Breast Cancer Vaccine Shows Promise in Early Human Trial

An experimental vaccine appears promising at preventing the recurrence of an aggressive form of breast cancer.

In a decade-long Phase I human trial of 66 patients, the vaccine prolonged the life of about 80% of the study participants with late-stage human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The results were published in JAMA Oncology this month.

Existing treatments for HER2-positive breast cancer, including monoclonal antibodies and chemotherapy, can be unsafe or ineffective. Some treatments must be given frequently for a long time. Vaccines, on the other hand, need not be administered so often and have the potential to prevent the cancer from coming back.

About 288,000 women and 2,700 men in the United States are diagnosed with breast cancer each year and some 48,000 people die of the disease. According to the American Cancer Society, about 14% of people with breast cancer are HER2-positive.

Breast cancer cells with high levels of HER2 tend to grow and spread faster than HER2-negative breast cancers. Patients with HER2-positive breast cancer may have a poorer response to older chemotherapy agents and a lower risk of survival.

Over 80% of the participants who received the medium-dose vaccine were still living a decade later. And 40% of those patients never had a recurrence.

“This is a really nice study because, in essence, they’ve shown that their vaccine can induce a nice HER2-specific immune response,” William Gillanders, MD, professor and vice-chair in the Department of Surgery at Washington University in St. Louis School of Medicine, told Verywell.

“Cancer vaccines are extremely safe. They don’t have any of the side effects of other standard treatments for cancer,” Gillanders said. “Based on what we’re learning about the immune system and cancer, these vaccines may be just as effective as some of these other treatments that patients dread so much.”

How the Vaccine Works

The study included 66 patients who were treated between 2001 and 2010. They were divided into three groups with each receiving either 10, 100, or 500 micrograms of the vaccine. Researchers administered the vaccine intradermally once a month for three months.  

This DNA-based vaccine contains the genetic code to make the HER2 protein, along with other compounds that boost the immune response. The cells in the arm absorb that DNA and start pumping out copies of HER2.

The immune system recognizes the protein as foreign and dangerous and creates defense mechanisms against it. The next time the immune system encounters a cancer cell with a HER2 protein, it’s already primed to snuff it out.

“While we can get rid of detectable cancer with standard treatment of HER2 cancer, there still may be small amounts of cells that can survive,” Mary “Nora” Disis, MD, lead author of the study and a professor at the University of Washington School of Medicine, told Verywell in an email. “The vaccine helps the immune system detect and destroy any remaining cells—helping prevent recurrence of the cancer.”

After four months and nine months, researchers performed a biopsy at the site of vaccination to measure the longevity of the immune response. Those who got the highest dosage of vaccine tended to have the most lasting immune response. However, those who got the second-highest dose were more likely to survive in the decade after being immunized.

“The data from the highest dose… shows that we don’t want the DNA to stick around for too long,” Disis said. “Having too much stimulation of the immune system, in that case, might lead to a reduced response over time.”

All of the patients with stage III cancer who received the 100-microgram dose were still alive after a decade of follow-up. When including those with stage IV cancer, about 80% survived, Disis said.

Overall, the most common side effects included redness and swelling at the injection site and flu-like symptoms, which generally resolved in 48 hours. While some patients had severe side effects, the researchers say they may have been related to other treatments the patients were taking. Most of the study participants had previously been treated with trastuzumab or were currently on the chemotherapy infusion medication.

“The results show the vaccine is very safe. In fact, the most common side effects that we saw in about half the patients were very similar to what you see with the COVID-19 vaccine,” Disis said.

Vaccines Could Revolutionize Breast Cancer Prevention and Treatment

In recent years, interest in cancer vaccines has grown as researchers learn more about how the immune system can fight cancer.

“Engaging the immune system to fight cancer has a lot fewer side effects than chemotherapy or radiation therapy or surgery,” Gillanders said. “There are some cancers where chemotherapy never worked. But now the immunotherapy is working, and it’s really kind of opened the door to a lot of new treatments for patients who didn’t have any good treatments available.”

Cancer vaccines can be used alongside other promising new treatments which also harness the immune system, such as a type of drug called immune checkpoint inhibitors, Gillanders said.

There are many breast cancer vaccines currently undergoing testing, including more than a dozen that target HER2. While most of the vaccines are intended as treatments, some teams, including Disis’, are studying how they can be used for prevention as well.

Creating a preventive vaccine for people at high risk of certain cancers can be more challenging, Gillanders said, because scientists must be sure the vaccine is entirely safe before immunizing healthy individuals.

Disis said her team’s vaccine is now being tested in a Phase II clinical trial. Researchers are recruiting nearly 150 patients who have low levels of HER2 and are negative for estrogen receptor and progesterone receptor. The trial will likely take about three years to complete. Depending on the success of that trial, the vaccine will then be tested in a Phase III trial.

“This vaccine, along with our other breast cancer vaccines, are part of our mission to end this disease by targeting all subtypes of breast cancer,” Disis said.