The next big advance in cancer treatment could be a vaccine.

After decades of limited success, scientists say research has reached a turning point, with many predicting more vaccines will be out in five years.

These aren't traditional vaccines that prevent disease, but shots to shrink tumors and stop cancer from coming back. Targets for these experimental treatments include breast and lung cancer, with gains reported this year for deadly skin cancer melanoma and pancreatic cancer.

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"We're getting something to work. Now we need to get it to work better," said Dr. James Gulley, who helps lead a center at the National Cancer Institute that develops immune therapies, including cancer treatment vaccines.

More than ever, scientists understand how cancer hides from the body's immune system. Cancer vaccines, like other immunotherapies, boost the immune system to find and kill cancer cells. And some new ones use mRNA, which was developed for cancer but first used for COVID-19 vaccines.

For a vaccine to work, it needs to teach the immune system's T cells to recognize cancer as dangerous, said Dr. Nora Disis of UW Medicine's Cancer Vaccine Institute in Seattle. Once trained, T cells can travel anywhere in the body to hunt down danger.

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"If you saw an activated T cell, it almost has feet," she said. "You can see it crawling through the blood vessel to get out into the tissues."

Patient volunteers are crucial to the research.

Kathleen Jade, 50, learned she had breast cancer in late February, just weeks before she and her husband were to depart Seattle for an around-the-world adventure. Instead of sailing their 46-foot boat, Shadowfax, through the Great Lakes toward the St. Lawrence Seaway, she was sitting on a hospital bed awaiting her third dose of an experimental vaccine. She's getting the vaccine to see if it will shrink her tumor before surgery.

"Even if that chance is a little bit, I felt like it's worth it," said Jade, who is also getting standard treatment.

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Progress on treatment vaccines has been challenging. The first, Provenge, was approved in the U.S. in 2010 to treat prostate cancer that had spread. It requires processing a patient's own immune cells in a lab and giving them back through IV. There are also treatment vaccines for early bladder cancer and advanced melanoma.

Early cancer vaccine research faltered as cancer outwitted and outlasted patients' weak immune systems, said Olja Finn, a vaccine researcher at the University of Pittsburgh School of Medicine.

"All of these trials that failed allowed us to learn so much," Finn said.

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As a result, she's now focused on patients with earlier disease since the experimental vaccines didn't help with more advanced patients. Her group is planning a vaccine study in women with a low-risk, noninvasive breast cancer called ductal carcinoma in situ.

More vaccines that prevent cancer may be ahead too. Decades-old hepatitis B vaccines prevent liver cancer and HPV vaccines, introduced in 2006, prevent cervical cancer.

In Philadelphia, Dr. Susan Domchek, director of the Basser Center at Penn Medicine, is recruiting 28 healthy people with BRCA mutations for a vaccine test. Those mutations increase the risk of breast and ovarian cancer. The idea is to kill very early abnormal cells, before they cause problems. She likens it to periodically weeding a garden or erasing a whiteboard.

Others are developing vaccines to prevent cancer in people with precancerous lung nodules and other inherited conditions that raise cancer risk.

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"Vaccines are probably the next big thing" in the quest to reduce cancer deaths, said Dr. Steve Lipkin, a medical geneticist at New York's Weill Cornell Medicine, who is leading one effort funded by the National Cancer Institute. "We're dedicating our lives to that."

People with the inherited condition Lynch syndrome have a 60% to 80% lifetime risk of developing cancer. Recruiting them for cancer vaccine trials has been remarkably easy, said Dr. Eduardo Vilar-Sanchez of MD Anderson Cancer Center in Houston, who is leading two government-funded studies on vaccines for Lynch-related cancers.

"Patients are jumping on this in a surprising and positive way," he said.

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Drugmakers Moderna and Merck are jointly developing a personalized mRNA vaccine for patients with melanoma, with a large study to begin this year. The vaccines are customized to each patient, based on the numerous mutations in their cancer tissue. A vaccine personalized in this way can train the immune system to hunt for the cancer's mutation fingerprint and kill those cells.

But such vaccines will be expensive.

"You basically have to make every vaccine from scratch. If this wasn't personalized, the vaccine could probably be made for pennies, just like the COVID vaccine," said Dr. Patrick Ott of Dana-Farber Cancer Institute in Boston.

The vaccines under development at UW Medicine are designed to work for many patients, not just a single patient. Tests are underway in early and advanced breast cancer, lung cancer and ovarian cancer. Some results may come as soon as next year.

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Todd Pieper, 56, from suburban Seattle, is participating in testing for a vaccine intended to shrink lung cancer tumors. His cancer spread to his brain, but he's hoping to live long enough to see his daughter graduate from nursing school next year.

"I have nothing to lose and everything to gain, either for me or for other people down the road," Pieper said of his decision to volunteer.

One of the first to receive the ovarian cancer vaccine in a safety study 11 years ago was Jamie Crase of nearby Mercer Island. Diagnosed with advanced ovarian cancer when she was 34, Crase thought she would die young and had made a will that bequeathed a favorite necklace to her best friend. Now 50, she has no sign of cancer and she still wears the necklace.

She doesn't know for sure if the vaccine helped, "But I'm still here."