Hormone receptor and HER2 (human epidermal growth factor receptor 2) status are important factors to consider when dealing with breast cancer, as they can be helpful indicators of useful treatments and help differentiate between breast cancer types. When a breast tumor has hormone receptors, hormones in the body bind to these receptors, which allows the cancer cells to grow. Such hormones include estrogen and progesterone, and breast cancers can have receptors for these hormones (denoted as “positive”) or not have these receptors (denoted as “negative”).[1]

HR+ breast cancers typically grow more slowly than HR- breast cancers and have better prognosis in the short term; however, they are more likely to recur many years later. On the other hand, if HR- breast cancers recur, it is usually within the first few years after treatment. HR- breast cancers are more common in premenopausal women.[1]

Hormone receptors are usually tested for using an immunohistochemistry (IHC) test. This test involves staining breast cancer tissues removed during biopsy. At least 1% of the tumor cells tested must have hormone receptors to be considered HR+, but the exact cutoff differs between labs. Some labs may require at least 10% of the tumor cells to have hormone receptors to be considered positive. Research has shown that hormone therapy can be beneficial even for low scores and should only be ruled out if 0% of the tumor cells have hormone receptors. This test needs to be done for both estrogen and progesterone receptors. A lab result stating the hormone status is unknown is the result of one of the following: the lab test was never ordered or completed, the tumor sample was too small to get reliable results, or a very small amount of hormone receptors were found.[2] Labs may report IHC results for hormone status in the following ways.

HER2, a protein encoded by the HER2 gene, promotes growth. Therefore, breast cancers with an excess of this protein, termed HER2-positive (HER2+), tend to grow and spread more quickly than HER2-negative (HER2-) breast cancers. The HER2 status can be tested using an IHC stain or fluorescent in situ hybridization (FISH). The IHC test is usually performed first because it is less expensive and gives quicker results.3 The IHC test for HER2 status gives a score between 0 and 3.

Lab results may differ between labs, especially for the borderline cases. It is also possible for part of the breast to test HER2+ and another part to test HER2-. If the HER2 status is inconclusive from the IHC stain, the FISH test may be performed to confirm. The FISH test uses fluorescence to detect genetic material in breast cancer tissues removed during biopsy. This test gives results of the words “positive”, “negative”, or sometimes “zero”. Again, different labs have different ways of classifying results, and you may want to ask if more than one pathologist reviewed your results if it is a borderline case. The IHC test works best on fresh or frozen tissues, while the FISH test works best on wax or chemically preserved tissues.4 Breast cancers may be referred to as triple-positive if they test positive for both estrogen and progesterone receptors and have high levels of HER2.[3]