Some Estrogen-Receptor-Negative Breast Cancers Become Estrogen-Receptor-Positive After Herceptin Treatment

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A study found that some HER2-positive, estrogen-receptor-negative breast cancer cells became estrogen-receptor-positive after being exposed to the targeted therapy Herceptin (chemical name: trastuzumab). This study was done on groups of cells in a lab, not in people.

While the results are very promising, more research is needed so doctors can better understand exactly how Herceptin affects the hormonal status of some breast cancers.

A healthy breast cell has estrogen receptors on its surface. These receptors act like antennae that receive signals from the hormone estrogen. Many breast cancers also have estrogen receptors on the surface of their cells. When breast cancer cells have hormone receptors, estrogen helps the cancer grow and spread. Hormonal therapy medicines reduce the risk of hormone-receptor-positive breast cancer coming back by blocking estrogen's effect or reducing the amount of estrogen produced in the body. Tamoxifen, the aromatase inhibitors, and Femara (chemical name: letrozole) are all hormonal therapy medicines.

Some breast cancer cells don't have hormone receptors or may stop making hormone receptors as time passes and the cancer progresses. About 25% of breast cancers are hormone-receptor-negative. Hormonal therapy medicines don't work on hormone-receptor-negative breast cancers.

Herceptin is used to treat HER2-positive breast cancers, regardless of the cancer's hormone-receptor status. Herceptin wasn't thought of as a treatment that could affect hormone-receptor status. But in the lab, this study showed that exposing HER2-positive, estrogen-receptor-negative breast cancer cells to Herceptin made some of the cancer cells start making estrogen receptors again (called upregulation). The study also found that the growth of the cancer cells that became estrogen-receptor-positive was slowed when the cells were then exposed to a hormonal therapy medicine. The researchers aren't sure how Herceptin causes estrogen-receptor-negative breast cancer cells to become estrogen-receptor-positive.

It's important to remember that this study was done with cancer cells in a lab, not in people. Still, the results suggest that Herceptin could make some breast cancers change from hormone-receptor-negative to hormone-receptor-positive and be able to be treated with hormonal therapy. Other research also suggests this can happen. A small study done in Italy found that 3 of 10 women diagnosed with HER2-positive, estrogen-receptor-negative, advanced-stage breast cancer had the cancer's hormonal status switch to estrogen-receptor-positive after being treated with Herceptin. Two of these women were then successfully treated with the hormonal therapy Femara. An ongoing U.S. study is looking at how Herceptin affects breast cancer hormone-receptor status.

Stay tuned to for the latest information about research on possible new breast cancer treatments.

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