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Vaccine Triggers Immune Response to Early Signs of Colon Cancer

First test in humans of vaccine based on tumor proteins (Jan. 7)

A first-of-its-kind vaccine developed by researchers at the University of Pittsburgh Cancer Institute has successfully prompted the immune system to respond to early indications of colon cancer in people at high risk for the disease.

The results of the first human clinical trials of the new vaccine were reported in Cancer Prevention Research and are available online.

“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, PhD. “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.”

The colon cancer vaccine is directed against an abnormal variant of a self-made cell protein called MUC1, which is altered and produced in excess in advanced adenomas and in cancer. MUC1 also is abnormally present in pancreatic, breast, lung, and prostate cancer.

Prior to the new study, no vaccine based on cell proteins made by tumors had been tested in humans to prevent cancer. Preclinical models had shown, however, that the vaccine works by targeting the abnormal cells that grow the cancer.

The new vaccine was tested in 39 patients aged 40 to 70 years who had a history of advanced adenomas (intestinal polyps with the potential to become cancerous), which put these individuals at increased risk for subsequent colorectal cancer. The vaccine produced a strong protective response in 17 (44%) of the patients. The researchers said that the lack of response in the other 22 patients was likely due to high levels of cells that suppress the immune system’s ability to fight cancer.

“This suggests that it might be better to vaccinate people against colon cancer at an even earlier stage, or vaccinate only people who do not already have suppressed immune systems,” Finn said.

The patients in the clinical trial received an initial dose of the vaccine and then additional injections 2 and 10 weeks later. Blood samples were drawn to measure the patients’ immune responses at those time points, as well as 12 weeks, 28 weeks, and 1 year later. A booster injection was given at 1 year to confirm the durability of the immune response.

The vaccine was well tolerated and safe. Side effects included red skin and discomfort at the injection site, and flu-like symptoms after the first injection.

Colorectal cancer is the third leading cause of cancer death in the U.S. The American Cancer Society estimates that 2012 will end with 103,170 new cases of colon cancer and 40,290 new cases of rectal cancer. The overall lifetime risk of developing colorectal cancer is 1 in 20.

Source: University of Pittsburgh; January 7, 2013.

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