Impact of the number of colorectal cancer lymph node metastases on intraperitoneal lavage cytology: a multi-institutional, prospective, observational study.

PURPOSE: We previously identified T4, an undifferentiated histological type, and positive lymph node (LN) metastasis as risk factors for positive intraperitoneal lavage cytology (IPLC) in colorectal cancer (CRC) surgery. However, the number of LN metastases influencing IPLC positivity remains unknown. We conducted a multicenter, prospective, observational study to determine the threshold number of LN metastases associated with IPLC positivity and identify patients with CRC who should undergo IPLC.

METHODS

Patients with clinical stage II and III CRC who underwent tumor resection and IPLC between 2013 and 2017 were included. IPLC was performed once during laparotomy and once after tumor resection. Patients with a T4 stage, ascites, or undifferentiated types were excluded, as these factors affected IPLC. The number of LNs that influenced IPLC positivity was examined using a logistic regression analysis and the Akaike information criterion (AIC).

RESULTS

The IPLC positivity rate was 2.0%. The rate increased significantly in patients with ≥ 2 LN metastases, and stratification by five LN metastases yielded the lowest AIC value (156.9). The positivity rate was 8.9-fold higher in patients with ≥ 5 LN metastases than in those with < 5 metastases.

CONCLUSION

IPLC is recommended for patients with clinical stage III CRC and multiple LN metastases.