PR-
Meaning of PR-: The absence matters mainly in combination, since what it adds depends entirely on whether the estrogen receptor is present too.
Definition of PR-
PR- means that testing found no meaningful progesterone receptor in a tissue sample. In a breast cancer that is also estrogen receptor positive, the absence of this second receptor suggests the estrogen pathway is not working in the usual way, and such tumors tend to behave more aggressively than those positive for both.
How is a PR- result read next to ER?
| Combination | What it indicates |
|---|---|
| ER positive, PR negative | Endocrine treatment is still used, but benefit is less consistent and the outlook somewhat worse |
| ER negative, PR negative, HER2 positive | Treatment is directed at HER2 rather than at hormones |
| ER negative, PR negative, HER2 negative | Triple negative disease, treated with chemotherapy and in some cases immunotherapy |
A negative result therefore carries almost no meaning in isolation. Beside an estrogen receptor positive result it is a modest warning; beside a negative one it forms part of a different disease category altogether.
Why does the combination matter more than either alone?
Because the progesterone receptor is produced in response to estrogen signaling, its absence in a tumor that carries the estrogen receptor implies the pathway is disrupted somewhere downstream. Such tumors are more often higher grade and more often driven partly by other growth pathways, which is the working explanation for their less predictable response to endocrine treatment. The disruption does not remove the option: the estrogen receptor is still present and still a target, so treatment continues to be based on it. What changes is the confidence attached to the prediction, and conveying that is exactly what a hormone receptor profile exists to do.
How reliable is a negative result?
Reasonably, but not absolutely. The result depends on how the tissue was fixed, how long it waited before processing, which antibody was used and how the stain was scored, which is why laboratories run controls and follow standardized procedures. Receptor status can also change: a recurrence or a distant deposit may test differently from the original tumor, so a new sample is often taken rather than relying on the earlier report. What is being described is a progesterone receptor negative finding on testing of that tissue, not the absence of the hormone progesterone from the body.
Also known as
Used in a sentence
The biopsy results showed a PR- tumor with a separately reported estrogen receptor status.
Good to know
PR- status refers to the absence of the receptor on testing rather than the absence of the hormone progesterone itself, and it is assessed separately from estrogen receptor status.