When reading p53 immunohistochemistry, a wild-type pattern shows scattered nuclei of varying intensity. Two aberrant patterns signal a TP53 mutation: strong, diffuse nuclear overexpression, and complete absence of staining in the lesional cells (the null pattern). The null pattern is easily mistaken for a negative, normal result. Always check that the internal control, such as stromal or inflammatory cells, has stained before calling a null pattern.
- Look for scattered, variable nuclear staining as the wild-type pattern.
- Report strong diffuse overexpression as aberrant.
- Report complete loss in lesional cells with a positive internal control as aberrant (null pattern).
- Call the result equivocal or repeat the stain if the internal control has not stained.
Why it matters
Misreading a null pattern as normal can downgrade dysplasia or a high-grade carcinoma.
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