Treating HER2+ Metastatic Breast Cancer: Caitlin’s Story - Episode 1

Classifying Breast Cancer

Sara A. Hurvitz, MD

Caitlin Flanagan

Sara A. Hurvitz, M.D., describes the subtypes, staging and grading of breast cancer.

Sara A. Hurvitz, M.D.: Hello and welcome to CURE® Expert Connections. I’m Dr. Sara Hurvitz, and I’d like to welcome one of my patients, Caitlin Flanagan, who’s here to share her story of her journey with HER2 [human epidermal growth factor receptor 2]-positive breast cancer. Welcome, Caitlin.

Caitlin Flanagan: Thanks for having me.

Sara A. Hurvitz, M.D.: I’m going to start off by talking a little about breast cancer, what it is, and what metastatic breast cancer is, and then we’re going to dive into Caitlin’s story.

Breast cancer is a compilation of many diseases. That’s the way I think about it. There are different subtypes of breast cancer. Currently, the way that we subdivide or classify breast cancers is based on the expression of receptors, hormone receptors such as estrogen receptor [ER] and progesterone receptor [PR], as well as another receptor called HER2, or human epidermal growth factor receptor 2. If a patient’s breast cancer lacks all three of those receptors, it’s commonly termed triple-negative breast cancer. The most common type of breast cancer is hormone receptor-positive, so ER+ or PR+, and HER2-negative. About 20%, maybe 25% at most, of breast cancer is classified as HER2+. HER2+ breast cancer is driven by amplification, or too many copies, of the HER2 gene, which leads to too much expression of the HER2 protein on the cell surface. This causes the cell to behave in a more aggressive fashion.

Thankfully, there are a number of therapies that have been developed against HER2 that are HER2-targeted therapies, the first one being trastuzumab. Now we have seven or eight others that have been FDA approved and are available to patients who have this subtype of breast cancer. Some HER2+ breast cancers also express hormone receptors. We have agents that target the estrogen receptor pathway that can be used to treat this.

Another way to look at breast cancer is the stage of breast cancer when a person is diagnosed. Stage tells you how big the tumor is at the time it was diagnosed and how far it has spread. Stages 1, 2 and 3 breast cancer are all accepted as being curable. Treatments need to be given and surgery. Sometimes radiation needs to be utilized to give a woman the highest odds of having the cancer go away and not return. On the other hand, stage 4, or metastatic breast cancer, is not typically considered to be curable. However, it is highly treatable. I think that you’ll all appreciate that a lot as you hear Caitlin’s story today.

There are a number of tests that are done at the time a woman is diagnosed with breast cancer to determine what stage the cancer is. Imaging, such as mammogram, ultrasound, MRI, and sometimes other imaging studies, such as PET/CT [positron emission tomography/computed tomography] scans or bone scans, can be done to determine if the cancer is well outside the area of the breast. Tests are also done on the tumor to tell us what subtype the breast cancer is. The tumor is tested for ER, PR and HER2. It’s also looked at in terms of its grade or how it looks under the microscope. How much does it look like breast tissue? Is it relatively disfigured and aggressive looking, or does it appear to be slower growing?

Transcript edited for clarity.