DESTINY-Breast06 and A-BRAVE: Advances in Breast Cancer Research

ASCO Daily News

Dr. Allison Zibelli and Dr. Erika Hamilton discuss the results of the DESTINY-Breast06 trial in HR+, HER2-low and HER2-ultralow metastatic breast cancer and the A-BRAVE trial in early triple-negative breast cancer, the results of which were both presented at the 2024 ASCO Annual Meeting.

TRANSCRIPT

Dr. Allison Zibelli: Hello, I'm Dr. Allison Zibelli, your guest host of the ASCO Daily News Podcast. I'm an associate professor of medicine and breast medical oncologist at the Sidney Kimmel Cancer Center of Jefferson Health in Philadelphia. My guest today is Dr. Erika Hamilton, a medical oncologist and director of breast cancer research at the Sarah Cannon Research Institute. We'll be discussing the DESTINY-Breast06 trial, which showed a progression-free advantage with the antibody-drug conjugate trastuzumab deruxtecan (T-DXd) compared to chemotherapy in hormone receptor-positive HER2-low or HER2-ultralow metastatic breast cancer. We'll address the implications of this study for the community, including the importance of expanding pathology assessments to include all established subgroups with HER2 expression, and the promise of expanding eligibility for antibody-drug conjugates. We'll also highlight advances in triple-negative breast cancer, focusing on the A-BRAVE trial, the first study reporting data on an immune checkpoint inhibitor avelumab in patients with triple-negative breast cancer with invasive residual disease after neoadjuvant chemotherapy.

Our full disclosures are available in the transcript of this episode.

Erika, it's great to have you on the podcast today.

Dr. Erika Hamilton: Thanks so much, Allison. Happy to join.

Dr. Allison Zibelli: Antibody-drug conjugates are rapidly changing the treatment landscape in breast cancer. The data from the DESTINY-Breast06 trial suggests that trastuzumab deruxtecan may become a preferred first-line treatment option for most patients with HER2-low or HER2-ultralow metastatic breast cancer after progression on endocrine therapy. First, could you remind our listeners, what's the definition of HER2-ultralow and what were the findings of this trial?

Dr. Erika Hamilton: Yeah, those are fantastic questions. Ultralow really has never been talked about before. Ultralow is part of a subset of the IHC zeros. So it's those patients that have HER2-tumor staining that's less than 10% and incomplete but isn't absolutely zero. It's even below that +1 or +2 IHC that we have classified as HER2-low. Now, I think what's important to remember about D-B06, if you recall, D-B04 (DESTINY-Breast04) was our trial looking at HER2-low, is that D-B06 now included HER2-low as well as this HER2-ultralow category that you asked about. And it also moved trastuzumab deruxtecan up into the frontline. If you recall, D-B04 was after 1 line of cytotoxic therapy. So now this is really after exhausting endocrine therapy before patients have received other chemotherapy.

And what we saw was an improvement in progression-free survival that was pretty significant: 13.2 months versus 8.1 months, it was a hazard ratio of 0.62. And you can ask yourself, “well, was it mainly those HER2-low patients that kind of drove that benefit? What about the ultralow category?” And when we look at ultralow, it was no different: 13.2 months versus 8.3 months, hazard ratio, again, highly significant. So I think it's really encouraging data and gives us some information about using this drug earlier for our patients with hormone receptor-positive but HER2-negative disease.

Dr. Allison Zibelli: I thought this study was really interesting because it's a patient population that I find very difficult to treat, the hormone receptor-positive metastatic patient that's not responding to endocrine therapy anymore. But it's important to mention that T-DXd resulted in more serious toxicities compared to traditional chemotherapy in this study. So how do you choose which patients to offer this to?

Dr. Erika Hamilton: Yeah, those are both great points. So you're right, this is after endocrine therapy. And in fact, about 85% of these patients had received at least 2 prior lines of endocrine therapy. So I have some people kind of asking, “Well, if endocrine therapy really isn't benefiting everyone in the second-line setting post-CDK, should we just move to the ADCs?” And, no, probably we should really make sure that we're exhausting endocrine therapies for those patients that are going to benefit. And once we determine somebody has endocrine-resistant disease, that's when we would think about switching.

In terms of the side effects, I think you're right. It's mainly ILD that's probably the more serious side effect that we worry about a little bit with trastuzumab deruxtecan. The good news is, through multiple trials, we've gotten a little bit better at managing this. We've pretty much all but eliminated any fatal cases of ILD, definitely less than 1% now. ILD rates, depending on what study you look for, kind of ranges in that 10% to 15% range. Any grade ILD on D-B06 was 11.3%. So really kind of making sure that we look for ILD at scans, making sure that patients are educated to tell us about any new pulmonary symptoms: cough, exertional dyspnea, shortness of breath at rest, etc. But I think the most common side effects that we really deal with on a daily basis with trastuzumab deruxtecan, luckily, is nausea, which we've gotten better at managing with the 2- or 3-drug antiemetic regimen, and probably a little bit of fatigue as well.

Dr. Allison Zibelli: Thank you. So, I think for most people in the community, the sticking point here will be expanding pathology assessments to include all of the subgroups, including the ultralow. Most patients in the community are not testing for HER2-low and HER2-ultralow now.

Dr. Erika Hamilton: Historically, we kind of all did HER2 IHC, right? And then as FISH became available, there were a lot of institutions that moved to FISH and maybe didn't have IHC anymore. And now, at least in my institution, we do both. But I think it's a very important point that you made that IHC was really designed to pick out those patients that have HER2-high, the 3 pluses or the FISH amplified cases. It was not to tell the difference between a 1+ or a 2+ or a 0 that's not quite a 0 and a 1+. So I think you're right. I think this is tough. I probably have a little bit more of an interesting take on this than some people will. But data from ASCO, not this year but in 2023, there was actually a pretty eloquent study presented where they looked at serial biopsies in patients, and essentially, if you got up to 4 or 5 biopsies, you were guaranteed to have a HER2-low result. Now, this didn't even include ultralow, which is even easier. If we know we include ultralow, we're really talking about probably 85% to 90% of our patients now that have some HER2 expression. But if we biopsy enough, we're guaranteed to get a HER2 low.

And so I think the question really is, if we know IHC wasn't really designed to pick out these ultralows, and we know kind of greater than 90% of patients are going to have some expression, did we kind of develop this drug a little bit backwards? Because we thought we understood HER2, and the reality is this drug is a little bit more like a sacituzumab govitecan, where we don't test for the TROP2. Should we really be kind of serial biopsying these patients or should maybe most patients have access to at least trying this drug?

Dr. Allison Zibelli: So I don't think that most of my patients will really be happy to sign up for serial biopsies.

Dr. Erika Hamilton: Agreed.

Dr. Allison Zibelli: Do we have any emerging technologies for detecting low levels of HER2? You talked about how the IHC test isn't really designed to detect low levels of HER2. Do you think newer detection techniques such as immunofluorescence will make a difference, or will we have liquid biopsy testing for this?

Dr. Erika Hamilton: Yeah, I think liquid biopsy may be a little bit hard, just because some of those circulating tumor cells are more of a mesenchymal-type phenotype and don't necessarily express all of the same receptors. Normally, if they're cytokeratin-positive, they do, but certainly there is a lot out there looking at more sensitive measures. You mentioned immunofluorescence, there are some even more quantitative measures looking at lower levels of HER2. I definitely think there will be. I guess, ultimately, with even the IHC zeros that are the less than 10% incomplete staining, having a PFS that was absolutely no different than the HER2 low, I guess the question is, how low can we really go? We know that even the IHC zeros doesn't mean that there's no HER2 expression on the cell surface. It just means that maybe there's a couple of thousand as opposed to 10,000 or 100,000 copies of HER2. And so it really appears that perhaps this drug really is wedded to having a lot of HER2 expression. So ultimately, I wonder how much we're going to have to use those tests, especially with what we know about tumor heterogeneity. We know that if we biopsy 1 lesion in the liver, biopsy a lymph node, or even another lesion in the liver, that the HER2 results can have some heterogeneity. And so ultimately, my guess is that most people have some HER2 expression on their breast cancer cells.

Dr. Allison Zibelli: So maybe we're going to be using this for everybody in the future.

Dr. Erika Hamilton: It certainly seems like we keep peeling back the onion and including more and more patients into the category that are eligible to receive this. I agree.

Dr. Allison Zibelli: Let's move on to triple-negative breast cancer, namely the A-BRAVE trial. This was an interesting trial for patients that did not get neoadjuvant immunotherapy and testing 2 groups. The first group was those with residual disease after neoadjuvant conventional chemotherapy. The second group was people with high-risk disease identified upfront that had upfront surgery. The study found that adjuvant avelumab did not improve disease-free survival versus observation, which was the study's primary endpoint. But interestingly, there was a significant improvement in 3-year overall survival and distant disease-free survival. Can you give us your thoughts on that?

Dr. Erika Hamilton: Yeah, I think this study was really interesting. Right now, the standard for our patients with larger or node-positive triple-negative cancers is KEYNOTE-522. It's a pretty tough regimen. It's kind of 2 sequential uses of 2 chemotherapies, so 4 chemotherapy agents total with pembrolizumab. But you're right, this study looked at those that had residual disease after neoadjuvant that didn't include immunotherapy, or those patients that didn't get neoadjuvant therapy, went to surgery, and then were receiving chemotherapy on the back end. I'm going to give you the numbers, because you're right. The 3-year disease-free survival rates were not statistically significant. It was 68.3% among those that had avelumab, 63.2% with those that had observation only. So the difference was 5.1% in favor of avelumab, but it wasn't statistically significant. A p value of 0.1, essentially. But when we looked at the 3-year overall survival rates, we saw the same pattern, those patients with the avelumab doing better, but it was 84.8% overall survival and not, unfortunately, dying, versus 76.3%. So the magnitude of benefit there was 8.5%, so about 3% higher than we saw for disease-free survival, and this was statistically significant.

So is this going to change practice for most patients? I probably don't think so. I think for our patients that have larger tumors that's recognized upfront or have node positivity, we're probably going to want to use neoadjuvant chemo. Being able to get a PCR is very prognostic for our patients and enables us to offer things on the back end, such as PARP inhibitors or further chemotherapy of a different type of chemotherapy. But for our patients that go to surgery and maybe the extent of their disease just isn't recognized initially, this could be an option.

Dr. Allison Zibelli: I agree. I think this will be a really useful regimen for patients where we get the surprise lymph node that we weren't expecting, or somebody who comes to us, maybe without seeing the medical oncologist, who got upfront surgery. So I thought this was really interesting. What kind of translational studies do you think we're going to do to try and understand which patients would benefit from avelumab?

Dr. Erika Hamilton: Yeah, I think that's a great question, and honestly, it's a question that we haven't really answered in the neoadjuvant setting either. Immunotherapy in breast cancer is just a little bit different than it is in some other diseases. We have a benefit for those patients that are PD-L1 positive in the first line. We really haven't seen benefit for metastatic outside of first line. And then in neoadjuvant, it was among all comers. We don't have to test for PD-L1. And now we have this avelumab data from A-BRAVE. I think the question is, is there’s probably a subset of patients that are really getting benefit and a subset that aren't. And I don't know that PD-L1 testing is the right test. We know a lot of people are looking at TILs, so kind of lymphocytes that are infiltrating the tumor, a variety of other kind of immunologic markers. But my guess is that eventually we're going to get smart enough to tease out who actually needs the immunotherapy versus who isn't going to benefit. But we're not quite there yet.

Dr. Allison Zibelli: Thank you, Erika, for sharing your valuable insights with us on the ASCO Daily News Podcast today.

Dr. Erika Hamilton: Thanks so much for having me.

Dr. Allison Zibelli: And thank you to our listeners for joining us. You'll find the links to all the abstracts discussed today in the transcript of this episode. Finally, if you like this podcast and you value our insights, please take a moment to rate, review, and subscribe wherever you get your podcasts. It really helps other people to find us. So thank you very much for listening today.

Disclaimer:

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. Guest statements on the podcast do not express the opinions of ASCO. The mention of any product, service, organization, activity, or therapy should not be construed as an ASCO endorsement.

Find out more about today’s speakers:

Dr. Allison Zibelli

Dr. Erika Hamilton

@ErikaHamilton9

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Disclosures:

Dr. Allison Zibelli:

None Disclosed

Dr. Erika Hamilton:

Consulting or Advisory Role (Inst): Pfizer, Genentech/Roche, Lilly, Daiichi Sankyo, Mersana, AstraZeneca, Novartis, Ellipses Pharma, Olema Pharmaceuticals, Stemline Therapeutics, Tubulis, Verascity Science, Theratechnologies, Accutar Biotechnology, Entos, Fosun Pharma, Gilead Sciences, Jazz Pharmaceuticals, Medical Pharma Services, Hosun Pharma, Zentalis Pharmaceuticals, Jefferies, Tempus Labs, Arvinas, Circle Pharma, Janssen, Johnson and Johnson

Research Funding (Inst): AstraZeneca, Hutchison MediPharma, OncoMed, MedImmune, Stem CentRx, Genentech/Roche, Curis, Verastem, Zymeworks, Syndax, Lycera, Rgenix, Novartis, Millenium, TapImmune, Inc., Lilly, Pfizer, Lilly, Pfizer, Tesaro, Boehringer Ingelheim, H3 Biomedicine, Radius Health, Acerta Pharma, Macrogenics, Abbvie, Immunomedics, Fujifilm, eFFECTOR Therapeutics, Merus, Nucana, Regeneron, Leap Therapeutics, Taiho Pharmaceuticals, EMD Serono, Daiichi Sankyo, ArQule, Syros Pharmaceuticals, Clovis Oncology, CytomX Therapeutics, InventisBio, Deciphera, Sermonix Pharmaceuticals, Zenith Epigentics, Arvinas, Harpoon, Black Diamond, Orinove, Molecular Templates, Seattle Genetics, Compugen, GI Therapeutics, Karyopharm Therapeutics, Dana-Farber Cancer Hospital, Shattuck Labs, PharmaMar, Olema Pharmaceuticals, Immunogen, Plexxikon, Amgen, Akesobio Australia, ADC Therapeutics, AtlasMedx, Aravive, Ellipses Pharma, Incyte, MabSpace Biosciences, ORIC Pharmaceuticals, Pieris Pharmaceuticals, Pieris Pharmaceuticals, Pionyr, Repetoire Immune Medicines, Treadwell Therapeutics, Accutar Biotech, Artios, Bliss Biopharmaceutical, Cascadian Therapeutics, Dantari, Duality Biologics, Elucida Oncology, Infinity Pharmaceuticals, Relay Therapeutics, Tolmar, Torque, BeiGene, Context Therapeutics, K-Group Beta, Kind Pharmaceuticals, Loxo Oncology, Oncothyreon, Orum Therapeutics, Prelude Therapeutics, Profound Bio, Cullinan Oncology, Bristol-Myers Squib, Eisai, Fochon Pharmaceuticals, Gilead Sciences, Inspirna, Myriad Genetics, Silverback Therapeutics, Stemline Therapeutics