An immunotherapy/chemotherapy combo drug can help early-stage breast cancer patients remain cancer-free following treatment, a new trial shows.

The combo drug, Kadcyla, is already approved to treat patients with advanced HER2-positive breast cancer, researchers said.

The new results show that stage 1 breast cancer patients who received Kadcyla stayed free of invasive cancer five years after treatment.

“One year of [Kadcyla] after surgery for patients with a stage 1 HER2-positive cancer leads to outstanding long-term outcomes, making it a reasonable treatment approach for select patients,” said senior study author Dr. Sara Tolaney, chief of breast oncology at Dana-Farber Cancer Institute in Boston.

HER2-positive breast cancers are fueled by a protein that normally helps control cell growth. Cancer cells that make too much HER2 might grow more quickly and are more likely to spread to other parts of the body.

Patients with early HER2-positive breast cancer have their cancers return 5% to 30% of the time following initial treatment, said lead researcher Dr. Paolo Tarantino, also with Dana-Farber.

The immunotherapy drug trastuzumab helps inhibit HER2-positive cancers by blocking that protein. When given alongside chemotherapy after breast cancer surgery, trastuzumab can significantly reduce the risk cancer will recur in these patients, Tarantino said.

“But the side effects can have a detrimental impact on patients' quality of life.” Tarantino added.

Kadcyla is a single drug that combines trastuzumab with the chemo drug emtansine. It was developed to provide the benefits of chemotherapy and immunotherapy while limiting toxic side effects.

For the new clinical trial, researchers recruited 512 patients at cancer centers across the United States, with 384 receiving Kadcyla and 128 treated with chemo alongside trastuzumab.

Five years after treatment, 97% of patients who got Kadcyla had no evidence of cancer recurrence.

The rate of toxic side effects were similar between the two groups, but patient-reported outcomes showed better quality of life with Kadcyla, researchers said.

Patients had less nerve damage, less hair loss and better work productivity with Kadcyla than with chemo and trastuzumab given separately.

The trial was funded in part by Genentech, the maker of Kadcyla.

The results were published June 27 in the Journal of Clinical Oncology.