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ASCO: You’re listening to a podcast from Cancer.Net. This cancer information website is produced by the American Society of Clinical Oncology, known as ASCO, the world’s leading professional organization for doctors who care for people with cancer.

The purpose of this podcast is to educate and to inform. This is not a substitute for professional medical care and is not intended for use in the diagnosis or treatment of individual conditions. Guests on this podcast express their own opinions, experience, and conclusions. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement. Cancer research discussed in this podcast is ongoing, so the data described here may change as research progresses.

In this podcast, Cancer.Net Associate Editor Dr. Norah Lynn Henry discusses new research that was presented at the 2018 San Antonio Breast Cancer Symposium, held December fourth through eight in San Antonio, Texas. Dr. Henry is an Associate Professor in the University of Utah's Division of Oncology in the Department of Medicine, and Leader of the Women’s Cancers Disease Center at the Huntsman Cancer Institute.

ASCO would like to thank Dr. Henry for discussing this topic.

Dr. Henry: Good morning. I am Dr. Lynn Henry, a breast medical oncologist at Huntsman Cancer Institute in Salt Lake City. I would like to share with you one of the exciting breast cancer advances from the 2018 San Antonio Breast Cancer Symposium that was recently held in San Antonio, Texas. First, just a reminder that breast cancer is divided into 3 main categories determined by the presence or absence of receptors on the cancer cell. These categories include hormone receptor positive, HER2-positive, and the so-called triple-negative breast cancer, when all 3 of those main receptors are negative.

The study I'm highlighting, which is called KATHERINE, focused specifically on patients with HER2-positive breast cancer. The most commonly used antibody medication used to treat HER2-positive cancer is called trastuzumab, which is also called Herceptin. In the KATHERINE trial, the researchers were testing a different but related drug called trastuzumab emtanzine, which is also called Kadcyla. This new drug is the trastuzumab antibody linked directly to a type of chemotherapy drug. This allows the chemotherapy to be directed specifically to the HER2-positive cancer cells, so it generally causes fewer side effects than typical chemotherapy. Since the generic names of the medications are quite similar, I'm going to refer to them as Herceptin and Kadcyla in the rest of this podcast.

Many patients with HER2-positive breast cancer have treatment with chemotherapy and anti-HER2 drugs, like Herceptin, before they undergo surgery in order to try to shrink the cancer and ideally make it all go away. About half of the patients treated this way have no cancer found in their breast or lymph node when they have surgery, but the other half still have cancer remaining. Regardless of what is found at surgery, all patients are usually recommended to have additional treatment with Herceptin after surgery, so they receive a total of 1 year of Herceptin treatment. The KATHERINE trial is important because it asks the question, "Do women who still have cancer left in the breast when they have surgery after chemotherapy and anti-HER2 therapy—do they get more benefit from treatment with Kadcyla, which is Herceptin with the chemotherapy drug, for about 10 months after surgery compared to the standard treatment Herceptin?"

In this trial of almost 1500 patients, those who were treated with Kadcyla were much less likely to have their cancer return compared to those treated with Herceptin. The new treatment decreased the risk of cancer returning by about half. Patients with both hormone receptor-positive and hormone receptor-negative breast cancer appeared to benefit from this treatment, however, the downside was that patients treated with Kadcyla had more side effects and were more likely to have to stop the medication because of those side effects. We don't have any information yet about whether or not this new medication will allow patients to live longer following their breast cancer diagnosis, but we do know that it means they're less likely to have their cancers coming back.

So how do these findings change treatment recommendations? Before these data were available, oncologists were recommending Herceptin to all patients following surgery. Now, it is likely that once this new medication is approved to be used for this purpose, oncologists will recommend treatment with Kadcyla to those patients who still have cancer remaining at the time of surgery. In terms of what to expect going forward, there are many other trials ongoing to determine how best to treat patients with HER2-positive breast cancer in order to decrease the likelihood of cancer recurrence as much as possible, while also avoiding overtreating those who don't need as much therapy.

Well, that's it for this quick summary of this important trial from San Antonio 2018. Overall, we continue on a fast track in breast cancer with many new and exciting therapies being actively studied and research helping support our patients do better than ever before. Stay tuned to Cancer.Net for future updates from upcoming breast cancer conferences. Thank you.

ASCO: Thank you, Dr. Henry.  Learn more about breast cancer at www.cancer.net/breast. And if this podcast was useful, please take a minute to subscribe, rate, and review the show on Apple Podcasts or Google Play.

Cancer.Net is supported by ASCO’s Conquer Cancer Foundation, which funds breakthrough research for every type of cancer, helping patients everywhere. To help fund Cancer.Net and programs like it, donate at conquer.org/support.

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