incidence and mortality trends in small intestinal cancer. We used SEER-9 data (covering ~10% of the US population) to identify 4 histological categories of small intestinal cancers (adenocarcinoma, neuroendocrine, lymphoma, and sarcoma/gastrointestinal stromal tumor [GIST]) to assess trends in incidence. Because death certificates do not include histology information, incidence-based mortality (IBM) was used to assess histology-specific mortality trends. From 1976 to 2016, 22,082 patients were diagnosed with one of four histological types of small intestinal cancer (ICD-O-3 codes C17.0-17.9). The overall incidence of these cancers more than doubled, from 12.1 to 27.9 per million (absolute increase 15.8; 95% CI: 14.3-17.3), largely because of a nearly 4-fold growth in neuroendocrine tumor incidence: from 3.7 to 14.6 per million (absolute increase 10.9; 95%CI: 10.0-11.8). The proportion of patients with localized disease increased from 14.7% of cases in 1976 to 38.9% of cases in 2014. There was little concomitant change in neuroendocrine mortality (from 1.4 to 2.2 per million, absolute increase 0.8; 95%CI: 0.4-1.2). The histologic distribution changed from 30% neuroendocrine histology in 1976 to 52% in 2016. Duodenal neuroendocrine tumors grew particularly rapidly from 0.1 to 4.2 per million (absolute increase 4.1; 95% CI, 3.7-4.5). Adenocarcinoma incidence rose slightly, but in tandem with mortality. Deaths attributed to small intestinal cancer on death certificates were virtually indistinguishable from adenocarcinoma IBM, suggesting that deaths attributed to small intestinal cancer were, in fact, predominantly due to adenocarcinoma. Both incidence and mortality of lymphoma initially rose before declining, similar to that for non-Hodgkin’s lymphomas in general. Despite a small increase in GIST incidence, mortality decreased by 40% (from 1.0 to 0.6 per million). In summary, cancers of the small intestine are being diagnosed more frequently. There was little change in the occurrence of adenocarcinoma or the ability to treat the disease. Treatment advances, however, were apparent in GIST and lymphoma as evidenced by improvements in population-based mortality. Neuroendocrine tumor incidence increased rapidly and substantially while mortality was relatively stable, a pattern consistent with overdiagnosis and/or better diagnosis of symptomatic, low-lethality disease. Overdiagnosis appeared particularly likely in early stage and (more accessible) duodenal tumors.
Citation Format: Haley J. Yao, Claire Sokas, H. Gilbert Welch. The role of overdiagnosis & better diagnosis of low-lethality disease in the rising incidence of cancer of the small intestine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5909.