Perineural invasion (PNI) signals poor outcomes in stage II rectal cancer and could guide chemotherapy decisions.

• 10.5% of analyzed patients showed PNI, linked to higher carcinoembryonic antigen levels and worse prognosis.
• Postoperative chemotherapy significantly improved overall and cancer-specific survival for PNI-positive patients.

Surgeons should consider PNI when assessing treatment plans, as it identifies high-risk patients who may benefit from adjuvant chemotherapy.