(CNN) The US Food and Drug Administration has granted its first approval to an immunotherapy regimen for breast cancer, the agency announced Friday.

The treatment received accelerated approval for triple-negative breast cancer that is locally advanced or metastatic, that cannot be surgically removed and whose cells include a protein called PD-L1. It comprises a combination of immunotherapy and chemotherapy: Tecentriq and Abraxane, respectively.

The FDA's decision comes after an October study published in the New England Journal of Medicine found that the therapy extended progression-free survival -- the amount of time in which a patient's cancer does not worsen. In the PD-L1 subgroup, the median progression-free survival for those receiving the combination treatment was 7.4 months, versus 4.8 months for those getting the chemotherapy with placebo, according to the FDA's announcement . The trial was funded by Genentech Inc., the maker of Tecentriq.

"This is the first time immunotherapy has worked in such a difficult to treat cancer, and is a huge step forward for these breast cancer patients," lead study author Dr. Peter Schmid of Queen Mary University of London said in an October statement.

Dr. Otis Brawley, Bloomberg Distinguished Professor of oncology and epidemiology at Johns Hopkins University, said the FDA's decision to grant the treatment accelerated approval was "the right thing to do" but cautioned that it's not the end of the story.