Cancer involves the abnormal proliferation of cells. Around 90% of cancer deaths occur due to cancer spread. A recent study from City of Hope researchers found 40% of all women with HER-2-positive breast cancer are capable of developing brain metastasis.
Breast cancer patients die mostly due to the disease's spread into the brain and not because of its recurrence in the breast.
Breast cancer cells wrap themselves in reelin -- a protein typically found only in the brain -- that allows the cells to disguise themselves as "friend and not foe," avoiding a system in the brain designed to detect enemy cells. From these disguised cells, new deadly brain tumors form.
After performing brain surgery, Jandial and his team took leftover tissue samples and compared them to breast cancer tissue removed from mastectomies in the same women. They compared the expression of proteins and found that reelin expression was low in primary breast cancer tissue. However, its expression was significantly higher in HER2-positive breast cancer metastasizing to the brain.
"The cells are essentially able to act as spies that look like citizens," said Jandial. "They release a mesh of protein and escape the brain's natural defense weapons, causing tumors to grow in the brain."
Understanding these mechanisms is an important step in developing new therapies to treat brain cancers -- especially for metastatic cancers. Metastases are responsible for 90 percent of all cancer deaths, and patients diagnosed with brain metastases only have a 20 percent chance of surviving a year after diagnosis.