The androgen receptor (AR) is a protein found in certain cells that acts as a receptor for hormones called androgens — a group that includes testosterone. When an androgen enters a cell and binds to the androgen receptor, it sends a signal to the cell’s nucleus telling it to grow and divide. In healthy tissue, this is a normal, regulated process. In some cancers, however, the androgen receptor plays a key role in driving tumour growth — meaning that blocking androgens or the androgen receptor itself is a core part of treatment. Testing for AR in a tumour helps pathologists identify the type of cancer and tells your medical team whether hormone-blocking therapies may be effective.
Why do pathologists test for the androgen receptor?
AR testing is performed for two main purposes:
- To help identify the type of tumour. Strong AR positivity is a characteristic feature of certain cancers — particularly salivary duct carcinoma and apocrine-type breast cancers — and forms part of the diagnostic criteria for these tumour types.
- To guide treatment decisions. Tumors that express AR may respond to therapies that block androgen signals. This is most established in prostate cancer, where lowering testosterone or blocking the androgen receptor is a cornerstone of treatment. It is also relevant in a subset of breast cancers and salivary gland cancers.
How is AR tested?
Pathologists test for AR using a laboratory technique called immunohistochemistry (IHC). A special antibody designed to bind only to the androgen receptor protein is applied to a thin slice of tumour tissue. Where the protein is present, the antibody triggers a color change visible under the microscope. The color appears in the nucleus — the control center of the cell — because that is where the androgen receptor is normally found. The result is described as positive or negative, and often includes an estimate of the percentage of tumour cells stained and the degree of staining.
Which cancers are commonly tested for AR?
AR testing is most important in:
- Prostate cancer — the androgen receptor is central to prostate cancer biology. Normal prostate cells rely on androgens to function, and most prostate cancers remain dependent on androgen signaling to grow. This is why androgen deprivation therapy — treatment that lowers testosterone levels or blocks the androgen receptor — is a primary treatment for advanced prostate cancer. AR testing is also used to detect specific changes in the receptor (such as AR-V7) that can cause resistance to certain hormone-blocking drugs. For more information, see the guide to diagnosing prostatic adenocarcinoma.
- Breast cancer — AR is expressed in a range of breast cancer subtypes. It is particularly characteristic of invasive apocrine carcinoma of the breast, a subtype that is typically negative for estrogen and progesterone receptors but strongly positive for AR. In these cancers, AR-targeted treatments are an area of active research and may be used in some cases. AR positivity is also seen in some triple-negative breast cancers, where it defines a subgroup that may benefit from anti-androgen therapies.
- Salivary duct carcinoma — AR is positive in the large majority of salivary duct carcinomas, an aggressive type of salivary gland cancer. Because salivary duct carcinoma has a microscopic appearance similar to apocrine cells, AR positivity is both a diagnostic marker and a potential treatment target. Anti-androgen therapy is used in advanced AR-positive salivary duct carcinoma.
- Other apocrine tumors — Apocrine cells throughout the body normally produce AR, and tumors derived from these cells — including certain skin tumors and intraductal carcinoma of the salivary glands — are typically AR-positive.
How results are reported
AR results are reported as either positive or negative:
- Positive (reactive) — the androgen receptor protein was detected in the tumour cells. The result may also include the percentage of positive cells (e.g., “90% AR-positive”) and the staining intensity (weak, moderate, or strong). A higher percentage and stronger intensity generally indicate a greater level of androgen receptor activity in the tumour.
- Negative (non-reactive) — the androgen receptor protein was not detected. This suggests the tumour is unlikely to respond to anti-androgen treatments, and other treatment pathways will be considered.
Questions to ask your doctor
- Was my tumour tested for the androgen receptor, and what did the result show?
- Does my AR result affect which treatments are available to me?
- If my tumour is AR-positive, is hormone-blocking therapy part of my treatment plan?
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