Worldwide, breast cancer is the most common cancer for women, with 1 in 8 women being diagnosed with breast cancer during their lifetime. 

HER2-positive breast cancer

About 1 in 5 women with breast cancer have a specific type called HER2-positive breast cancer. “HER2-positive” describes an abnormally high presence of HER2 proteins on cancer cells. HER2 proteins help breast cells grow and repair, so an overexpression of HER2 proteins leads to rapid breast cancer cell reproduction. For this reason, HER2-positive cancers are particularly aggressive forms of breast cancer. HER2-positive cancers are also more likely to recur. 

Existing treatments: Herceptin and Kadcycla

Approved by the FDA in 1998, Herceptin (i.e., trastuzumab) is a receptor antagonist that blocks growth signals from reaching cancer cells. Herceptin increases overall survival time and decreases likelihood of cancer reccurrence in women with HER2-positive breast cancer. In 2013, emtansine (a chemotherapy drug) was added to trastuzumab, which further increased survival rates for women with metastatic breast cancer. This combination of trastuzumab and emtansine is called Kadcyla (ado-trastuzumab emtansine). Unfortunately, about half of women with breast cancer do not respond to Herceptin or Kadcyla.

A new option: GP2 immunotherapy

A biopharmaceutical company called Greenwich LifeSciences developed GP2, a peptide that helps immune cells find and destroy HER2-positive cancer cells. GP2 is administered along with GM-CSF, an FDA-approved immune response stimulator. Together, GP2 and GM-CSF (i.e., GP2 immunotherapy) prevent recurrence of breast cancer in patients who have already been treated with Herceptin. 

The phase 2 clinical trial

The phase 2 clinical trial included 96 patients with HER2-positive breast cancer who completed Herceptin treatment after breast cancer surgery. Among these patients, 46 received Greenwich LifeSciences’ GP2 immunotherapy, which included 6 to 10 intradermal GP2+GM-CSF injections over a period of 6 months to a year. The other 50 patients received placebo injections of only GM-CSF.

Promising 5-year results

Within 5 years, approximately 11% of patients in the placebo (GM-CSF only) group had a recurrence of breast cancer. Alternatively, not a single patient in the GP2 immunotherapy group developed breast cancer again.