Male Hormones Drive Some Female Breast Cancers

Most breast cancers are fueled by the female hormone estrogen. In an interesting twist, scientists have discovered that a male hormone ignites breast tumor growth in some women.

Androgen, a hormone found in males, gives the marching orders for some breast cancer cells to kick into high growth gear. That's what scientists at Dana-Farber Cancer Institute have discovered in a new study.

HER2-positive and ER- breast cancers may soon have new therapies.

These findings will provide new targets for drug therapies in patients who don't respond to other hormone-blocking medications including tamoxifen.

The study's senior author, Myles Brown, M.D., says that not only has his team identified a new type of breast cancer that is driven by androgen and not estrogen, but they've found ways to block this mechanism or pathway.

Dr. Brown says these findings open the doors for women who don't respond to standard therapies.

Estrogen receptor-positive or ER+ is the most common type of breast cancer, found in 70-75 percent of cases. Estrogen makes cancer cells grow and spread. Tamoxifen and other estrogen-blocking drugs known as aromatase inhibitors, such as Femara (letrozole), keep the hormone from doing its deadly work.

The rest of breast cancers are called ER-negative because they don't have the estrogen receptors and don't respond to these medications.

Scientists know that even ER+ breast tumors have androgen receptors, though it's not understood how this hormone behaves in these cancers. Researchers think the androgen may boost the growth of cells that have the receptors for androgen but lack receptors for estrogen.

In this study, researchers found that five to 10 percent of breast cancers have receptors for androgen, but not estrogen. These patients also have too much of a protein called HER2 that divides rapidly when exposed to the male hormone, androgen.

Researchers uncovered the pathways, or how growth signals are transmitted. They found two proteins - WNT and HER2 - play key roles in this process.

Dr. Brown says that combination therapies that shut down these proteins or block the androgen receptor can be "effective anti-tumor agents" for women with this type of breast cancer.

The study was published the journal Cancer Cell.