Perineural invasion is an independent predictor of outcome in colorectal cancer.

PURPOSE: Perineural invasion (PNI) is associated with decreased survival in several malignancies, but its significance in colorectal cancer (CRC) remains to be clearly defined. We evaluated PNI as a potential prognostic indicator in CRC, focusing on its significance in node-negative patients.

PATIENTS AND METHODS: We identified 269 consecutive patients who had CRC resected at our institution. Tumors were re-reviewed for PNI by a pathologist blinded to the patients' outcomes. Overall and disease-free survivals were determined using the Kaplan-Meier method, with differences determined by multivariate analysis using the Cox multiple hazards model. Results were compared using the log-rank test.

RESULTS: PNI was identified in less than 0.5% of the initial pathology reports. On rereview, 22% of tumors in our series were found to be PNI positive. The 5-year disease-free survival rate was four-fold greater for patients with PNI-negative tumors versus those with PNI-positive tumors (65% v 16%, respectively; P < .0001). The 5-year overall survival rate was 72% for PNI-negative tumors versus 25% for PNI-positive tumors. On multivariate analysis, PNI was an independent prognostic factor for both cancer-specific overall and disease-free survival. In a subset analysis comparing patients with node-negative disease with patients with stage III disease, the 5-year disease-free survival rate was 56% for stage III patients versus 29% for patients with node-negative, PNI-positive tumors (P = .0002). Similar results were seen for overall survival.

CONCLUSION: PNI is grossly underreported in CRC and could serve as an independent prognostic factor of outcomes in these patients. PNI should be considered when stratifying CRC patients for adjuvant treatment.