Up to 20 percent of breast cancers overexpress the HER2/neu gene. In other words, they are HER2+. The HER2/neu gene has an important role in the signal transduction pathways leading to cell growth and differentiation, which accounts for the reputation of aggressiveness of this type of breast cancer.
However, the development of Herceptin, which is used to treat HER2+ breast cancer, has markedly improved the prognosis of this type of breast cancer. HER2+ disease can be estrogen receptor positive (ER+) and/or progesterone receptor positive (PR+), however it is somewhat more likely to be ER-/PR-. Asian American women are more likely to develop HER2+ disease than white, African-American or Latina women.

High BMI can reduce survival

Overall survival and time to progression have been reported to decrease with increasing body mass index (BMI) among women with HER2 overexpressing breast cancer. Obesity and type 2 diabetes both appear to predict worse outcomes in HER2+ patients. Use of the anti-diabetes drug metformin is associated with better prognosis among women with HER2+ breast cancer. Recent evidence suggests that treating with Herceptin concurrently with chemotherapy may potentially equalize disease free survival rates between obese and normal weight women with HER2+ breast cancer.

HER2 positive breast cancer may also be EGFR positive

A study designed to investigate the association between epidermal growth factor receptor (EGFR) expression and aggressive breast cancer that is resistant to systemic therapy found that EGFR-positive tumors were more likely to be HER2 overexpressing. EGFR expression was linked to poor breast cancer prognosis in the study. Therefore, blocking EGFR might improve outcome in selected HER2+ patients.

Breast conserving surgery not appropriate for multifocal HER2 positive breast cancer

While many physicians recommend mastectomy in cases of multifocal or multicentric breast cancer (under the assumption that there is greater risk of poor local control with less extensive surgery), there appear to be some circumstances under which lumpectomy or partial mastectomy does not reduce survival. However, one study found that HER2+ disease was associated with a far higher rate of local breast cancer recurrence (in the same breast as the original tumors) than HER2- disease. Therefore, breast cancer patients with HER2+ multifocal disease are not good candidates for breast conserving treatment.

Additional comments

Please also see our articles on breast cancer diet for HER2+ patients and survivors and HER2+ prognosis. HER2 overexpressing breast cancer patients and survivors can also refer to their articles concerning their hormone receptor subtype (e.g., ER-/PR-, ER+/PR-).
Below are links to recent studies on this topic. For a more complete list of studies, please click on HER2+.