Thousands more women with breast cancer could benefit from a popular immunotherapy drug than previously thought, research suggests.
Pembrolizumab, sold under the brand name Keytruda, targets and blocks a specific protein on the surface of certain immune cells that then seeks out and destroys the cancer cells.
In England, it is offered to those with triple-negative breast cancer, one of the most aggressive forms of the disease, which accounts for around 15% of cases. However, new findings from a global trial suggest that it may be effective when used more widely.
The findings will be presented at the European Breast Cancer Conference in Milan on Wednesday.
Treating a common form of breast cancer with pembrolizumab, as well as chemotherapy, before and after surgery can be effective regardless of the patient’s age or if they have gone through menopause, researchers have found.
They tested the drug on women with early-stage breast cancer that has a high risk of recurrence or spread, and that is estrogen receptor positive (ER positive) and HER2 negative.
According to Cancer Research UK, around 80 out of 100 breast cancer diagnoses are ER-positive.
The Keynote-756 trial has been ongoing internationally for eight years and consists of 1,278 patients with invasive ductal carcinoma (IDC), which means that cancer has started to spread from the milk ducts and into the surrounding breast tissues.
Patients were either treated with pembrolizumab and chemotherapy before and after surgery, or with a placebo. Researchers measured the lack of cancer signs in tissue samples, also known as a pathologic complete response (PCR) rate.
Prof Javier Cortés, the director of the International Breast Cancer Center in Barcelona, Spain, said there was a “statistically significant increase” in PCR rate among those treated with pembrolizumab.
About 24.3% of patients had no cancer cells in the breast or lymph nodes, compared with 15.6% of patients treated with a placebo.
Dr Simon Vincent, the director of research, support and advocacy at the UK charity Breast Cancer Now, said: “This exciting study shows that adding pembrolizumab to chemotherapy before and after surgery can be more effective at killing cancer cells at women with the most common type of breast cancer, ER-positive HER2-negative, regardless of their age or menopausal status.
“The trial found that pembrolizumab resulted in more patients having no detectable cancer cells in their breast or lymph nodes when their treatment was completed, although further research is needed to see if this translates into improved survival rates and a lower likelihood of the cancer comes back.
“With more than 1,000 people dying from breast cancer every month in the UK, we desperately need new and effective treatments for this disease.
“While pembrolizumab is currently used for the treatment of triple negative breast cancer, we hope that the drug can be submitted to the MHRA [Medicines & Healthcare products Regulatory Agency] for licensing and assessed by Nice [National Institute for Health and Care Excellence] as soon as possible so that patients with ER-positive HER2-negative breast cancer, who can also benefit from this treatment, can get it on the NHS.”
The conference will also hear how researchers have developed a genetic test that can identify how patients with triple negative early stage breast cancer will respond to immunotherapy drugs. This means that patients who are unlikely to respond to these drugs can avoid the adverse side effects associated with them and be treated with other therapies.
