Abstract 4380: Pre- and postoperative fecal microbiota and its association with complications after surgery in colon cancer patients

Introduction: Postoperative complications impact morbidity and mortality of colon cancer patients. Emerging evidence suggests that intestinal microbiota might play a critical role in the development of postoperative complications after gastrointestinal surgery. Here, we studied changes in fecal microbiota composition comparing samples collected before and after colon cancer surgery. Moreover, we examined whether the microbiota composition before surgery was associated with postoperative complications, and we explored potential determinants of the preoperative microbiota in colon cancer patients.

Methods: For this study, two fecal samples were provided by 78 patients with colon cancer. The first (preoperative) sample was collected shortly after diagnosis and before (median and interquartile (IQR) range of 4 (2-6) days) colon cancer surgery. The second (postoperative) sample was collected approximately 6 weeks (median and IQR of 42 (37-47) days) after surgery and before start of adjuvant chemotherapy (whenever applicable). Based on 16S ribosomal RNA gene amplicon sequencing, the fecal microbiota diversity and composition were determined. Preoperative microbiota composition of patients who developed postoperative complications in the 30 days following surgery (n=18, 23%) was compared to those who did not (n=60, 77%) using univariate and multivariate analyses. Explorative random forest analyses were conducted to identify predictors of complication status, with relative abundance of the core genera, sex, age, fecal calprotectin levels, dietary fiber intake, body mass index, smoking status, ASA classification, cancer stage and tumor location being considered as potential predictors.

Results: After surgery, microbial alpha diversity was reduced compared to the preoperative situation, whereas compositional changes over time only reached statistical significance for Lachnospiraceae NK4A136 and Coprococcus 1, which both decreased in relative abundance after surgery. Already before the start of surgery, relative abundance of the genera Bacteroides (10% vs 6%) and Lachnoclostridium (0.6% vs 0.2%) appeared to be higher in patients with complications versus those with uncomplicated recovery. In a prediction analysis, current smoking and relative abundance of Lachnoclostridium were identified as most profound predictors of complication status. Fecal calprotectin levels and current smoking status explained most (together 6%) of the overall variation in microbiota composition before surgery.

Conclusion: In this study, higher relative abundances of the genera Bacteroides and Lachnoclostridium before surgery were associated with postoperative complications in patients with colon cancer. Future studies should expand on the potential causal and pathogenic routes underlying these observations.

Citation Format: Dieuwertje E. Kok, Jannigje G. Kers, Hendriek C. Boshuizen, Niels Klaassen, Henk K. van Halteren, Flip M. Kruyt, Marjolein L. Smidt, Johannes H. De Wilt, Annemarie Boleij, Ellen Kampman, Erwin G. Zoetendal. Pre- and postoperative fecal microbiota and its association with complications after surgery in colon cancer patients. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4380.

High-dose-rate intraoperative radiotherapy for close or positive margins in patients with locally advanced or recurrent rectal cancer

PURPOSE

A high-dose-rate intraoperative radiotherapy (HDR-IORT) technique for rectum cancer was developed and the technique, local failure, and survival were analyzed.

METHODS AND MATERIALS

After the exclusion of metastatic patients, 37 patients were treated with external beam RT, surgery, and HDR-IORT between 1997 and 2000. Primary locally advanced rectum cancer was found in 18 patients and recurrent disease in 19. HDR-IORT was only administered if the resection margins were < or =2 mm. The flexible intraoperative template is a 5-mm-thick pad with 1-cm-spaced parallel catheters. Clips were placed during surgery to define the target area. A dose of 10 Gy was prescribed at a 1 cm depth from the template surface and calculated using standard plans. After treatment, the dose at the clips was calculated using the reconstructed template geometry and the actual treatment dwell times. The median follow-up of surviving patients was 3 years. No patients were lost to follow-up.

RESULTS

Overall, 12 patients (32%) had local recurrence, 5 (14%) of which were in the HDR-IORT field. The 3-year local failure rate for primary tumors and recurrent tumors was 19% and 52%, respectively (p = 0.0042). The 3-year local failure rate was 37% for negative margins and 26% for positive margins (p = 0.51). A high mean dose at the clip (17.3 Gy) was found. The overall survival was significantly different for primary vs. recurrent tumors, stage, and grade.

CONCLUSION

Because of the HDR technique, a high dose at the clips was found, with good local control. More out-of-field than in-field failures were seen. The local failure rate was significantly different for primary vs. recurrent disease.