The progesterone receptor (PR) is a special type of protein found inside certain cells in the body. It belongs to a group of proteins called nuclear hormone receptors, which control how cells respond to hormones. Progesterone receptors specifically respond to the hormone progesterone, which plays a vital role in reproductive health, menstrual cycles, pregnancy, and overall hormone balance. Normally, progesterone receptors are located in the cell’s nucleus, where they control cell activities by switching specific genes on or off.
Progesterone receptors are usually found in tissues that respond directly to progesterone, such as:
Uterus (endometrium)
Breast tissue
Ovaries
Brain
In these areas, progesterone is essential for regulating menstruation, fertility, pregnancy, and other aspects of reproductive health.
Pathologists test for progesterone receptors using a method called immunohistochemistry (IHC). During this test, specialized antibodies designed to detect progesterone receptors are applied to a tissue sample. If the progesterone receptors are present, these antibodies attach to them, causing a visible color change when viewed under the microscope.
Pathologists examine the sample carefully, looking specifically at the cell’s nucleus to see if staining occurs.
Test results are described as:
Positive: Progesterone receptors are present in the cells.
Negative: Progesterone receptors are absent.
Pathologists also typically report:
The percentage of cells containing progesterone receptors.
The intensity (strength) of the staining.
For example, a report might state: “70% of tumour cells are PR-positive, with moderate staining intensity.”
This information helps doctors predict the tumour’s behavior and choose the best treatment options.
Both benign (non-cancerous) and malignant (cancerous) tumours can contain progesterone receptors. This is especially true if the tumour started from tissues that normally respond to progesterone.
Examples of tumours that often express progesterone receptors include:
Benign tumours:
Breast fibroadenomas.
Malignant tumours:
Certain types of breast cancer (PR-positive breast cancer).
Uterine (endometrial) cancer.
Ovarian cancers.
Breast cancers that express progesterone receptors often depend on progesterone for their growth. Identifying PR-positive cancers is important because they typically grow more slowly and often have a better outlook (prognosis). They also frequently respond well to hormone-blocking treatments that reduce progesterone’s effects on cancer cells.
Testing tumour tissue for progesterone receptors provides doctors and pathologists with valuable information to:
Predict how quickly the tumour might grow.
Determine the overall prognosis or expected outcome.
Choose the most effective treatments, such as hormone-blocking therapies, which specifically target PR-positive cancers.
If your pathology report mentions progesterone receptor status, you may wish to ask your doctor:
Are progesterone receptors present (positive) or absent (negative) in my tumour?
How does progesterone receptor status affect my prognosis or treatment?
What treatment options are recommended based on my PR test results?
Do I need further testing or monitoring related to hormone receptor status?
Understanding the role of the progesterone receptor can help you become more involved in your care and support informed discussions about your diagnosis and treatment plan.