Peritoneal lavage cytology in patients with curative resection for stage II and III colorectal cancer: A multi-institutional prospective study

Aim: To clarify the usefulness of intraoperative lavage cytology in patients undergoing curative resection for pStage II-III colorectal cancer in a prospective multicenter study. Methods: Patients preoperatively diagnosed with stage II-III colorectal cancer between 2013 and 2017 from 20 hospitals were enrolled. Lavage cytology was performed twice during the surgery. The primary endpoint was the effect of lavage cytology on the 5-year relapse-free survival (RFS) in patients with pStage II-III colorectal cancer. The secondary endpoint was the effect of lavage cytology on the 5-year overall survival (OS) and peritoneal recurrence. Results: A total of 1378 patients were eligible for analysis. The number of patients with pStage II-III colorectal cancer was 670 and 708, respectively. Fifty-four patients (3.9%) had positive cytological results. In pStage II patients, the 5-year RFS rates with positive and negative cytology were 61.1% and 81.6%, respectively (p = 0.023). The 5-year OS rates were 67.1% and 91.7%, respectively (p = 0.0083). However, there was no difference in RFS or OS between pStage III patients with positive and negative cytology results. The peritoneal recurrence rates were 11.8% and 1.5% in pStage II patients with positive and negative cytology results, respectively (p = 0.032). These rates were 10.5% and 2.5% in patients with stage III disease, respectively (p = 0.022). Conclusion: Stage II colorectal cancer patients with negative cytology had better outcomes than those with positive cytology. Peritoneal lavage cytology is useful for predicting peritoneal recurrence after curative resection of stage II-III colorectal cancer.