Research Highlights from the 2019 San Antonio Breast Cancer Symposium, with Norah Lynn Henry, MD, PhD, FASCO

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 several studies presented at the 2019 San Antonio Breast Cancer Symposium, held December tenth through fourteenth in San Antonio, Texas. Dr. Henry is an Associate Professor in the University of Michigan's Division of Hematology/Oncology in the Department of Internal Medicine and is the Breast Oncology Disease Lead at the Rogel Cancer Center. View Dr. Henry’s disclosures at Cancer.Net. ASCO would like to thank Dr. Henry for discussing this research. Dr. Henry: Hello. I'm Dr. Lynn Henry from the Rogel Cancer Center at the University of Michigan. I would like to share with you a few of the research highlights related to breast cancer from the recent 2019 San Antonio Breast Cancer Symposium. I do not have any relationships to disclose related to these studies. Many of the exciting trials that were presented at this conference were for treatment of HER2-positive breast cancer. This is a specific type of breast cancer that accounts for about 1 in 5 breast cancers. Both of the studies I'm going to discuss related to HER2 involve treatment of patients with metastatic HER2-positive breast cancer or cancer that has spread beyond the breast and surrounding lymph nodes. The first trial is called HER2CLIMB. This is a phase III trial examining a new drug called tucatinib that is a pill that is designed to turn off HER2. Because of the type of drug that it is, it is thought to treat cancer both outside and inside of the brain which is important because many patients with this specific type of breast cancer can have the cancer spread to the brain. Patients who enrolled on this trial had previously been treated with multiple different treatments for HER2-positive metastatic breast cancer. In addition, almost half of the patients had metastases or cancer in their brain. In the HER2CLIMB trial, all enrolled patients were treated with the anti-HER2 antibody drug trastuzumab, also called Herceptin, as well as a chemotherapy drug called capecitebine or Xeloda. In addition, two-thirds received the new drug tucatinib and one-third received placebo. Overall, the drug combination was pretty well tolerated by patients with some diarrhea and fatigue. What is exciting about this trial is the patients who were treated with tucatinib had a longer time until their cancer progressed compared to those who took placebo. Those patients who had cancer in their brain got a similar benefit from the drug as those who didn't. In addition, on average, patients were also more likely to live longer if they took the tucatinib drug, an average of 4.5 months longer. This represents a potentially exciting new treatment option for patients with HER2-positive breast cancer. However, it has not yet been approved by the FDA. The second trial called DESTINY-Breast01 tested another new drug also for HER2-positive breast cancer. This drug is called trastuzumab deruxtecan which is a standard HER2 treatment trastuzumab with a chemotherapy drug attached to it. This was actually a phase II trial in which all patients got the same dose of this new drug in the data that they showed at the meeting. Everyone had been previously treated with a number of different drugs for HER2-positive metastatic breast cancer. In general, patients tolerated the treatment relatively well although some experienced lowered blood counts, hair loss, and inflammation of their lung. In this trial, almost two-thirds of the patient had at least partial shrinkage of their tumor and the average length of time that patients were able to continue taking the medicine was more than a year. This drug also represents a potentially exciting new treatment option for patients with HER2-positive metastatic breast cancer although it also has not yet been approved by the FDA. We are hoping that both of these drugs will get approved in the near future. Switching gears a bit, I will now mention a study that looked at a treatment for triple-negative breast cancer or cancer that is negative for estrogen receptor, progesterone receptor, and HER2 receptor. About 10% of all breast cancers are this type of cancer. A number of different trials have looked at using an oral chemotherapy drug called capecitabine beans or Xeloda for treatment of stage 1 to 3 triple-negative breast cancer. Studies have either looked at adding capecitabine to standard chemotherapy at the same time or using it as an additional treatment following completion of standard chemotherapy. However, to date, very few studies have shown that adding it is actually helpful. The investigators who presented their findings at the San Antonio meeting combined all the data from the trials that had been conducted so far, something called a meta-analysis. What they found was that specifically for the patients with triple-negative breast cancer, adding capecitabine to the treatment after the standard chemotherapy has been completed, decreased the likelihood of cancer returning and increase the overall survival of the patients. This was not the case for patients with other types of breast cancer including hormone receptor-positive and HER2-positive. In order to maximize the benefit for patients and minimize the toxic effects of treatment, not all patients with triple-negative breast cancer should take capecitabine. Rather, those who have a higher chance of their cancer returning such as patients who get upfront chemotherapy and still have cancer left at the time of surgery should talk with their oncologists about whether capecitabine is a good choice for them. One question that we cannot currently address is which patients are at higher risk for their cancer returning. In order to partially answer this question, a study was presented that examined compounds in the blood to see if they could be used to determine the likelihood of cancer returning in the future. Investigators looked at specific cancer compounds in the blood of patients who had been treated for stage 1 to 3 triple-negative breast cancer. Patients had blood samples drawn soon after surgery to look at both DNA from the cancer circulating in the blood, as well as cancer cells circulating in the blood. Those who had both DNA and cancer cells detectable in their blood were more likely to have their cancer return compared to those who didn't have either DNA or cancer cells in the blood. Those who had one but not the other were somewhere in between. Although we currently don't know how best to use this information when caring for our patients, and therefore this is unlikely to be something that your oncologists will order for you at this time, tests like this are likely to become commonplace in the future once we have more data. One final study I would like to mention is related to estrogen receptor-positive breast cancer. The NSABP B-42 clinical trial is addressing the question of how long postmenopausal women with hormone receptor-positive breast cancer should be treated with aromatase inhibitor therapy. The investigators compared 5 years versus 10 years. The trial was completed a while ago. And now that they have followed patients on trial for a full 10 years, the investigators have shown that taking the aromatase inhibitor letrozole for 10 years instead of 5, reduced the chance of having breast cancer return in the future. However, the benefit was relatively small. Therefore, since the benefit was relatively small and there is a risk of side effects from continuing to take the medicine, it is important for patients and oncologists to consider each patient's individual situation and risk of cancer returning when making the decision about how long she should take the medicine. In addition, there is more research going on that should provide additional information about how much benefit an individual patient is likely to get from this prolonged therapy. Overall, there is a lot of exciting research going on across all the different subsets of breast cancer. As you can see, the results of many important clinical trials were reported at the recent San Antonio Breast Cancer meeting and there are many more clinical trials ongoing that will hopefully result in the approval of multiple new effective treatments for breast cancer. In addition, there is research going on that is examining the impact of treatment on patients with breast cancer and trying to improve the lives of those living with breast cancer. Finally, there are even more trials going on trying to figure out how best to prevent breast cancer from occurring in the first place. Clinical trials are critical for the development of these new treatments. Well, that's it for this quick summary of this important research from the 2019 San Antonio Breast Cancer Symposium. 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 very much. ASCO: Thank you, Dr. Henry.  Learn more about breast cancer at www.cancer.net/breast. 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