Mayo Clinic researchers have announced the discovery of a mechanism that blocks the body's natural ability to reject breast cancer. They also described an experimental therapy to remove that block. The findings were announced in a news conference at a major gathering of breast cancer specialists, the Era of Hope - Department of Defense Breast Cancer Research Program meeting in Philadelphia.

The goal of the research is to prevent breast cancer recurrence in women who've already experienced remission of the disease. In cases where cancer has spread outside the breast, the 10-year relapse rate can be as high as 90 percent.

Mayo Clinic researchers, collaborating with colleagues at the University of Washington, showed that their experimental therapy to remove the block did not harm the immune system. In fact, it boosted it. Mice that received the toxic injections that killed the immune system blockages had tumors that were one-tenth the size of mice that did not receive the injections.

Breast cancer researchers have known for years that the body's immune system is naturally poised to reject breast cancer. However, in breast cancer patients, something interferes with this rejection, allowing the cancer to grow unchecked. This new finding helps unlock that mystery and may lead to safer, gentler therapies.

"Evidence is emerging that some of the effects of chemotherapy are due to depleting T-regulatory (T-reg) cells," says Keith Knutson, Ph.D., the Mayo Clinic immunology researcher who led the study. "The strategy we use in our investigation may actually be a way to target the T-regs directly, without using the indirect route of chemotherapy. Depleting T-regulatory cells may boost natural immunity against breast cancer."

The Mayo Clinic and University of Washington collaborative study is the first to show these two new important aspects of breast cancer:

• T-regulatory cells play a disease-promoting role in breast cancer.
• T-regs can be selectively and therapeutically eliminated without harming the immune response of white blood cells. Instead, blocking T-regs boosts natural immunity.

Knutson emphasized that further studies must validate these findings before they can be applied to human breast cancer patients.

SOURCE:
Mayo Clinic (http://www.mayo.edu)