Perineural invasion (PNI)

November 8, 2023

perineural invasion

Perineural invasion (PNI) is used to describe tumour cells in the space around a nerve. It is usually only seen in malignant (cancerous) tumours and used by pathologists as evidence that a tumour is malignant. PNI is important because the tumour cells can use the nerve to spread into surrounding tissues. This increases the risk that the tumour will re-grow after treatment. Intraneural invasion is a related term that means tumour cells inside of a nerve.

PNI can only be identified when tissue is examined under the microscope by a pathologist and it is considered a classic microscopic feature of cancer because it is rarely seen in benign (noncancerous) tumours. For many types of cancer, PNI is considered a poor prognostic factor because tumours that show PNI are more likely to spread into surrounding tissues or re-grow even after being surgically removed. For some types of cancers such as adenocarcinoma of the prostate gland, PNI is also used to determine the pathologic tumour stage with tumours that show PNI being given a higher tumour stage.

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This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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