Prognostic evaluation of perineural invasion in rectal cancer.

To evaluate whether perineural invasion (PNI) is an important prognostic factor in patients with rectal cancer, we reviewed the records of 373 patients who underwent curative surgery. Thirty-seven patients (9.9%) were identified as having tumors with PNI. The incidence of PNI was significantly increased in lesions categorized as stage III by the International Union Against Cancer (UICC) system (20%). There was a significant difference in local recurrence between patients with stage III lesions with PNI and those with stage III lesions without PNI (p < 0.005). Also, patients with PNI of stage III lesions had a significantly lower 8-year survival rate (26.7%, p < 0.001). We conclude that PNI is an important factor influencing the prognosis of patients with stage III disease. PNI should be classified as a subgroup of the clinical stage.