Reactive changes

by Jason Wasserman MD PhD FRCPC
June 16, 2022


What are reactive changes?

The term ‘reactive changes’ is used in pathology reports to describe cells that look abnormal under a microscope as a result of alterations in their environment. Common alterations include infection, physical injury, medication effects, and inflammation. Reactive changes can be seen anywhere in the body. Reactive changes are non-cancerous or benign.

reactive changes

This picture shows reactive changes caused by a type of injury called an ulcer.

What causes reactive changes?

Anything that changes the environment of a tissue can cause the cells in the tissue to show reactive changes. For example, common causes include inflammation, viral or bacterial infections, medications/drugs, physical trauma/stress on a tissue, and radiation. Reactive changes can also be seen in the non-cancerous cells surrounding a benign (non-cancerous) or malignant (cancerous) tumour.

What does it mean if my pathology report says ‘favour’ reactive?

Pathologists use the term ‘favour’ when the features seen under a microscope are most likely reactive but when other types of changes cannot be completely excluded. For example, sometimes it can be difficult for a pathologist to tell the difference between reactive changes and a type of abnormal growth called ‘dysplasia’. This is because both of these two conditions share many microscopic features. In this situation ‘favour’ would be used to show that there was some uncertainty with the diagnosis and that further diagnostic tests may be necessary.

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