Q. I’ve been diagnosed with HER2-positive stage II breast cancer, and after surgery will be doing chemo (AC + T). After that’s done, my oncologist says I’ll be taking Herceptin. He called it a “targeted therapy.” What does that mean? Is it like tamoxifen?
A. Unlike tamoxifen, or the various aromatase inhibitors (Arimidex, Aromasin, Femara), Herceptin (trastuzumab) is NOT a hormone therapy drug. Instead, it’s called a targeted therapy (or immune targeted therapy). Targeted therapies are manufactured antibodies that “target” specific properties of cancer cells: their production of protein, their use of enzymes, or their ability to form new blood vessels to support growth. They leave healthy cells alone, which is a plus.
Q. Can we backtrack a minute? What’s HER2-positive mean, anyway?
A. Cells do three things: they grow, they rest, and they repair themselves. Genes inside the chromosomes in your cells regulate their activity, telling them when to grow, and when to stop growing and rest. If the genes malfunction, the patterns of growth/rest/repair are disrupted.
In HER2-positive breast cancer, there’s an excess of HER2 genes in the chromosomes of some of your cells. These genes tell the cells to grow extra protein receptors on their surface. With these extra receptors, the cells keep getting signals to grow, rather than to rest or repair. They grow much faster than the cells around them; this wild, uncontrolled growth turns them into cancer cells. Twenty-five percent of all breast cancers are HER2-positive.
Q. So, what does Herceptin do, specifically?
A. Herceptin is an antibody that blocks the HER2 protein from attaching itself to cancer cells, preventing them from growing. Herceptin works like tamoxifen, in a way: where tamoxifen attaches itself to a cell’s estrogen receptors, thus depriving the cell of the estrogen it needs to grow, Herceptin attaches itself to the cell’s protein receptors, effectively blocking the “grow” message. Herceptin can also signal your body’s immune system to destroy the cell to which it’s attached itself, so it carries a double punch. Like tamoxifen and aromatase inhibitors, Herceptin works to prevent recurrence in women whose HER2-positive cancer hasn’t metatastized.
Q. How will I take Herceptin? Is it a pill?
A. Herceptin is given intravenously, which means you'll get it in shot form. The first injection takes about 90 minutes; after that, weekly injections take about 30 minutes each. The duration of treatment depends on your specific pathology. Also, studies are currently underway examining whether Herceptin is just as effective given every 3 weeks, rather than weekly; stay tuned for updates from your oncologist.
FYI, Herceptin is also sometimes prescribed for women with large HER2-positive tumors, to shrink them before surgery. And it's often prescribed for women with HER2-positive metastatic breast cancer, where it's given indefinitely, or until the woman's doctor believes it's stopped working. It is typically given in combination with other chemotherapy such as a taxane, gemcitabine, navelbine, or other agents.