Breast tissue staining allows doctors to make specialized diagnoses of breast diseases, like breast cancer. While doctors can identify a breast mass on a mammogram, or detect the presence of cancer by looking at a biopsy specimen, breast tissue staining provides doctors insight into the biochemical causes of a breast disease. Breast tissue staining is commonly used to help diagnose breast cancer. Because breast cancers differ from patient to patient, and exhibit distinct patterns of genetic mutations, breast cancer treatments that prove effective for one patient might have no effect on another.
Estrogen Receptor Staining
A common target of breast cancer therapy is the estrogen receptor, which is a protein found on the surface of some breast cancer cells. Under normal conditions, estrogen signaling plays a role in breast cell proliferation during puberty, menstruation and pregnancy. Some cancer cells retain a sensitivity to estrogen and react to circulating estrogen by dividing. As a result, inhibiting estrogen signaling can help doctors slow or stop cancer growth, according to BreastCancer.org.
Doctors use an ER staining method to help determine whether a patient's breast cancer will respond to estrogen-targeting therapy. The doctor will remove a small piece of tissue from the tumor and use a method called immunohistochemistry, which uses molecules called antibodies to detect the presence of specific proteins, to look at the amount of ER within the tumor. If a tumor is determined to be ER-positive, meaning it contains estrogen receptors, patients often undergo estrogen-targeting therapy. If the tumor is ER-negative, and does not contain ER, doctors will perform additional testing on the tumor.
Progesterone Receptor Staining
Another common staining procedure used to characterize breast cancer is progesterone staining. Like estrogen, progesterone is a hormone naturally produced in the body that can signal to normal breast cells. Breast cancers containing the progesterone receptor, or PR, also have the ability to respond to progesterone levels in the body. As a result, patients with PR-positive breast cancers might receive hormone therapy to interrupt normal progesterone signaling, treating breast cancer growth.
Doctors use a similar biochemical technique to test for the presence of the progesterone receptor. The doctor treats a sample of breast biopsy tissue with molecules called antibodies, that can bind specifically to the progesterone receptor. The doctor then tests for antibody binding to the sample: if antibodies could bind to the tissue, then the sample contains the progesterone receptor. If they do not bind, the sample is considered PR-negative. Breast cancer patients with PR-positive breast cancers can receive hormone therapy to lower progesterone levels and treat their cancer, according to CancerHelp UK.
HER2 Staining
Another common staining procedure to characterize breast tumors is HER2 staining. Unlike ER and PR, which respond to circulating hormone levels to promote breast cancer growth, HER2 does not bind any specific factors on the surface of the cell. HER2 instead forms structures called dimers--a cluster of two protein receptors, that can then signal for cell growth. Some forms of breast cancer contain too much HER2 and the cell always receives signals to divide, driving cancer development.
Doctors routinely perform HER2 testing on breast tumors to assess the amount of HER2 found on the surface of breast cancer cells. According to Genentech, a pharmaceutical company that develops HER2-based therapies, doctors use immunohistochemistry to stain for HER2 on breast biopsy samples. Using antibodies as well as detection chemicals, the doctor scores the sample on a sale of 0 to 3. Patients with a score of 0 have little HER2, and are considered HER2-negative tumors, while patients with a higher score contain more HER2. Patients with high levels of HER2 in their breast cancer cells might respond to HER2-based therapies, such as Herceptin.
