Interim analysis results of gut microbiota in patients with unresectable cholangiopancreatic cancer: SCRUM-Japan MONSTAR-SCREEN.

733 Background: MONSTAR-SCREEN prospectively assessed the gut microbiota of 2000 patients (pts) with advanced solid cancer at 31 Japanese institutions. Here, we report the interim analysis results of the correlation between gut microbiota and the efficacy of first-line chemotherapy in pts with unresectable pancreatic cancer (PC) and bile tract cancer (BTC). Methods: We analyzed unresectable 205 PC and 83 BTC pts with clinical data as data cut-off on April 30, 2021, and 16S ribosome analysis results of stool samples. Among PC pts, 133 and 40 were treated with GnP (gemcitabine (GEM) plus nab-paclitaxel) and FOLFIRINOX (5-fluorouracil, leucovorin, irinotecan, and oxaliplatin), respectively. Among BTC pts, 32 and 33 were treated with GC (GEM plus cisplatin) and GCS (GEM, cisplatin, plus S-1), respectively. Pts with an above-median overall survival (OS) were defined as long-term survivors (LTS), and those with below-median OS and OS events were defined as short-term survivors (STS). We compared the alpha diversity index (ADI) of LTS and STS, and identified potential microbial biomarkers of LTS, STS, responders, and non-responders to first-line chemotherapy according to RECIST version 1.1, by linear discriminant analysis effect size (LEfSe). In each cohort, the top three microbiota with linear discriminant analysis scores of ≥ 3.0 were considered significant. Results: The median OS of PC and BTC pts was 13.5 and 15.9 months, respectively. In PC pts, no significant difference was noted in the ADI between LTS (n=20) and STS (n=40). In BTC pts, the ADI of LTS (n=10) was significantly higher than that of STS (n=20) in the Shannon index. LEfSe analysis in PC pts revealed that Burkholderiales and Sutterellaceae were predominant in LTS, while Lactobacillaceae was, in STS. In PC pts, Brachyspiraceae and Erysipelotrichales were predominant in responders (n=67), while Enterococcaceae and Lactobacillaceae were, in non-responders (n=137). In BTC pts, Peptostreptococcaceae, Fusobacteriaceae, and Clostridiaceae in LTS; Cardiobacteriaceae, Prevotellaceae, and Actinobacteriota in responders (n=24); and Bacilli in non-responders (n=59) were overrepresented. Conclusions: This interim analysis identified potential biomarkers of the gut microbiota that may contribute to the prognosis and efficacy of chemotherapy in pts with unresectable PC and BTC. The results of this analysis will be validated in the primary analysis.