Clinical significance of perineural invasion in stages II and III colorectal cancer

Purpose: This study aimed to determine the prognostic value of perineural invasion (PNI) in patients with colorectal cancer (CRC), particularly patients with TNM stage II and stage III. Methods: A total of 159 CRC patients who had undergone radical resection were retrospectively analyzed. Histopathological evaluation oftissue samples was conducted on hematoxylin and eosin-stained sections. PNI was considered positive when cancer cells were observed inside the nerve sheath, or when at least 33% of the nerve periphery was surrounded by cancer cells. A 3-tier grading system (PNIO, PNII, PNI2) based on the depth of PNI was used to assess the localization of PNI in the bowel. PNI and other prognostic factors were evaluated by survival analysis. Results: PNI status in CRC significantly affected postoperative overall survival (P< 0.001). The five-year survival rates for PNI-negative and PNI-positive patients were 77% and 32%, respectively. PNI was closely correlated with tumor gross type, tumor grade, depth of invasion, lymph node metastasis, clinical stage, vessel invasion, tumor budding grade, and tumor growth pattern. Multivariate analysis revealed that PNI was an independent prognostic factor (HR = 2.223, P= 0.003). The survival of PNI-positive patients was significantly poorer than that of PNI-negative patients in stages II and III (P= 0.003 and P= 0.008, respectively). The overall survival of colorectal patients was in the descending order of PNI-negative at stage II, PNI-positive at stage II/PNI-negative at stage III, and PNI-positive at stage III (P< 0.001). When the PNI status and T stage were considered together, overall survival curves of the PNI2 patients were significantly worse than those of PNII patients in pT4 stage (P= 0.019). Conclusions: PNI isa poor independent prognostic factor for CRC. It could complement classic TNM staging classification in stratifying CRC patients in stages II and III. Assessment of the site-specific distribution of PNI may further enhance the impact of PNI contribution to the prognosis of CRC. 2015 Elsevier GmbH. All rights reserved.