University of Pittsburgh researchers have successfully prompted the immune system to go after colon cancer in its earliest stages for those at high risk. The results of a clinical trial show that colon cancer may be the newest target for an effective anti-cancer vaccine.

They reported the promising results of the first human clinical trials to prevent colon cancer with a vaccine in the January issue of the journal Cancer Prevention Research. The study was partially funded by the National Cancer Institute and the National Institutes of Health.

Colorectal cancer is the No. 3 cause of cancer deaths in the United States, striking more than 100,000 Americans each year, according to the American Cancer Society, which says that over a lifetime an individual has a 5 percent chance of developing it. Each year, nearly 52,000 die from it.

"This prophylactic colon cancer vaccine boosts the patient's natural immune surveillance, which potentially could lead to the elimination of premalignant lesions before their progression to cancer," said Olivera Finn, distinguished professor and chair of the Department of Immunology at Pitt's School of Medicine, who is also the vaccine's developer, in a written statement. "This might spare patients the risk and inconvenience of repeated invasive surveillance tests, such as colonoscopy, that currently are used to spot and remove precancerous polyps."

For the study, the researchers tested the vaccine in patients who had a previous history of a well-developed precancerous polyp, called an advanced adenoma, which is how colon cancer typically develops. When such polyps are found, they are removed so they cannot become cancerous.

"Around 30 to 40 percent of these patients will develop a new polyp within three years," Dr. Robert E. Schoen, professor of medicine and epidemiology in Pitt's Division of Gastroenterology, Hepatology and Nutrition and the study's clinical leader, said. "In this study, we demonstrated the ability of the vaccine to boost immunity. Subsequent trials need to evaluate the vaccine for its ability to lower or prevent polyp recurrence and thus progression to colon cancer."

According to the university's explanation, the Pitt vaccine targets an abnormal variant of a protein called MUC1 that the cell itself makes. In advanced adenomas and in cancer, that protein is made with great abundance. MUC1, it noted, is also abnormally present in pancreatic, breast, lung and prostate cancer, which may mean a vaccine that targets it will have impact there, as well.

Business Insider said plans were in the works to test the vaccine against those cancers, too.

The Pittsburgh team tested the vaccine in 39 patients ages 40 to 70 that did not have cancer, but did have a history of the polyps. "It produced a strong protective response in 17 of the patients, or 44 percent," they said in a news release on the study. "Researchers said the lack of response in the other 22 patients was likely due to already high levels of cells that suppress the immune system's ability to fight cancer."

Finn theorized that it might be better to vaccinate people against colon cancer at even earlier stages or only vaccinate those without an already-suppressed immune system.

In the study, patients received an initial dose, then more shots of vaccine two and 10 weeks later. Blood tests showed the response at those times, and at 12 weeks, 28 weeks and a year. At that point, a booster shot was given to "confirm the durability of the immune response."

There were few side effects reported and they were mild, the researchers noted. Safety was previously shown in patients with pancreatic cancer.

Not all colorectal tumors produce abnormal MUC1, Schoen told MIT Technology Review, and there’s no way to tell in advance which ones will. That means it could still be theoretically possible to develop cancer even with an effective vaccine. A patient might be at risk for tumors that don't make the excessive MUC1 the vaccine targets.

That means it's not clear if the vaccine could make colonoscopies unnecessary, Mack Ruffin IV, professor of family medicine and a research scientist in epidemiology at the University of Michigan, told the MIT publication. “If they still need colonoscopies, we haven’t done anything but add extra cost and side effects to managing people with polyps.”

News of the possible vaccine comes at a time when cancer deaths are decreasing slightly. Science Daily reported this week that overall cancer death rates have been declining since the early 1990s, based on a report from the American Cancer Society, the Centers for Disease Control and Prevention, the National Cancer Institute and the North American Association of Central Cancer Registries. Their collaborative report is published online in the Journal of the National Cancer Institute.

Between 2000 and 2009, cancer death rates dropped by 1.8 percent per year among men and by 1.4 percent per year among women. Death rates among children up to 14 years of age also continued to decrease by 1.8 percent each year. Men saw decreases in 10 of the 17 most common cancers: lung, prostate, colon and rectum, leukemia, non-Hodgkin lymphoma, kidney, stomach, myeloma, oral cavity and pharynx, and larynx, while liver, pancreas and skin melanoma cancers increased.

At the same time, fewer women died of 15 of the 18 most common cancers: lung, breast, colon and rectum, ovary, leukemia, non-Hodgkin lymphoma, brain and other nervous system, myeloma, kidney, stomach, cervix, bladder, esophagus, oral cavity and pharynx, and gallbladder. Death rates for pancreas, liver and uterine cancer rose.