Background Selected patients with colorectal peritoneal metastases are treated with cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). The concentration of intraperitoneal chemotherapy reflects the administered dose and perfusate volume. The aim of this study was to calculate intraperitoneal chemotherapy concentration during HIPEC and see whether this was related to clinical outcomes. Methods An observational multicentre study included consecutive patients with colorectal peritoneal metastases who were treated with CRS–HIPEC between 2010 and 2018 at three Dutch centres. Data were retrieved from prospectively developed databases. Chemotherapy dose and total circulating volumes of carrier solution were used to calculate chemotherapy concentrations. Postoperative complications, disease‐free and overall survival were correlated with intraoperative chemotherapy concentrations. Univariable and multivariable logistic regression, Cox regression and survival analyses were performed. Results Of 320 patients, 220 received intraperitoneal mitomycin C (MMC) and 100 received oxaliplatin. Median perfusate volume for HIPEC was 5·0 (range 0·7–10·0) litres. Median intraperitoneal chemotherapy concentration was 13·3 (range 7·0–76·0) mg/l for MMC and 156·0 (91·9–377·6) mg/l in patients treated with oxaliplatin. Grade III or higher complications occurred in 75 patients (23·4 per cent). Median overall survival was 36·9 (i.q.r. 19·5–62·9) months. Intraperitoneal chemotherapy concentrations were not associated with postoperative complications or survival. Conclusion CRS–HIPEC was performed with a wide variation in intraperitoneal chemotherapy concentrations that were not associated with complications or survival.

Background Cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) is a potentially curative treatment for patients with colorectal peritoneal metastases (CRPM). Patient selection is key to optimizing outcomes after CRS/HIPEC. The aim of this study was to determine the prognostic value of ascites diagnosed on preoperative imaging. Methods A prospective database of patients eligible for CRS/HIPEC between 2010 and 2020 was retrospectively analyzed. The presence of ascites, postoperative complications, overall survival (OS), disease-free survival (DFS), and completeness of cytoreduction were assessed. Univariable and multivariable logistic regression was performed to identify independent predictors for outcome. Results Of the 235 included patients, 177 (75%) underwent CRS/HIPEC while 58 (25%) were not eligible for CRS/HIPEC. In 42 of the 177 patients (24%) who underwent CRS/HIPEC, ascites was present on preoperative computed tomography (CT) imaging. Peritoneal Cancer Index (PCI) score was significantly higher in patients with preoperative ascites compared with patients without (11 [range 2–30] vs. 9 [range 0–28], respectively; p = 0.011) and complete cytoreduction was more often achieved in patients without ascites (96.3% vs. 85.7%; p = 0.007). There was no significant difference in median DFS and OS after CRS/HIPEC between patients with and without ascites {10 months (95% confidence interval [CI] 7.1–12.9) vs. 9 months (95% CI 7.2–10.8), and 25 months (95% 9.4–40.6) vs. 27 months (95% CI 22.4–31.6), respectively}. Conclusions Ascites on preoperative imaging was not associated with worse survival in CRS/HIPEC patients with CRPM. Therefore, excluding patients from CRS/HIPEC based merely on the presence of ascites is not advisable.

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