Dr. Allison Zibelli and Dr. Megan Kruse discuss the potential benefit of endocrine therapy in ER-low breast cancer; the efficacy and tolerability of triplet therapy in PIK3CA-mutated, HER2-negative locally advanced or metastatic breast cancer; and more key research that will be featured 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 today. I am an associate professor of medicine and a breast medical oncologist at the Sidney Kimmel Cancer Center of Jefferson Health in Philadelphia. My guest today is Dr. Megan Kruse, a breast medical oncologist and director of breast cancer research at the Cleveland Clinic Taussig Cancer Institute. We'll be discussing key abstracts in breast cancer that will be featured at the 2024 ASCO Annual Meeting.

Our full disclosures are available in the transcript of this episode, and disclosures related to all episodes of the podcast are available at asco.org/DNpod.

Megan, it's great to have you back on the podcast.

Dr. Megan Kruse: Thanks, Alison. Happy to be here.

Dr. Allison Zibelli: So, let's begin with Abstract 505. This was another analysis of the SWOG S1007 (RxPONDER) trial, which was the trial that was looking at premenopausal women with intermediate risk oncotype scores. And do they benefit from chemotherapy? If you analyze the whole group, they do benefit from chemotherapy, but what this study questions is whether we can pull out the subset of these patients that actually benefit from chemotherapy? And what they tried doing was measuring various endocrine reproductive hormones and found that anti-mullerian hormone over 10 was the only one that predicted for chemotherapy benefit. What are your key takeaways from this study? Will it help us figure out who is truly postmenopausal biochemically?

Dr. Megan Kruse: I think this is really promising. This is one of the toughest situations in clinic, honestly, when you have a premenopausal woman who has an intermediate oncotype risk. We know that chemotherapy is not going to make a huge difference potentially in their breast cancer outcomes, but it may add to some small differential benefit. I think that many of our patients are really afraid about leaving any impactful therapy on the table. And so, it'd be nice to have another marker to help sort out who in this group will really benefit. And the AMH levels, I think, are something that are very accessible for most practices, easily orderable. And it seems like this cutoff of 10 is a very well-known cut point in the AMH interpretation, and a pretty clear-cut point. So, I think it gives a little bit more objective view of who may actually benefit or not.

When you look at the results shown in this abstract, for the women in the recurrence score less than 25 receiving chemotherapy followed by endocrine therapy, they had a benefit in five-year invasive disease-free survival of 7.8%. When you look at those oncotype reports and they suggest how much benefit you might get, that's right around the same number you see. So, I think that's supporting that this is the subgroup that's benefiting.

When you look at those patients with AMH less than 10, they actually had a negative 1.7% difference in overall survival. So, you wonder, are we harming these patients by giving them chemotherapy? I think that's too far of a stretch to say. I wouldn't be worried about harm. But hopefully, we can stop giving chemotherapy to patients who truly are not going to benefit if we have an additional biomarker of response. That's what the promise is for this.

So again, another potentially actionable abstract that we can put into practice pretty quickly. It's going to be hard to know how to use this, also in the context of the upcoming OFSET study or BR009, which is of course the study in the same group of premenopausal patients with node-negative or 1-3 lymph nodes involved, and intermediate oncotype scores, randomizing them to endocrine therapy with ovarian suppression versus chemoendocrine therapy. It would be kind of nice to see the AMH levels incorporated into that model to see if the same trend holds true. But I think we go back to the TAILORx and RxPONDER studies many times as good quality data, and the trend here is really striking.

Dr. Allison Zibelli: I really like this study because one of the things I often struggle with in the clinic as a practicing breast oncologist is who's really in menopause. And we end up having these fights with the gynecologists where sometimes our opinions differ. And it would be really nice to have something this clear cut to say, "You're in biochemical menopause or you're not." So, I look forward to seeing this used in a lot of different ways in the future.

Dr. Megan Kruse: Yeah, I agree. And I think it's based on the other markers we have with estrogen levels, with FSH levels. If you're checking those sequentially in patients, we know they go up and down, and it's really hard to tell what we are capturing at this single point in time. And maybe that's what we're seeing in this analysis is that the AMH is a little bit more stable and reliable marker. So, I really love that. And I don't know about you, but in clinical practice it can be really hard. A lot of our patients have had uterine ablations or hysterectomies but have intact ovaries. And so, figuring out ovarian function status is actually much, much harder than it may seem superficially.

Dr. Allison Zibelli: Okay, so let's focus on Abstract 513. I thought this was really interesting. It's a group of patients that we don't have much data for, and that's women that are ER-low, with an ER of 1% to 10% in early-stage breast cancer. Right now, national guidelines are sort of on the fence about whether these women benefit from endocrine therapy. So that's what this study tried to focus on. How will this study change how we approach this group of patients?

Dr. Megan Kruse: This study really gave me pause and made me rethink what I'm doing on a day-to-day basis, because here, what the authors found in a very large NCDB analysis was that for women with ER-low status, so ER 1% to 10% positive, they actually did have benefit receiving endocrine therapy, it seems. What they found, after you adjust for many other confounding factors like age, comorbidity, and PR status, is that patients with ER-low breast cancer when they did not receive endocrine therapy actually had worse overall survival outcomes with a hazard ratio of around 1.2 to 1.3.

This is a group where I have typically not pushed endocrine therapy very strongly. I think the patients, especially now, are receiving such intense therapy with chemoimmunotherapy in the preoperative setting, by the time they reach their adjuvant phase with immunotherapy, maybe with capecitabine, maybe with a PARP inhibitor, endocrine therapy seems, "Oh, why bother after we've done all of this?" And we know that the toxicities of endocrine therapy are real and can be very problematic. And so, I have often felt like it's the least important part of therapy and questioned whether we should even bother. But I think this analysis really challenges that and makes us think twice. And I think it speaks to a theme that we're seeing more and more about the heterogeneity of these breast cancer subtypes. And again, talking about clear-cut points in analysis, nothing is truly black and white. So maybe that little bit of expression does mean something.

It does kind of stand in contrast to what we see in studies of ER-low behaving a bit more triple-negative like, but maybe they're their own category, and maybe it gives us a place to look for other therapy synergy in the future. But it certainly will make me stop and think again when I see a ER 4% patient. Should I talk to them about endocrine therapy?

Dr. Allison Zibelli: Yeah, I totally agree with everything you said there. And we know that this is a biologically different group of patients than the ER strongly positive group, but maybe not as different as we once thought.

Dr. Megan Kruse: Yeah. And I think there's still a lot of unknowns here about what if they're ER truly negative and PR a little bit positive. So, these clinical situations don't come up that frequently, but when they do, they're humbling, because I think we really, as much data as we have in breast cancer, it's pretty limited for these types of patients.

Dr. Allison Zibelli: So, let's move on to Abstract 1003, which was a new combination in the INAVO120 trial. It was palbociclib plus fulvestrant with either inavolisib or placebo in patients with PIK3CA-mutated hormone receptor-positive, HER2-negative, locally advanced metastatic breast cancer in the second line, who relapsed within 12 months of adjuvant endocrine therapy completion. This is a big group of patients for us. Can you tell us about the study? And does this triple therapy, in your mind, represent a new standard of care?

Dr. Megan Kruse: Yeah, this study was initially presented at our 2023 San Antonio Breast Cancer Symposium, and there I felt like it was a little bit of a surprise. There's been so much talk about PI3K-AKT-PTEN pathway impactful drugs and targetable mutations. We've heard a lot about alpelisib and capivasertib, and how these drugs are fitting into our practice. Then all of a sudden, we have this data with inavolisib that I wasn't really expecting to see. And perhaps I think one of the reasons that this study came about so suddenly, seemingly, and so quickly is because it looks at a really high-risk patient population. And so, these are those patients that are having relapses of their breast cancer within their initial, while on adjuvant AI therapy or within 12 months of stopping. And so, having a marker of this patient group that is developing, I think, early endocrine resistance and it's another space where it's kind of hard to identify who these patients are upfront. And so their response to therapy tends to be one of the best markers of risk moving forward.

So, when this trial was originally presented, what was quite striking is that the progression-free survival was more than doubled for the triplet combination compared to the control arm. And those numbers were PFS of 15 months versus 7.3 months for the triplet versus the control. The response rate was also significantly improved, with the triplet going above 50%, versus a response rate in the control of about 25%. So, the results were really striking. But they clearly come with some caveats, which are that this is a very defined patient population of risk. Of course, they have to have the biomarker of a PIK3CA mutation, and in the control arm here, there was no PIK3-targeted medication. And so you wonder, are we just getting better results by including that more specific targeted therapy earlier on? It's hard to know, but I think that could certainly be a big part of this.

And the other caveat, when I'm looking at the data, is how might we think about this in our real population? Because as we know, drugs that impact this pathway tend to have a lot of toxicity concerns, primarily hyperglycemia, diarrhea, and rash. And with this particular agent, there was also notable stomatitis, which is something we've seen with everolimus, of course, in this pathway, but not maybe as much with alpelisib and capivasertib. When you're thinking about all of those toxicities, keep in mind that this trial population included patients with a pretty tight fasting blood sugar requirement, A1c of less than 8, and not requiring insulin. So all of that being said, I think this combination seems really intriguing for efficacy. This is a patient population I'm worried about, because we know that these patients are likely not going to get the same upfront benefit of CDK4/6 inhibitor-based therapy, like maybe we see for a patient with long disease-free survival or de novo metastatic breast cancer. But I think it's going to have some meaningful issues in clinic regarding tolerability. And then, of course, the regimen is more complex. We're talking about two different oral agents and an intramuscular injection, which could be hard for some patients, and it's going to have some decent financial toxicity associated with it.

So, I think it's really, really exciting and has the potential to make an impact in first-line therapy. But I don't envision it being the standard of care first-line therapy for everyone, particularly in light of some of the other data we have in the first line questioning, like from the SONIA trial, how important is CDK for everyone? Again, this is I think where we're starting to get subsets within subsets of this first-line patient population of who needs escalation of therapy and who may benefit from more de-intensified therapy.

Dr. Allison Zibelli: I agree, these agents have significant toxicity, and especially financial toxicity is something that we at the academic setting frequently forget about because a lot of our patients are on trials. So, it will be interesting to figure out how we're going to use these agents in real life.

So, for our final abstract, I wanted to discuss Abstract 10508, which was a prevention trial. I think pretty much everybody's patients are going to be asking them about this because it's about GLP-1 inhibitors. We know that bariatric surgery does prevent obesity-associated cancers. This study explored whether the GLP-1 agonists could offer a similar result to bariatric surgery in patients with BMIs over 35. What do you think about this study?

Dr. Megan Kruse: I thought this was such an interesting and timely study and question. These drugs are out there – Ozempic, Mounjaros, and Wegovy – and our patients ask about them. And I think there has been a lot of interest for years now about the impact of lifestyle factors on cancer incidence, particularly in breast cancer, where we know that obesity does seem to be related to cancer incidence. And with all of our concerns about hormonal exposure and extra weight, extra adipose tissue being a source of potential extra estrogen, this is a really key topic.

Talking about financial toxicity, again, I think that is honestly probably the bigger hurdle because this study does reinforce that patients who are receiving GLP-1 receptor antagonists and those who have had bariatric surgery do benefit in terms of cancer-related survival and all-cause related survival. So, I think the impact on metabolic factors is making a difference in cancer incidence and outcomes. But access and equity will be the big issue here, right?

Dr. Allison Zibelli: Yes.

Dr. Megan Kruse: Can we get patients on these drugs? I certainly have had patients with a history of breast cancer who have been on these medications, and they have done great with them in terms of weight loss. We know that our therapies, many times, do have the side effect of weight gain. So, I wonder if there is a part of weight management that maybe we haven't talked about so much as oncologists that we need to talk about moving forward and would be very welcome by our patients. But it'll have its own caveats, of course. Not only the financial issue but there's the durability issue. And I think when you look at the degree of impact of these medications versus bariatric surgery, you do see a greater impact from bariatric surgery, in not only the degree of weight loss but also the sustainability of that weight loss. So, I think for the right patient at the right time, bariatric surgery may still be the better option, but that's not going to be an option for a lot of patients. It is a huge shift in lifestyle and medications and many ways might be easier, so more to come.

I also wonder about looking at this data through the lens of different cancer types. What will we find out? Is the trend for colon cancer going to be different from the trend for breast cancer? Will the trend within breast cancer be different for breast cancer subtypes? I would very much welcome more data in this space, and it is nice to see a first step forward.

Dr. Allison Zibelli: I thought the most interesting thing about this study was that while bariatric surgery patients lost more weight, GLP-1 patients had a higher decrease in obesity-related cancer risk. So, it shows to me that there is something beyond just weight. It is something in metabolism that is driving these cancers.

Dr. Megan Kruse: Yes, and I think that that goes back to some things we have thought about for a long time with insulin levels and insulin-like growth factor, and all of these things that I think when our patients look at more metabolic approaches to cancer control, this is probably what we are trying to get at. We have just never had great ways to measure it or influence it, and perhaps now we finally do. I would love to see some partnering work here in the future with oncologists and endocrinologists and digging into these patients who have great responses to see what we are actually seeing at the hormone level.

Dr. Allison Zibelli: Well, thank you so much, Megan, for your great insights today on the ASCO Daily News Podcast. We really appreciate you coming to talk with us again.

Dr. Megan Kruse: Thank you. It has been a great conversation. Thank you for opening my eyes to these abstracts, and I am happy to see what else ASCO brings.

Dr. Allison Zibelli: And thank you to our listeners for joining us today. You will find links to all the abstracts we discussed today in the transcript of this episode. Finally, if you value the insights you hear on the ASCO Daily News Podcast, please take a moment to rate, review, and subscribe wherever you get your podcasts. It really helps other people find us. Thank you for listening.

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. The 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.

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Disclosures:

Dr. Allison Zibelli:

None Disclosed

Dr. Megan Kruse:

Consulting or Advisory Role: Novartis Oncology, Puma Biotechnology, Immunomedics, Eisai, Seattle Genetics, Lilly

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