Treating Metastatic Breast Cancer with Immunotherapy: Understanding the Breakthrough

Metastatic breast cancer is the most advanced stage of breast cancer (also known as stage IV), which means the cancer has spread beyond the breast to other distant parts of the body.

While metastatic breast cancer can’t be cured and is more difficult to treat than early-stage breast cancer, there are many FDA-approved treatment options for metastatic breast cancer available, as well as ongoing research to improve upon current therapies, called clinical trials.

“I always tell patients about all the recent new medications that are targeted, that are brilliant, that are helping people,” says Amy Tiersten, MD, a hematologist and oncologist at the Mount Sinai Hospital in New York City. “It’s just a really promising time to have metastatic breast cancer because people can do well for a long period of time with good quality and quantity of lives.”

Clinical Trials for Metastatic Breast Cancer: Immunotherapy

Breast cancer has historically been considered immunologically silent. New clinical trials and preclinical trials suggest, however, that a treatment called immunotherapy is changing that.

Immunotherapy drugs use the body’s own immune system to attack cancer cells. “Cancer cells have a way of putting a break on the immune system so that the immune system can’t find them and kill them,” says Dr. Tiersten.

Certain types of immunotherapy drugs essentially “take the brakes off” of the immune system to help it kill cancer cells. These drugs belong to a class known as checkpoint inhibitors. “Checkpoint inhibitors are extremely interesting drugs that actually act by jumpstarting a patient’s own immune system to recognize the cancer cells as ‘other,’” says Dr. Tiersten.

What Type of MBC Could Immunotherapy Help Treat?

Checkpoint inhibitors are FDA-approved for treating other cancers, such as lung cancer, melanoma, and kidney cancer. For metastatic breast cancer, checkpoint inhibitors are still in clinical trials. Most of the research has been done on triple-negative breast cancer, a type with cancer cells that don’t have estrogen or progesterone receptors and also don’t make too much of the protein called HER2.

“Immunotherapies work best in cancers that are very mutated and very different from normal cells,” says Dr. Tiersten. “Triple-negative breast cancer cells are the most mutated compared to other subtypes of breast cancer.”

Because triple-negative breast cancer cells don’t have hormone receptors, hormone therapy is not helpful in treating these cancers. And because they don’t have too much of the protein HER2, drugs that target HER2 aren’t helpful either. Chemotherapy, however, can still be useful.

“There are trials that have been done in triple-negative breast cancer and ongoing trials combining the checkpoint inhibitors with chemotherapy,” says Dr. Tiersten. “But the mainstay of treatment is chemotherapy because we don’t have the targeted therapies to different receptors.”

“There’s tons of clinical trials that are looking at the role of newer biologic or targeted therapies to augment the effectiveness of chemotherapy or even use in lieu of chemotherapy for triple-negative breast cancer. It’s a very important area of research,” says Dr. Tiersten

Interested in learning more about or finding a clinical trial for metastatic breast cancer? Click here to use the Cancer Research Institute’s Clinical Trial Finder.