National Cancer Institute Studying Possible Immunotherapy Treatment for Metastatic Breast Cancer

Immunotherapy has gained speed in recent decades as a form of cancer treatment, more helpful for some types of the disease than others. This form of therapy mobilizes a patient’s immune system as a means to attack cancer cells or produces substances similar to the immune system in a lab and uses that to help battle the disease. Now, a clinical trial being conducted by the National Cancer Institute (NCI) has found that a form of this treatment may be beneficial for metastatic breast cancer patients who have run out of other options.

The NCI’s Center for Cancer Research is conducting a trial on an experimental form of immunotherapy that uses a patient’s own tumor-fighting immune cells. This specific treatment utilizes tumor-infiltrating lymphocytes or TILs, which are found in and around the tumor. TILs can mount attacks against cancer cells with proteins called neoantigens, which are produced when mutations occur within tumor DNA.

The NCI says cancers that feature many mutations are generally good targets for immunotherapy. However, breast cancer doesn’t have as many neoantigens and the impacts of TIL therapy against the disease are not as clear. The findings thus far from the trial, published in the Journal of Clinical Oncology, show that this therapy may be beneficial for some patients, however.

Dr. Steven Rosenberg, lead researcher and chief of the Surgery Branch in NCI’s Center for Cancer Research, says, “It’s popular dogma that hormone receptor–positive breast cancers are not capable of provoking an immune response and are not susceptible to immunotherapy. The findings suggest that this form of immunotherapy can be used to treat some people with metastatic breast cancer who have exhausted all other treatment options.”

The clinical trial summarized in the paper included 42 women with metastatic breast cancer. The participants were tested to see if they generated an immune response to their cancer. This is necessary to be a candidate for this type of treatment.

Overall, 67% did have an immune reaction. Researchers then used TIL therapy with six of them. This involved taking the reactive TILs, growing them to large numbers in the lab, and then returning them to the patient via an IV infusion. They also received four doses of the immune checkpoint inhibitor pembrolizumab before the infusion to stop the newly added T cells from being inactivated.

This treatment proved effective at shrinking tumors in three of the six women, one of whom had complete tumor shrinkage and is still cancer-free more than five years later. The other two had shrinkage of 52% and 69% after six months and 10 months, respectively. They did each have a return of the disease, which required a surgical removal. However, they currently have no evidence of cancer five years and 3.5 years later.

The team notes some shortcomings of the study, including that pembrolizumab may have had some influence on patient outcomes. However, they say that this type of treatment alone has not been found to cause sustained tumor shrinkage in hormone receptor-positive metastatic breast cancer.

Dr. Rosenberg says they plan to continue treating these types of patients with TIL therapy as part of the clinical trial. There is hope that it could also branch out to patients with different types of cancer in the future.

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