Incidence and treatment outcomes of small cell carcinoma of the small intestine, colon, and rectum.

e15682 Background: Small cell carcinoma (SCC) of gastrointestinal tract is a highly aggressive rare malignancy with an estimated prevalence of 0.1% to 1% of all GI neoplasms. Treatment and survival outcomes data are very limited. Here we present an analysis of outcomes of patients with intestinal SCC using data from the Survival, Epidemiology, and End Result (SEER) database. Methods: SEER (2000-2020) was used to identify patients with SCC involving of the small intestine, colon and rectum. Variables included age, race, site, stage, chemotherapy (chemo), radiation therapy (RT) and surgery. Cox regression was used to model survival outcomes based on site, stage, and treatment received in the overall group and stage subgroups. Results: 1,169 patients with SCC of the small intestine, colon, and rectum were identified. Median age was 65 (24-90). 631 (54%) were male; majority of patients were white (989; 85%), followed by black (128; 11%) and other races (50; 4.3%). Colon (569; 49%) and rectum (514; 44%) were the predominant sites while small intestine only comprised 7.4% of the patients. Distant, regional and local diseases were reported in 55%, 17% and 7.5% of the patients. Median overall survival (mOS) of the entire group was 8 months (m). Primary tumor sites of small intestine and rectum were significantly associated with lower mortality rate in comparison to colon (11 m and 9 m vs 5 m, p < 0.001 for both). Patients with localized disease had the lowest mortality rate when compared with those with regional or distant metastatic diseases (38 m vs. 16 m and 5 m, p < 0.001 for both). Receiving surgery (HR: 0.458, p < 0.001), chemo (HR: 0.473, p < 0.001), and RT (HR: 0.733, p = 0.003) were all significantly associated with lower mortality rate (Table). These differences remained significant in each stage-based subgroup except for chemotherapy in localized disease subgroup, which encompassed only 87 patients. Conclusions: Intestinal SCC has poor prognosis, with SCC of the colon being most prevalent and with the highest mortality. Majority of patients presented with distant metastatic disease which led to high mortality. Multimodality treatment may improve survival for these patients. Number of cases (%) HR (CI) p-value mOS (months) vs reference Site (ref: colon) Rectum 514 (44%) 0.750 (0.648-0.867) <0.001 9 (ref: 5) Small intestine 86 (7.4%) 0.574 (0.44-0.749) <0.001 11 (ref: 5) Stage (ref: localized) Regional 201 (17%) 2.087 (1.507-2.891) <0.001 16 (ref: 38) Distant 639 (55%) 4.222 (3.110-5.733) <0.001 5 (ref: 38) Unknown/unstaged 242 (21%) 1.639 (1.160-2.315) 0.005 8 (ref: 38) Chemo (ref: none/unknown) Yes 590 (50%) 0.473 (0.404-0.553) <0.001 10 (ref:3) RT (ref: none/unknown) Yes 175 (15%) 0.733 (0.598-0.897) 0.003 12 (ref: 7) Surgery (ref: no surgery) Yes 363 (31%) 0.458 (0.385-0.546) <0.001 12 (ref: 6) Unknown 138 (12%) 0.717 (0.549-0.936) 0.01 7.5 (ref: 6)