Evaluation of the prognostic impact of intraoperative cytology results according to tumor sidedness in stage II/III resectable colorectal cancer

Aim To investigate whether colorectal cancer (CRC) sidedness is associated with intraoperative lavage cytology results, tumor recurrence, and prognosis. Method Using data from a multicenter prospective observational study conducted by the Japanese Society for Cancer of the Colon and Rectum (JSCCR), we retrospectively analyzed prognosis and recurrence patterns in pathological stage II/III right-sided and left-sided CRC, stratified by positive versus negative lavage cytology results. Results A total of 1500 patients met the inclusion criteria and were enrolled. Of these, 534 had right-sided CRC and 966 had left-sided CRC. Fifty-nine patients (3.9%) had positive lavage cytology. Among patients with recurrence, pT4, positive lavage cytology, and right-sided tumor location were independently associated with peritoneal recurrence. Among cytology-negative patients, the 5-year relapse-free survival (RFS) rate was significantly higher in right-sided than in left-sided CRC (79.6% vs. 73.4%, p = 0.01), whereas the 5-year overall survival (OS) rate did not differ significantly (89.2% vs. 87.7%, p = 0.52). Among cytology-positive patients, no statistically significant differences in RFS or OS were observed between tumor locations. However, among cytology-positive patients who developed recurrence, post-recurrence survival was significantly worse in right-sided CRC than in left-sided CRC ( p = 0.04). Conclusion Among cytology-negative patients, left-sided CRC was associated with poorer RFS than right-sided CRC, although OS did not differ. Right-sided tumor location and positive lavage cytology were independently associated with peritoneal recurrence among patients who developed recurrence. Among cytology-positive patients, right-sided CRC was associated with poorer post-recurrence survival.