Protein linked to spread of breast, prostate cancer identified

Scientists have identified and blocked the action of a protein linked to the spread of breast, prostate, and skin cancer cells to the bones. The molecule, called RANKL, is produced in bone marrow. In studies of mice, researchers from Austria and Canada showed that inhibiting the protein could stop the cancerous cells from migrating to the bones.

"RANKL is a protein which tells tumor cells to come to it," said professor Josef Penninger of the Austrian Academy of Sciences in Vienna. "It sits on the bones, and when tumor cells circulate in the body, then RANKL attracts them into the bones.”

Once a cancer has spread beyond its original site in a process known as metastasis, it becomes much more serious and difficult to treat. An estimated 70% of patients with progressive breast cancer and 84% of advanced prostate cancer sufferers develop bone metastases.

The findings, reported in the journal Nature, explain the puzzle of why certain cancers spread to the bones and how interfering with the process could help to prevent the spread of the disease.

When the researchers gave mice with skin cancer a drug that blocked RANKL, the rodents had fewer tumors in their bones than animals who were not treated. But the drug did not slow the spread of the cancer to other sites in the body.

Penninger and his colleagues stressed that although the research was done in mice, drugs that interfere with RANKL are in development and could be used to test their findings and show if the same holds true for humans. "This is an idea that can be directly tested," Penninger added.

Nearly all breast cancer tumors in women have the receptor for RANKL, which Penninger said is an indirect indication that the findings are relevant to humans.

"Since there are novel inhibitors of RANKL far along in clinical development, the idea is that people who have cancer that is known to spread to bone can start taking this drug when they are diagnosed," said D. Holstead Jones of the University of Toronto, the lead author of the study. "It would inhibit how much bone metastases they would have.”

Every year an estimated 1 million people develop metastases to the bones, particularly women with breast cancer. Drugs that inhibit RANKL may also help to alleviate the severe pain that metastases can trigger and improve the quality of life of patients.

Breast and prostate are among the most common cancers. More than a million new breast cancer cases occur worldwide each year, and half a million men are diagnosed with prostate cancer, according to the International Agency for Research on Cancer in Lyon, France. (Reuters)