Dr. Sara Tolaney:
So welcome to The ASCO Post Roundtable Series on Evolving Paradigms in the Treatment of Hormone Receptor–Positive, HER2-Positive Metastatic Breast Cancer. My name is Sara Tolaney and I'm a breast medical oncologist at Dana-Farber Cancer Institute. And today joining me are two of my colleagues Dr. Mark Pegram and Dr. Ian Krop. So thank you so much for being here with us today.
Today, we're going to be discussing the treatment and management of metastatic hormone receptor–positive, HER2-positive breast cancer with three patient cases. And in our second installment we'll be discussing what to do after someone receives first-line induction therapy with a taxane and trastuzumab and pertuzumab for metastatic hormone receptor–positive, HER2-positive disease. So we'll dig into our second case.
This is a 62-year-old woman who had initiated therapy with the CLEOPATRA regimen. So she got weekly paclitaxel with trastuzumab and pertuzumab for her de novo metastatic hormone receptor–positive, HER2-positive breast cancer.
She initially had a liver metastasis and with the induction treatment did have significant reduction in that liver lesion. She also had reduction in her initial breast mass. And so after seven cycles of therapy she started to get a little bit of neuropathy. And so this is a question that arises is, what do you do in this case? Do you guys continue chemotherapy? How long do you continue it for? When do you stop it? And what should be the criteria that we keep in mind for figuring out what duration of that induction chemotherapy patient should receive? Maybe, Ian, I'll start with you. How do you think about this?
Dr. Ian Krop:
Yeah, so here's an area where we have clear data supporting the approach that was taken with this patient. But the specifics on when to stop the chemo, I think we don't have strong data and I think we really should be personalizing for the particular patient. And obviously and fortunately, patients with HER2-positive advanced disease now do very well and live for a long time in general. So we really have to be careful about toxicities that, particularly those that could be long-term, like neuropathy. So I keep that in mind and trying to minimize the chance that a patient's going to have persistent neuropathy.
And in terms of when to stop, in general, I think the two things are toxicity and whether you feel like clinically the patients maximize their response from the therapy. And this patient's had a complete clinical response in the liver. They've had a good reduction in their breast mass and they're having this neuropathy. I mean, I think it's a conversation you have. Certainly, you can try dose-reducing the paclitaxel, adding breaks if that hasn't already been done. But I would think that in this particular patient I would be pretty close to stopping, if not stopping right then, depending again on the conversation you have with the patient and then switching to a more maintenance approach.
Dr. Sara Tolaney:
No, thanks. Mark, do you have any rules of thumb for when you tend to stop the taxane therapy?
Dr. Mark Pegram:
Again, it's a cumulative dose limiting toxicity in the form of neuropathy. That's the top three reasons to stop the taxane component. In many cases, it depends on what the patient's profession is. If they're a concert violinist or a pianist or something like that, you can't tolerate anything above grade 1 neuropathy. And I think grade 2 neuropathy is unacceptable, to be honest with you. I think you need to stop right before grade 2 neuropathy. And again, as Ian said, dose modification, you should do liberally at the onset of neuropathy if you think you need a little bit more mileage out of the chemo backbone. But otherwise, if they've achieved the kind of maximum response and certainly if they've achieved a CR, I would be very content to switch to a maintenance therapy position with dual antibodies and endocrine therapy and now perhaps CDK4/6 inhibition to boot.
Dr. Sara Tolaney:
So that is exactly, I think, the question is, so what are you doing when you stop the taxane therapy? And maybe you could tell us a little bit about some of the new data that has emerged about maintenance strategies and some of the data that actually we just saw at San Antonio.
Dr. Mark Pegram:
Well, right now know, heretofore, we've been usually integrating endocrine therapy along with continuation of the dual antibodies after chemotherapy induction with dual antibodies in a CLEOPATRA-like regimen. That's been the current standard of care until this most recent San Antonio. But based on the strength of preclinical data from Shom Goel that showed really elegantly in a cancer cell paper, back in 2016, using transgenic mouse models, cell-based assays, and xenograft assays, that there's synergy between CDK4/6 inhibition and anti-HER2 therapy, both with antibodies and with small-molecule TKIs. Moreover, he showed a synergy with CDK4/6 inhibitors in that paper, importantly. That was the major outcome of his observation is that CDK cyclin, in particular cyclin D1 and CDK4 complexes, can cause resistance to HER2 target therapy, which can be overcome with CDK4/6 inhibitors, such as abemaciclib, in the paper that he published.
Moreover, Neil O'Brien later showed similar arguments with cell-based and xenograft assays combining CDK4/6 inhibition with HER2-targeted therapies. Moreover, he showed that, in some of the original cell line panels looking at screens of CDK4/6 inhibitors, some of the responding cell lines were in fact hormone receptor–positive and HER2-positive.
Then based on the strength of those preclinical studies, your paper on the monarcHER trial in previously treated HER2-positive metastatic disease, really convincingly showed that this combination of fulvestrant and abemaciclib and HER2-targeted therapy is effective, even in previously treated metastatic patients. And so that set the stage for follow-on studies such as the study that was presented last year at ASCO, the PATRICIA study, a randomized phase II study, showing the same kind of observations that CDK4/6 inhibition plus integral therapy plus trastuzumab vs a standard of care control arm was a positive randomized phase II trial. And that set the stage for this pivotal phase III PATINA trial, which is a randomized phase III trial involving over 500 patients, HER2-positive, hormone receptor–positive patients after they finished the chemo/trastuzumab/pertuzumab first-line induction therapy, they were randomized to maintenance with either trastuzumab, pertuzumab, and endocrine therapy vs trastuzumab, pertuzumab plus palbociclib and endocrine therapy.
And that turned out to be a positive, pivotal, FDA registrational potentially randomized phase III trial with a hazard ratio of 0.74, high statistical confidence with a couple zeros after the decimal on the P-value, and a very impressive median PFS results. 44.3 months in the experimental arm compared to 29.1 months in the control arm. So this could be practice-changing. There are some toxicities to be mindful of, in particular diarrhea and also fatigue. The incidence was about doubled for both of those adverse events to about a quarter of patients, mostly low grade, and so clinically manageable. Otherwise, the adverse event profile matched what you might expect from the simple addition of the component elements of that phase III study. So this could be a new, exciting breakthrough, if approved by the FDA, coming soon. So stay tuned.
Dr. Sara Tolaney:
Thank you, Mark. It's nice to hear the story, if you will, behind that trial, which again, it took a long time to accrue and we'd all been eagerly awaiting these data for so many years, and so nice to see such an impressive benefit. So Ian, having thought about this a lot, if you think about the CLEOPATRA data, where they didn't get endocrine therapy maintenance, and it was a different era, there were patients, only 10% of patients had seen prior HER2-directed therapy in that first line setting. You only saw about a PFS of 19 months. So maybe you could put it into context for us about maybe why we're seeing over a 40-month PFS in PATINA. What are some of the differences between the CLEOPATRA study and this? I think knowing that, should everyone get endocrine therapy, palbociclib maintenance, is it really something now we should just change our practice assuming approval and we could prescribe it routinely? Is this something you would do in everyone when you go to induction?
Dr. Ian Krop:
Yeah, no, first off, Mark, thanks for that very nice summary of the story. The preclinical data was very strong. We saw supportive clinical data from both Sara's study as well as PATRICIA, but I think we were all still pretty surprised and pleasantly surprised by the strength of the results of PATINA. I think it was the highlight, at least from my mind, of San Antonio this year.
So I think there's a couple things. I mean certainly, who should get it? I think we have to remember this is only for triple-positive patients, not for HER2-positive, hormone receptor–negative patients. And it's only for patients who had at least stable disease, if not response to their HER2 therapy, their initial HER2 therapy. So a patient has progressive disease, then these data don't really apply. But for essentially, I think, again, if the FDA, if NCCN, gets on board with this study leading to approval, I think it really does make sense for most patients. A 44-month PFS is, I think, really compelling.
Now, I think there have been a lot of interesting discussion after the data were presented on why we saw this 29-month PFS in the control arm, which, as you said, was almost close to a year more than what was seen with CLEOPATRA, even though very few of the CLEOPATRA patients had previously had HER2 therapy in the early disease setting, whereas many more in this study did.
I think it's hard to know exactly what the drivers are, but it's probably a combination of at least two things. One is, as you said, in CLEOPATRA, patients were not allowed to have endocrine therapy in the maintenance setting, whereas in this study, everybody got it. And there is, as Mark had said previously, clear data of synergy between endocrine blocking, endocrine signaling, as well as HER2 signaling. So I think the fact that the addition of the endocrine therapy certainly probably plays a role in how well both arms did on the study. And the other is that we have to remember this is a select group of patients. This wasn't looking at all patients who started taxane HP. This was only the patients who started taxane HP and had at least stable disease for six to eight cycles. And so the patients with really bad cancers who progressed early are not in this data set.
We know that's going to make the overall data look better for both arms because you're looking at a select population with a better prognosis than some. Obviously, most patients do benefit from THP, but there are still some patients who drop off because of progressive disease within those first six to eight cycles. So I think selection and the endocrine therapy are probably the two drivers of why everybody on the study did so well.
Dr. Sara Tolaney:
Thanks, Ian. I think that's really helpful context, particularly since we're not used to seeing such prolonged PFS. But I think you really hit it on the head with this is a select population. These are patients who got through induction therapy, they passed a test, if you will, and then were able to go on to maintenance. And it is interesting because 70% of these patients had actually seen HER2-directed therapy in the early disease setting. It's not what I would've thought. In the US, we're so much more used to seeing de novo disease. And so I did think that was actually very surprising that this population was predominantly a recurrent population, then, again, pass through induction then did so well. So really I think very impressive.
Mark, a common question that's come up in our group is, now we have all these people who are on HP endocrine therapy maintenance. They've been on it for a while. Should we be adding palbociclib? Maybe if they've already been on HP endocrine therapy 12, 15 months, do we need to add a CDK4 to these people? They've already demonstrated some stability without that CDK. Should it be standard? And how long do you wait post-induction to start that? Because I think this is kind of a practical question that we're running into now.
Dr. Mark Pegram:
Well, there are two schools of thought, as you know. There are the early adopters who are going to be champions of this and go all out right away. And there are more conservative investigators, and I'm probably in that camp, where I like to see peer-reviewed publication, because a lot of times things come to light that weren't available in a ten-minute abstract presentation, even with a discussant. And also you'd like to see some acknowledgement from regulatory authorities. There's no action, as yet, from the Food and Drug Administration. I think that would be really important, especially if you're considering insurance authorization, etc. That might be difficult, challenging, right now without any sort of acknowledgement from either guidelines committees, guidelines like ASCO or NCCN. That also can help win insurance authorization. So until that time, I wouldn't say that it's a standard of care as we speak today. But we're just waiting for some action to happen on either the guidelines front or the regulatory front so we can make this happen as soon as possible.
And I would probably consider patients that had already been on some maintenance therapy for a while. How long? I don't know. I mean there's no data on delayed CDK4/6 inhibition. If someone's doing pretty well just on endocrine therapy maintenance with dual antibodies, I may not have that much enthusiasm to go back and dig all those cases up out of the archives and start telling them about CDK4/6 inhibition. But it's a conversation that we probably need to have with selected patients.
Dr. Sara Tolaney:
Right.
Dr. Ian Krop:
I was hoping-
Dr. Sara Tolaney:
Well, thank you-
Dr. Ian Krop:
I was going to say, I was hoping Mark was going to tell us how many months was the proper-
Dr. Mark Pegram:
I wish.
Dr. Ian Krop:
... window because I don't know.
Dr. Mark Pegram:
I don't know either.
Dr. Sara Tolaney:
No crystal ball on that one. But I think it is an exciting time, and I would agree with Ian that this was probably the highlight of San Antonio, some of the very impressive data. So I think it does suggest that considering certainly endocrine therapy with HP maintenance after THP induction is standard. And then upon regulatory approval, I think most of us would think about adding palbociclib to that maintenance regimen.
And we do have to monitor those patients for toxicities. Certainly, Mark, as you pointed out, they do get some increased diarrhea with the combination of palbociclib with the HP maintenance. And we do have to watch out for neutropenia as well. We're not always used to monitoring white counts in the people on HP maintenance. So you do have to think about that.
But thank you so much. This does bring us to the end of this case. And please see the other segments for further discussion about the latest research in metastatic hormone receptor–positive, HER2-positive breast cancer or visit ascopost.com. Thank you so much.
