The Effects of a Novel CDK for Six Inhibitor on Breast Cancer

Dr. Allison Zibelli and Dr. Megan Kruse highlight the PALMIRA and LEONARDA-1 trials, a new standard of care in the treatment of hand-foot syndrome for patients receiving capecitabine, and other key breast cancer studies that will be featured at the 2023 ASCO Annual Meeting.

TRANSCRIPT

Dr. Allison Zibelli: Hello. I'm Dr. Allison Zibelli, your host for the ASCO Daily News Podcast. I'm an assistant professor of medicine and a breast medical oncologist at the Sidney Kimmel Cancer Center at Jefferson Health. My guest today is Dr. Megan Kruse, a breast medical oncologist at the Cleveland Clinic Taussig Cancer Institute. We'll be discussing key abstracts in breast cancer that will be featured at the 2023 ASCO Annual Meeting.

Our full disclosures are available in the show notes and disclosures of all guests on the podcast can be found on our transcript at asco.org/DNpod.

Megan, it's great to speak with you today.

Dr. Megan Kruse: Thank you for having me.

Dr. Allison Zibelli: Let's begin with Abstract 1001. This is the PALMIRA trial, a study of second-line endocrine therapy plus palbociclib in HER2-negative ER-positive patients. We all have patients who have progressed on a CDK4/6 inhibitor, and this trial investigated a possible treatment approach for these patients. What are your thoughts?

Dr. Megan Kruse: I think this is a really tough space to know what to do, so I'm glad that we're getting more data to help inform our treatment decisions here. And I think it's also really tough for patients to wrap their heads around letting a CDK4/6 inhibitor go when many of them have done so well with it in the first-line treatment setting. So, in this study, patients were randomized to either continue on with their CDK4/6 inhibitor in the second line, the palbociclib specifically, along with a different endocrine therapy versus just switching to a different endocrine therapy alone. And what I thought was interesting was that the progression-free survival for both arms of the study were actually pretty similar. But that if you look at six-month progression-free survival as a particular endpoint, there were more encouraging results in the patients that continued on with the maintenance palbociclib along with the alternate endocrine therapy compared to what they received in the first line. So, I think this leaves the door open for certain patients to maintain ongoing benefit from their first-line CDK4/6 inhibitor with a switch in the endocrine therapy in the second line.

The challenging thing is it's hard to know who these patients are. I didn't see anything yet in the abstract that would suggest a differential population where this approach would be more successful. But the authors do note that there are some additional biomarker analyses that are pending. So, I hope that we see some data there when the full abstract is presented to get a sense of who might be a good candidate for this approach within the hormone receptor-positive HER2-negative metastatic breast cancer population.

Dr. Allison Zibelli: Thank you for that, Megan. I am not alone in finding these patients very hard to treat once they progress on a CDK4/6 inhibitor because there really is no standard of care in this space. So, I'm hoping this will provide some additional guidance for this patient population.

Dr. Megan Kruse: Yeah, I agree. Absolutely. I think the patients in the second line are now very different biologically after they've received CDK4/6 inhibitor. So, knowing what to do in this space really challenges our historical standards of care and I think it's a big gap in knowledge.

Dr. Allison Zibelli: Next, let's talk about Abstract 1007. This was a study about fixed-dose capecitabine and metastatic breast cancer. We all know that the package insert dose for capecitabine is probably too high, and a lot of us have been tinkering with the dose and scheduling in the absence of good evidence for that approach. This study looked at the efficacy of a lower dose with a fixed schedule. How do you think this will influence clinical practice?

Dr. Megan Kruse: Yeah, I was excited to see this study. I think that has pretty immediate ramifications for what we do. And particularly with respect to the fixed-dose of capecitabine that was chosen, the authors ended up going with 1,500 milligrams twice a day, which honestly, in my practice is sort of where I end up with a lot of my patients. Even if I try to start higher based on their body weight and based on the package insert dosing, I find that I pretty much end up at 1,500 milligrams twice a day no matter what I do. So, I thought that this was a very realistic study and happy to have it as part of our collective breast cancer knowledge. The other thing that was interesting here, not only the dose that they used but also the schedule that seven days on, seven days off I think is something that we do have data and a precedent for, although it doesn't seem to be utilized from the beginning. I find myself sticking with the 14 days on and seven days off when I start patients on capecitabine for metastatic disease management.

What was great in this study was that in terms of efficacy for cancer control, both dosing and schedules, either the fixed-dose or the standard dose seemed equivalent. So, that provides a lot of reassurance, I think, for us as providers, and we can share that easily with patients. But what was notable was that the incidence of diarrhea and hand-foot syndrome, mucositis as well, were all much, much better with the fixed-dose and that more limited seven days on, seven days off schedule. To me, that's very meaningful because I think we run into a lot of treatment delays and a lot of unnecessary modifications with our patients that we start on the higher dose, that maybe will have better dose intensity over time if we started with a lower dose and a schedule that is more feasible for patients and has a better impact on their quality of life. So, I think this was a great abstract, and I'm excited to see what happens with the utilization of capecitabine. It'll be nice to see some real-world data potentially, once this is out there, of what practitioners are actually doing.

Dr. Allison Zibelli: Well, I know that in my case, I'm immediately calling the builders of our EMR to put this into our treatment pathways. I think that capecitabine is underused in the community because of the perception that it has so many side effects and that's a shame because it really has a lot of activity and it's convenient for patients. So, I'm hoping this will allow oncologists to use this drug more in the second-line setting.

Dr. Megan Kruse: Yeah, I agree. I think it's a terrific option and it's that really nice bridge from the targeted endocrine approaches that we use for patients in the first line, potentially second line, then as they transition into needing chemotherapy and becoming endocrine resistant, having an oral option is really a nice bridge there and I'd love to see patients be able to stick with it longer than potentially some do, just based strictly on toxicity. So, I love having this data out there.

Dr. Allison Zibelli: So moving on to Abstract 12005. This is a related abstract because it's addressing a common toxicity in patients that are on capecitabine, which is hand-foot syndrome. This abstract described a randomized, double-blind, placebo-controlled trial of topical diclofenac to prevent hand-foot syndrome. Could you tell us more about this? And would you consider this to be a new standard of care?

Dr. Megan Kruse: I would consider this to be a new standard of care. I think that this abstract is exciting, number one because focusing on symptom management is something that we need more data on. I think we think so much about anti-cancer efficacy of our drugs, which of course is our first priority, but those drugs only have their benefit if we can get patients to take them. So focusing on symptom management is key and it's something that we don't see a ton of abstracts on many times at our national meetings.

And the other thing that I really like about this particular abstract is that the topical diclofenac is something that's so readily accessible. I would say that a lot of my patients have this in their medicine cabinets already because we're thinking about things like joint pain and arthritis all the time. So it's something that I think, again, is immediately actionable and it's hard to know exactly what we would do with this given the last Abstract we talked about where hopefully we're running into less hand-foot syndrome. But I see them as being very complementary pieces of data because there's no reason why we couldn't use both pieces of data together and use a more fixed-dose approach to our capecitabine prescriptions, but also use the topical diclofenac as another way to decrease the incidence of hand-foot syndrome.

I don't know about you, but hand-foot syndrome is the thing that I hear the most about with capecitabine. We're always educating on diarrhea and mucositis and blood counts and fatigue, but by far and away the day-to-day toxicity that I encounter that we manage or have to take time to think about is hand-foot syndrome. So knowing that the use of the topical diclofenac decreases the incidence of hand-foot syndrome in general and particularly higher grade and more problematic, hand-foot syndrome, I think is a big step forward. Our patients are always looking for things to add to their arsenal for symptom management. So we already have a list of moisturizing lotions we talk to them about, and I see us adding this line about the topical diclofenac in there right away in June.

Dr. Allison Zibelli: I agree with you. I think that there is not enough attention paid to the side effects of our therapies and I thought this was a great abstract.

Next, let's talk about the LEONARDA Trial. Abstract 1017. This trial assessed lerociclib, a novel CDK4/6 inhibitor, in ER-positive HER2-negative metastatic breast cancer. Could you describe this trial and how do you think that this fits into the treatment landscape?

Dr. Megan Kruse: So this trial, the LEONARDA Trial, uses lerociclib in combination with fulvestrant for patients with essentially second-line treatment of HR-positive HER2-negative breast cancer, and is randomized against fulvestrant in combination with placebo. And what we saw here I think is a pretty typical trend that we see for our endocrine therapy CDK4/6 inhibitor studies where there was roughly a doubling of progression-free survival. So the progression-free survival was 11 months with the lerociclib and fulvestrant combination compared to the placebo fulvestrant combination at 5.5 months. The response rates were also higher in the CDK4/6 fulvestrant arm compared to the fulvestrant placebo arm at 26.9% versus 9.9%.

What's interesting about this particular novel CDK4/6 inhibitor is that it's continuous dosing and it's BID dosing from what the abstract describes. And I think then that leads to a natural comparison with our other continuous BID dosing, CDK4/6 inhibitor, which is abemaciclib. And so when I was evaluating this abstract, I think the efficacy results were pretty much what I was expecting for a CDK4/6 inhibitor with endocrine therapy. What drew my attention was more the toxicity information. And so when you look at that, you actually see a pretty high rate of both neutropenia and leukopenia for this novel CDK4/6 inhibitor. Those were at 90% all-grade neutropenia and 87% all-grade leukopenia. And I think that's higher than what we would expect in comparison to abemaciclib. So if you look at the results for the MONARCH-2 trial, we're seeing all-grade neutropenia being about 50% with abemaciclib.

So when I'm thinking about how does this new drug fit into the landscape, you would think about patients who maybe have a preference for continuous dosing rather than cycled dosing like some of our other CDK4/6 inhibitors. But in that perspective, you'd be looking for some other sort of benefit, and I think when it comes to cytopenias, this might not actually fill that mark. It does seem to have a lower incidence though of diarrhea, so that is definitely a benefit. Here, we saw that all-grade diarrhea with the lerociclib was just under 20%, and the rate of that with abemaciclib in the MONARCH-2 trial was actually 87%. So if I'm looking for a combination of lesser diarrhea, continuous dosing, this might actually have a space. But I think it's hard to know what to do with the CDK4/6 inhibitors now that we have so many options. The selection of particular agents and the sequencing of those agents is still really a challenge. So as more drugs get added to the space, it just gets a little bit murkier about what we would choose.

Dr. Allison Zibelli: I agree. I'm not sure how I would fit this into my current therapeutic plan, so we'll be looking for more data about this in the future.

Dr. Megan Kruse: Agree.

Dr. Allison Zibelli: Finally, Abstract 517 looks at treatment outcomes for patients with very small node-negative HER2-positive tumors in the SEER database. I thought this was very interesting because we've had very limited data in this patient population. I recently had two patients in my clinic with these T1a and T1b HER2-positive tumors, and up until now, we really haven't had much guidance. So what can we learn from this data?

Dr. Megan Kruse: I agree with you. Clinically, this is a big challenge, and I think it is one of the challenges that comes about with having such excellent treatment options where we don't want to leave anything on the table for patients with potentially curable disease. And there's that specter of how aggressive HER2-positive disease left untreated or appropriately untreated is in our minds and what that could mean for patients' lives. And so I think our tendency for these types of patients is to treat more aggressively sometimes than we would need to in the absence of data. And knowing that many of our trials in this space have reflected patients with larger tumors or lymph node positivity really makes it challenging. So I was really encouraged to see these results, and it's a large study. So this is a study of almost 13,000 patients with stage I HER2-positive breast cancer, specifically T1N0 HER2-positive breast cancer. And as you might expect, most of these patients, about three-quarters, were also hormone receptor-positive.

So the authors did a really nice job at breaking down the breast cancer-specific survival results at three, five, and seven years over this time frame for patients and then dividing it out into the hormone receptor-positive HER2-positive and hormone receptor-negative HER2-positive. So I think the key points to take away from this are that overall, the breast cancer-specific survival for these patients is excellent. And I think that that is probably what we have come to expect with data that we've seen from the APT study and its longer-term follow-up. What was interesting to me about this was that the use of chemotherapy over the study period from 2010 to 2019 actually increased over time, and I would suspect that APT had a lot to do with that. Coming out in 2015 and suggesting that it was possible to treat these patients with smaller tumors in a way that hopefully was meaningful without overdoing it. I wasn't really surprised to see that trend.

I think the key takeaway point here is that for patients with T1c disease, those really seem to be the ones where we see a differential benefit between the group of patients that received chemotherapy and those that did not. For the T1a and T1b patients it seemed like breast cancer-specific survival at the different endpoints was quite similar and with really, really high numbers, I mean, between 98 and 100% survival. When you get to those T1c patients, that's where you're starting to see the numbers slip a bit. And with survivals that are about 4-5% different for the arm that received chemotherapy versus those that did not, in favor, of course, of the chemotherapy. The trend was actually more statistically significant for the hormone receptor-positive HER2-positive patients, which was unexpected in my mind. That might be more of a statistical change than anything because the magnitude of difference actually was a little bit stronger for the hormone receptor-negative HER2-positive patients.

But I think in general, what this reinforces for me is that those smallest of the small HER2-positive tumors probably don't need chemotherapy. And that's what's reflected in my institutional guidelines, and I think I will continue to practice that way. That's really for the T1aN0 patients. For the T1bN0 patients, those are patients that right now I am recommending chemotherapy for. And these results made me wonder if it's really necessary because the five-year breast cancer-specific survival was nearly identical in this study. So I'd love to have some more conversations with folks about that at ASCO and really think about what this means for our national guidelines. No surprise, I think the T1cN0 patients will continue to get chemotherapy, and that is appropriate in my mind based on this information.

Dr. Allison Zibelli: It's so nice to have data on something that's been a data-free zone for so long. So I was really happy to see this abstract.

So thank you, Megan, for coming on this podcast today and sharing your insights with us. We really appreciate it.

Dr. Megan Kruse: Thank you for having me. It definitely energizes me as we approach the upcoming ASCO meeting.

Dr. Allison Zibelli: And thank you to our listeners for joining us today. You'll find links to all the abstracts discussed today in the transcripts for this episode. Finally, if you value the thoughts and insights that you hear on the ASCO Daily News Podcast, please take a minute to rate, review, and subscribe. It helps other people to find us, and you can do that wherever you get your podcasts.

Disclaimer:

The purpose of this podcast is to educate and 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, experiences, 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