In pathology, perineural invasion, abbreviated PNI, refers to the invasion of cancer to the space surrounding a nerve. it's common in head and neck cancer, prostatic adenocarcinoma and colorectal cancer. Perineural invasion is a vital mechanism for local spread in certain malignant cutaneous neoplasms and is related to aggressive tumor growth. Perineural invasion was defined as tumor cells touching or invading a nerve. The diameter of nerves with PNI was measured with an optical micrometer. glandular cancer incorporates a propensity to invade and grow along nerves, a phenomenon called perineural invasion (PNI). Perineural spread of tumor may be a style of local invasion within which primary tumors cells spread along the tissues of the nerve sheath. Perineural Invasion (PNI) of tumor cells was first discovered by Cruveilhier in 1835, when he reported mammary carcinoma invading the facial. Perineural tumour spread (PNTS) in head and neck oncology is most frequently caused by epithelial cell carcinoma. Perineural invasion (PNI) is an adverse prognostic consider patients with mouth epithelial cell carcinoma (OCSCC). Perineural spread (PNS) refers to tumor growth along large nerves, a macroscopic analog of microscopic perineural invasion.