A friend of mine has HER2-positive breast cancer. Can you tell me what this means?

Answers from Timothy J. Moynihan, M.D.

HER2-positive breast cancer is a breast cancer that tests positive for a protein called human epidermal growth factor receptor 2 (HER2), which promotes the growth of cancer cells.

In about 1 of every 5 breast cancers, the cancer cells have a gene mutation that makes an excess of the HER2 protein. HER2-positive breast cancers tend to be more aggressive than other types of breast cancer. They're less likely to be sensitive to hormone therapy, though many people with HER2-positive breast cancer can still benefit from hormone therapy.

Treatments that specifically target HER2 are very effective. These treatments are so effective that the prognosis for HER2-positive breast cancer is actually quite good.

Treatments include:

  • Trastuzumab (Herceptin)
  • Lapatinib (Tykerb)
  • Pertuzumab (Perjeta)
  • Ado-trastuzumab emtansine (Kadcyla)

In addition, there are several new medications being developed that also target HER2 and are being tested in clinical trials.

Certain standard chemotherapy drugs also can be effective in treating HER2-positive breast cancers, although these drugs don't specifically target the HER2 protein.

Experts recommend that every invasive breast cancer be tested for the presence of HER2 because the results significantly impact treatment recommendations and decisions. HER2 testing is not done routinely for ductal carcinoma in situ, except as part of a clinical trial.

Whenever breast cancer recurs or spreads, the cancer cells should be retested for HER2 as well as for hormone receptor status, as these can change from the original diagnosis.

Mar. 25, 2015 See more Expert Answers