Perineural invasion (PNI) is widely studied in malignant
tumors, and its prognostic significance is well demonstrated in the head and neck and prostate
carcinomas, but its significance in
rectal cancer is controversial. Most studies have focused on evaluating mural PNI (
mPNI); however, extramural PNI (ePNI) may influence the prognosis after
rectal cancer resection. We evaluated the prognostic value of ePNI compared with
mPNI and with non-PNI, in rectal resections after preoperative
chemoradiotherapy in 148 patients with pT3 and pT4 rectal
carcinomas. PNI was identified in 35 patients (23.6%), 60% of which were in the
mPNI group. Factors associated with PNI were
tumor invasion depth,
lymph node metastasis, lymphovascular invasion, and venous invasion; patients with PNI were more likely to have positive
resection margins (65.7% versus 11.6%). ePNI, compared with
mPNI, was associated with female sex (64.3% versus 28.6%),
positive surgical margins (42.8% versus 28.6%), recurrence (50% versus 28.6%), and death (92.9% versus 28.6%). The 5-year disease-specific survival rate was 78.1% for patients without PNI, compared with 63.7% for the
mPNI group and 26.4% for the ePNI group (P<.001). On multivariate analysis, the independent adverse prognostic factors were ePNI (odds ratio [OR], 22.17; 95% confidence interval [CI], 17.03-24.58; P<.001), overall recurrence (OR, 9.19; CI, 6.11-10.63; P=.002), clinical stage IV (OR, 8.56; CI, 6.34-9.47; P=.003), and
positive surgical margin (OR, 3.95; CI, 2.00-4.28; P=.047). In conclusion, we demonstrated the prognostic effect of ePNI for disease-specific survival in surgically resected pT3-pT4
rectal cancer patients with preoperative
chemoradiotherapy.