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Purpose:Small-bowel adenocarcinoma (SBA) is rare, and no standard of care exists for metastatic disease beyond first-line FOLFOX/CAPOX. SBA has higher rates of microsatellite instability (MSI-H) and T-lymphocyte infiltration than other gastrointestinal cancers. We hypothesize that pembrolizumab, a PD-1 inhibitor, will induce antitumor response.Patients and Methods:Patients with previously treated advanced SBA received pembrolizumab 200 mg i.v. every 3 weeks until disease progression (PD), toxicity, or 35 doses maximum. Primary endpoint was confirmed overall response rate (ORR) with secondary progression-free survival (PFS), overall survival (OS), and toxicity assessment endpoints. Outcomes were stratified by tumor location, microsatellite stability (MSS) or instability (MSI-H), and PD-L1 level.Results:Forty patients were treated for a median duration of four cycles (range, 1–35). All patients are off study treatment due to PD (75%), death (10%), 35 cycles completed (8%), refusal (3%), and adverse effects (AEs, 5%). Three confirmed partial responses [PRs; 8%; 95% confidence interval (CI), 2–20] did not meet predefined success criteria of ORR 30%. Median OS (7.1 months; 95% CI, 5.1–17.1) and median PFS (2.8 months; 95% CI, 2.7–4.2) were similar across primary tumor sites. One confirmed PR (3%) was seen in patients with low MSS/MSI tumors and correlated with high tumor mutation burden (TMB). Fifty percent of patients with MSI-H tumors achieved PR and remain alive without progression. Twenty-five patients (63%) had grade ≥3 AEs and 11 patients (28%) had grade 4/5 AEs.Conclusions:In the largest study of SBA to date, pembrolizumab did not induce the hypothesized response rate; however, we did identify responses in key biomarker-selected cohorts.

Purpose: Small-bowel adenocarcinoma (SBA) is rare, and no standard of care exists for metastatic disease beyond first-line FOLFOX/CAPOX. SBA has higher rates of microsatellite instability (MSI-H) and T-lymphocyte infiltration than other gastrointestinal cancers. We hypothesize that pembrolizumab, a PD-1 inhibitor, will induce antitumor response. Patients and Methods: Patients with previously treated advanced SBA received pembrolizumab 200 mg i.v. every 3 weeks until disease progression (PD), toxicity, or 35 doses maximum. Primary endpoint was confirmed overall response rate (ORR) with secondary progression-free survival (PFS), overall survival (OS), and toxicity assessment endpoints. Outcomes were stratified by tumor location, microsatellite stability (MSS) or instability (MSI-H), and PD-L1 level. Results: Forty patients were treated for a median duration of four cycles (range, 1–35). All patients are off study treatment due to PD (75%), death (10%), 35 cycles completed (8%), refusal (3%), and adverse effects (AEs, 5%). Three confirmed partial responses [PRs; 8%; 95% confidence interval (CI), 2–20] did not meet predefined success criteria of ORR 30%. Median OS (7.1 months; 95% CI, 5.1–17.1) and median PFS (2.8 months; 95% CI, 2.7–4.2) were similar across primary tumor sites. One confirmed PR (3%) was seen in patients with low MSS/MSI tumors and correlated with high tumor mutation burden (TMB). Fifty percent of patients with MSI-H tumors achieved PR and remain alive without progression. Twenty-five patients (63%) had grade ≥3 AEs and 11 patients (28%) had grade 4/5 AEs. Conclusions: In the largest study of SBA to date, pembrolizumab did not induce the hypothesized response rate; however, we did identify responses in key biomarker-selected cohorts.

Background: Small bowel adenocarcinoma (SBA) is rare, and no standard of care exists for metastatic SBA beyond first-line FOLFOX/CAPOX. Later-line therapy has been extrapolated from colorectal cancer (CRC) studies, though SBA is biologically distinct with higher rates microsatellite instability (MSI-H) and intratumoral T-lymphocyte infiltration. We hypothesize that pembrolizumab, a PD-1 inhibitor, will induce antitumor response. Methods: Previously treated advanced SBA patients received pembrolizumab 200 mg IV q3 weeks until disease progression (PD), toxicity, or to 35 dose maximum. Primary endpoint was confirmed overall response rate (ORR) with secondary survival and safety endpoints. Outcomes were stratified by tumor location, microsatellite stability (MSS) or instability (MSI-H), and PD-L1 level. Findings: 40 patients were treated for median duration of 4 cycles (range 1-35). MSI status was available for 36 patients (90%). All 40 patients are off study treatment due to: PD (75%), death (10%), 35 cycles completed (8%), refusal (3%), and adverse effects (AE, 5%). Three confirmed partial responses (PR) (8%; 95% CI: 2-20) did not meet pre-defined success criteria. Median overall survival (OS) 7 . 1 mo (95% CI: 5 . 1-17 . 1) and median progression free survival (PFS) 2 . 8 mo (95% CI: 2 . 7-4 . 2) were similar across primary tumor sites. One confirmed PR was seen in 32 MSS/MSI-low patients (3%). MSS response correlated with high tumor mutation burden (TMB). Two of four MSI-H patients had a confirmed PR (50%) and remain alive without progression. 25 patients (63%) had grade ≥ 3 AEs, 11 pts (28%) had grade 4/5 AEs. Interpretation: In the largest study of SBA to date, and the first using immunotherapy, pembrolizumab did not achieve the hypothesized response rate; however, we did identify responses in certain biomarker-selected cohorts. Trial Registration: RU021502I (ACCRU), MISP #52192 (Merck), NCT02949219 (clinicaltrials.gov). Funding Statement: Primary study funding and investigational product was provided by the Merck Investigator Studies Program (MISP), and additional site-specific funding provided by the Kavanagh Family Foundation (MDACC) and Kevin T. Doner Memorial Fund (MDACC). Declaration of Interests: None to declare Ethics Approval Statement: Ethics board review and human research protections monitoring were performed at each institution. The trial was conducted according to ICH GCP.

Previous studies have emphasized the role of bile acid and fat malabsorption as the cause of the diarrhea that may follow ileal and right colon resection; unabsorbed bile acids and fat are believed to reduce sodium chloride and water absorption in the remaining colon. In this paper we report studies in eight patients with severe postresection diarrhea, in search of a more basic defect in sodium chloride absorption, ie, a loss of sodium chloride absorptive capacity as a direct consequence of resection of sodium chloride absorption sites. First, we determined whether or not diarrhea persisted during a 48-hr fast; in all patients diarrhea and large fecal electrolyte losses continued during a fast. Second, we measured sodium chloride and water absorption rates during total gut perfusion with a balanced electrolyte solution; compared to normal controls, the patients absorbed 23–31% less water, sodium, and chloride. In three patients who could be studied further, the absorptive defect was markedly accentuated when the perfusing solution was such that sodium chloride absorption had to take place against a concentration gradient. These observations indicate that postresection diarrhea patients have a reduced capacity to absorb sodium chloride, particularly when there is a concentration gradient between lumen and plasma. Although all of these patients had malabsorption of radiolabeled taurocholic acid, there was only a modest and statistically insignificant reduction in daily stool weight during treatment with large doses of cholestyramine, suggesting that bile acid malabsorption was not responsible for a major part of their diarrhea. We postulate that a loss of ileal and colonic absorptive capacity for sodium chloride rather than a cathartic effect of unabsorbed bile acids or fat is the major cause of diarrhea in these patients.