Study suggests colon cancer vaccine possible

WASHINGTON (Reuters) - A protein found only in the intestines may help lead the way to a vaccine that can treat colon cancers and perhaps other tumors too, U.S. researchers reported on Tuesday.

Mice immunized with the protein and then infected with colon tumors had fewer tumors spread to the lung and liver than usual, they reported in the Journal of the National Cancer Institute.

Many cancer vaccines are in the works but researchers are struggling to find the right targets, called antigens, that are found only on tumors and not in healthy tissue.

Adam Snook and Dr. Scott Waldman of Thomas Jefferson University in Philadelphia and colleagues decided to look at colon cancer in particular because the intestinal lining and some other so-called mucosal areas are protected from much of the activity of the immune system.

Also, some proteins from these immune-protected sites are active on tumor cells.

They looked specifically at guanylyl cyclase C protein, or GCC protein, normally only expressed, or active, in the intestinal lining and in spreading colorectal cancer cells.

The researchers injected mice with colon cancer cells before or after immunization with guanylyl cyclase C.

Unvaccinated animals had an average of 30 new tumors in the lungs and liver. Vaccinated animals had three. While such an approach does not look like a cure, it could be an important treatment, they said.

"More than 50 percent of patients with colorectal cancer die of metastatic disease, primarily in the liver and lung," they wrote. The vaccinated mice also lived longer.

Colon cancer affects an estimated 1.2 million new patients a year globally and kills 130,000.

While injecting mice with tumor cells causes cancer, it does not perfectly replicate human cancer development, researchers caution. It is far easier to treat such a mouse in the lab than a person with cancer.

But the researchers are hopeful.

"We think this identifies a novel class of vaccine candidate targets for tumors that originate and metastasize from mucosa, like colorectal cancer," Waldman said in a statement.

The approach may also work in cancers of the head and neck, lung, breast, vagina and bladder, all of which begin in the mucosa, they said.

Cancer vaccines that have shown more promise include one made by Antigenics Inc against melanoma, the deadliest form of skin cancer, and another made by Avant Immunotherapeutics Inc and licensed by drug giant Pfizer Inc that attacks glioblastoma multiforme, the most common and deadly type of brain tumor.

Cuban scientists said on Tuesday they had made available a vaccine that extends the lives of lung cancer patients.

(Editing by Eric Beech)