LONDON — Women with a hard-to-treat form of breast cancer were found to live longer when treated with a combination of chemotherapy and immunotherapy drugs.

CNN reports that triple negative breast cancer is an aggressive form of the disease in which cancer cells lack receptors for estrogen, progesterone, and HER2 — making it unresponsive to certain treatments.

Cancer cells can be treated with chemotherapy, but often develop resistance to it, allowing them to spread to other body parts. Patients usually survive 18 months or less.

A new study published in the New England Journal of Medicine found that treatment combining chemotherapy with the immunotherapy drug Tecentriq was more effective, improving overall survival rates by almost four months.

In the clinical trial, 902 women treated at 246 medical centers in 41 countries were randomly assigned either Tecentriq and chemo, or a placebo and chemo.

Chemotherapy was given once a week while the immunotherapy drug was administered intravenously every two weeks.

The drug deactivates a protein in the cancer cells which keeps it safe from the immune system, while chemotherapy roughens up its surface, enabling the immune system to recognize and attack the cancer.

The new treatment is currently being reviewed, and may well become the first FDA-approved immunotherapy drug to treat breast cancer, reports the New York Times.