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New Breast Cancer Gene Could Prove Usesful in Treating Patients

By David Brown
The Washington Post

Recent experiments with the "breast cancer gene" discovered 18 months ago suggest that the normal version of the gene may theoretically be useful as a treatment for the disease.

The gene, named BRCA1, produces a protein that slows both the formation and growth of breast tumors in laboratory animals. Equally important, the protein appears to do its work outside, rather than inside, cancer cells - a fact that greatly enhances its potential usefulness as a drug.

Abnormal versions of BRCA1 originally were found in families containing large numbers of women with breast cancer and, less frequently, ovarian cancer. Although these women account for only 3 percent of the 184,000 new cases of breast cancer diagnosed each year, researchers hoped that studying them would shed light on the far more common "non-familial" form of the disease.

The researchers found a protein that appears to be BRCA1 attached to membranes in breast cells - the site where secreted proteins are found. They collected it from fluid bathing breast cells grown in culture. Using an electron microscope, they even photographed a cell in the act of releasing several "labeled" molecules of the protein.

All three findings strongly suggested the BRCA1 protein, while manufactured inside the cell, does its work outside it.

Then the researchers looked for what that work might be. They injected a virus carrying the BRCA1 gene into mice with breast tumors. Some of the injected genes were taken up by the cancer cells, restoring the BRCA1 function that the cells had lost. Mice getting such treatments survived three times longer than animals that hadn't gotten them.

In a similar study, cancer-prone mice were injected with cancer cells, and some also with the BRCA1-carrying virus. Those getting the BRCA1 treatment developed tumors much more slowly than those that hadn't gotten it.

Together, the experiments suggest that the BRCA1 protein suppresses tumor growth - although it doesn't destroy tumors and may not prevent them completely. And it somehow does this outside the cell.