Breast Cancer Vaccines: How Researchers Are Testing Prevention in Clinical Trials

Says BCRF investigator Dr. Olivera Finn: “Without BCRF support, there would be no trial today.”

Breast cancer vaccines are an expanding area of research aimed at preventing cancer before it develops. BCRF-supported researchers like Dr. Olivera Finn are making significant progress in developing vaccines for breast cancer and bringing them to clinical trials.

For more than three decades, Dr. Finn has pursued a vaccine to prevent cancer. And now, thanks to pivotal BCRF funding, she’s testing one in a breast cancer clinical trial.

“Without BCRF support, there would be no trial today,” Dr. Finn said.

Is there a breast cancer vaccine?

While there is currently no widely available breast cancer vaccine, researchers such as Dr. Finn are actively developing vaccines designed to prevent the disease. These vaccines aim to train the immune system to recognize and destroy cancer cells before they grow or spread. Vaccines designed to treat breast cancer are also in the works.

Several breast cancer vaccine clinical trials are now underway, exploring how these approaches can target early-stage or precancerous cells. One promising area of research focuses on preventing progression from conditions like ductal carcinoma in situ (DCIS) to invasive breast cancer. DCIS is a non-invasive, pre-cancerous lesion that plays a critical role in breast cancer prevention research.

In 2024, Dr. Finn and her team at the University of Pittsburgh School of Medicine and UPMC Hillman Cancer Center launched a phase 1 clinical trial testing the first breast cancer vaccine designed to train the immune system to target DCIS before it can progress to invasive cancer.

Dr. Finn initially planned to launch this clinical trial with a $100,000 grant from the Pittsburgh-based A Glimmer of Hope Foundation—but she knew she needed to promptly secure more funding to enroll more than a few patients. That’s when BCRF invited her to apply for funding through its Precision Prevention Initiative, ultimately awarding her a $2.1 million grant. 

“The opportunity to apply came at precisely the right time, and the money came very fast so we could launch,” she said. “For clinical trials, that is crucial. We would still be looking for funding otherwise.”

What is DCIS, and why is it a focus for breast cancer prevention?

Ductal carcinoma in situ (DCIS) is an early, non-invasive form of breast cancer where abnormal cells are confined to the milk ducts, making it an attractive target for prevention and early intervention research.

While DCIS—also known as stage 0 breast cancer—is non-invasive, it is considered precancerous because it can develop into invasive breast cancer in an estimated 20 to 50 percent of cases if left untreated. An estimated 50,000-60,000 women are diagnosed with DCIS each year.

Today, when a woman is diagnosed with DCIS, she’s typically treated as though she has stage 1 breast cancer: with a lumpectomy and radiation, plus hormone therapy for those with hormone receptor-positive DCIS. About 98 percent of women treated for DCIS are alive 10 years later, so stage 0 breast cancer has an excellent prognosis.

But DCIS treatment is controversial: An estimated 50 to 80 percent of DCIS diagnoses never become invasive breast cancer, so many women are over-treated every year. A vaccine like the one Dr. Finn developed could drastically reduce such over-treatment and potentially prevent the disease entirely in women whose DCIS would have become invasive otherwise.

In this phase 1 trial, patients are getting the vaccine along with standard-of-care treatment. If the results from this trial show that the vaccine is strongly immunogenic—meaning it can stimulate an immune response—Dr. Finn hopes a future trial will test the vaccine plus standard-of-care treatment, but without surgery. That would determine if a woman’s own immune system, strengthened by the vaccine, could eliminate DCIS and prevent progression to breast cancer.

The making of a cancer vaccine

The vaccine Dr. Finn developed trains the immune system to target an abnormal version of the MUC1 protein (called the MUC1 antigen) that’s produced by cells of more than 80 percent of cancers, including breast. Dr. Finn first discovered that the human immune system could recognize this MUC1 antigen more than 30 years ago, and knowing its potential for prevention, has pursued this research since.

“We published on MUC1 in 1989, and we went into clinical trials in 1993, four years later. Everybody was eager,” she said. “But we were not getting the results we wanted in patients with advanced cancer even though we were getting good results in laboratory models.”

Dr. Finn and her team kept working at it, though, and their persistence started to pay off. In the early 2000s, they launched the first clinical trial testing the MUC1 vaccine in people with a history of advanced adenomas: colorectal polyps that can raise a person’s risk of developing colorectal cancer. When these patients were given the MUC1 vaccine, Dr. Finn reported in 2013, they had a strong immune response and immune memory and were protected from developing new polyps. She continued expanding her research, investigating MUC1 in several cancers.

“We kept testing hypotheses and marching forward,” she said. “And around us there were tremendous developments in other fields and in immunology—new techniques and technologies. We were convinced that all the testing we did and all the hypotheses we developed along the way were moving us in the right direction—we just needed the capacity to do this effectively. We could see it on the horizon. And now here we are.”

The future of breast cancer prevention vaccines

Breast cancer vaccines represent a promising shift toward preventing cancer before it develops. By targeting precancerous changes and training the immune system to stop disease progression early, these approaches have the potential to reduce over-treatment and improve outcomes for thousands of patients.

Progress like this depends on sustained investment in research. Breakthroughs such as Dr. Finn’s vaccine are made possible through funding that allows scientists to move from early discovery into clinical trials. Continued support is essential to advancing this work and bringing breast cancer prevention vaccines closer to reality.

Dr. Finn noted that funding, especially for prevention research, can be hard to come by, making BCRF’s work stand out.

“It’s striking that BCRF is focused on prevention,” she said. “Prevention research is underfunded, but it’s the hope of the world. It’s so important that BCRF recognizes this.”

Help fund the research driving these breakthroughs and support the development of life-saving innovations.