HER2 Testing in Breast Cancer

HER2 (Human epidermal growth factor receptor 2) is a protein found on the breast cancer cells. It is sometimes called ‘tumour marker’. It controls cancer growth and spread. Individuals diagnosed with breast cancer are asked to test themselves for HER2 to detect the presence of this in the body. Some have this, some don’t. The treatment of the type of breast cancer the individual has been diagnosed for, depends on the results of HER2 as well.

In HER2 positive individuals, breast cancer will be more aggressive and might spread more quickly than in others. If the person is HER2 positive, the doctor can determine how well he or she responds to treatment. The appropriate treatment methods can be chosen, providing the patient with a better chance of survival. Presence of HER2 also suggests that there is a higher risk of recurrence — around 5 times the recurrence risk as that faced by HER2 negative cases. However, they have a 77.1% chance of a 5-year survival without recurrence. So, it is important to check if a patient is HER2 positive or not.

How is the HER2 protein linked to breast cancer?

HER2 protein is generated by HER2 genes in the body. HER2 influences how breast cells grow, divide or repair themselves. Sometimes, the HER2 gene multiplies uncontrollably in a process known as HER2 gene amplification. This leads to an overproduction of HER2 proteins. This, in turn, leads to an uncontrolled multiplication and growth of breast cells. This situation is diagnosed as HER2 positive breast cancer. Therefore, such cancers are aggressive and can come back more than HER2 negative breast cancers.

Tests for HER2 detection

There are four tests to detect a patient’s HER2 status. They are:

  1. ImmunoHistoChemistry Test (IHC test): This test checks if there is too much HER2 protein in the cancer cells. The test results would be stated as 0 (negative), 1+ (negative), 2+ (borderline), 3+ (positive). If the result is 2+ (borderline) and you require a further assessment, you can get your sample retested with any one of the following tests too.
  2. Fluorescence In Situ hybridisation Test (FISH Test): FISH test finds out if there is HER2 gene amplification or not. The result would be stated as positive (HER2 gene amplification) or negative (no HER2 gene amplification).
  3. Subtraction Probe Technology Chromogenic In Situ Hybridisation (SPoT Light HER2 CISH Test): This test, like FISH test, also aims to find if there are too many copies of the HER2 gene in the cancer cells.
  4. Inform Dual In Situ Hybridisation (Inform HER2 Dual ISH Test): This test, like the FISH and SpoT Light tests, detects if there is HER2 gene amplification or not (positive or negative, respectively).

If your test result is IHC 3+, or FISH positive, or SPoT Light HER2 CISH positive or Inform HER2 Dual ISH positive, then you can discuss with your doctor about HER2 oriented treatment plans.

Some breast cancers which test HER2 positive can turn negative in due course, and vice versa. If the cancer recurs in future, HER2 testing should be carried out again to determine the current status.

Discussing your HER2 results with your doctor

HER2 test results may vary between labs. This is because different labs have different criteria of assessment. This happens mostly when the results are in the borderline area when they are not strongly positive or strongly negative. It could also happen that sample from one part of the cancer might test positive and sample from another part might test negative. It would be advisable to discuss your HER2 results with your doctor to assess how they can be interpreted for possible treatment options.