Comparison of prognostic impact between positive intraoperative peritoneal and lavage cytologies in colorectal cancer

Background The prognostic value of positive intraoperative peritoneal cytology and lavage cytology, including the differences in their prognostic impact, in colorectal cancer is controversial. We aimed to investigate the prognostic values of positive peritoneal cytology and lavage cytology findings for colorectal cancer and compare their prognostic impact. Methods We retrospectively evaluated 592 clinical stage II–IV colorectal cancer patients who underwent peritoneal cytology ( n = 225) or lavage cytology ( n = 367) between November 1993 and December 2018. The prognostic factors for cancer-specific survival were identified, and the differences in cancer-specific survival were examined between the patients. Results The cytology-positive rate was 10.8% (64/592), 17.8% (40/225), and 6.5% (24/367) in the overall, peritoneal cytology, and lavage cytology groups, respectively. Both positive peritoneal cytology (hazard ratio: 2.196) and lavage cytology (hazard ratio: 2.319) were independent prognostic factors. The peritoneal cytology-positive group showed significantly poorer cancer-specific survival than the cytology-negative group (5-year: 3.5% vs. 59.5%; 10-year: 3.5% vs. 46.1%, p < 0.001). Similar results were obtained for lavage cytology (5-year: 14.1% vs. 73.9%; 10-year: 4.7% vs. 63.5%, p < 0.001). The cancer-specific survival was not significantly different between the peritoneal cytology-positive and lavage cytology-positive groups ( p = 0.058). Both positive peritoneal and lavage cytology were associated with poorer cancer-specific survival across all colorectal cancer stages. Conclusions Positive peritoneal and lavage cytology are associated with worse cancer-specific survival in colorectal cancer. The prognostic impact was comparable between positive lavage and peritoneal cytology. Thus, cytology should be a standard assessment modality for colorectal cancer.