Host Dr. Davide Soldato and guest Dr. Harriet Kluger discuss the JCO article "Phase II Trial of Pembrolizumab in Combination With Bevacizumab for Untreated Melanoma Brain Metastases."

Transcript

The guest on this podcast episode has no disclosures to declare.

Dr. Davide Soldato

Hello and welcome to JCO After Hours, the podcast where we sit down with authors from some of the latest articles published in the Journal of Clinical Oncology. I am your host, Dr. Davide Soldato, Medical Oncologist at Ospedale San Martino in Genoa, Italy. Today, we are joined by JCO author Dr. Harriet Kluger. Dr. Kluger is a professor of medicine at Yale School of Medicine, Director of the Yale SPORE in Skin Cancer, and an internationally recognized expert in immuno-oncology for melanoma and renal cell carcinoma. She leads early-phase and translational trials that pair novel immunotherapies with predictive biomarkers to personalized care.

Today, Dr. Kluger and I will be discussing the article titled "Phase 2 Trial of Pembrolizumab in Combination with Bevacizumab for Untreated Melanoma Brain Metastases." In this study, Dr. Kluger and colleagues evaluated four cycles of pembrolizumab plus the anti-VEGF antibody bevacizumab followed by pembrolizumab maintenance in patients with asymptomatic non-hemorrhagic melanoma brain metastases that had not previously received PD-1 therapy.

Thank you for speaking with us, Dr. Kluger.

Dr. Harriet Kluger

Thank you for inviting me. The pleasure is really all mine.

Dr. Davide Soldato

So to kick off our podcast, I just wanted to ask if you could outline a little bit the biological and clinical rationale that led you to test this type of combination for patients with untreated brain metastases from metastatic melanoma.

Dr. Harriet Kluger

Back in approximately 2012, patients who had untreated brain metastases were excluded from all clinical trials. So by untreated, I mean brain metastases that had not received local therapy such as surgery or radiation. The reason for it was primarily because there was this fear that big molecules wouldn't penetrate brain lesions because they can't pass the blood-brain barrier. Turns out that the blood-brain barrier within a tumor is somewhat leaky and drugs sometimes can get in there.

When PD-1 inhibitors were first identified as the next blockbuster class of drugs, we decided to conduct a phase 2 clinical trial of pembrolizumab monotherapy in patients with untreated brain metastases. We actually did it also in lung cancer, and we could talk about that later on. Responses were seen. The responses in the brain and the body were similar. They were concordant in melanoma patients.

Now, at approximately that time, also another study was done by the Australian group by Dr. Georgina Long, where they did a randomized trial where patients who didn't require immediate steroid therapy received either nivolumab alone or nivolumab with ipilimumab, and the combination arm was substantially superior. Subsequently, also, Bristol Myers Squibb also conducted a large phase 2 multicenter trial of ipilimumab and nivolumab in patients with untreated brain metastases. And there, once again, they saw that the responses in the brain were similar to the responses in the body.

Now, somewhere along the line there, we completed our anti-PD-1 monotherapy trial. And when we looked at our data, we still didn't have the data on ipilimumab and nivolumab. And our question was, “Well, how can we do better?” Just as we're always trying to do better. We saw two really big problems. One was that patients had a lot of perilesional edema. And the other one was that we were struggling with radiation necrosis in lesions that were previously Gamma Knifed. The instance of radiation necrosis was in excess of 30%.

So the rationale behind this study was that if we added bevacizumab, maybe we could treat those patients who had some edema, not requiring steroids, but potentially get them on study, get that PD-1 inhibitor going, and also prevent subsequent radiation necrosis. And that was the main rationale behind the study. We had also done some preclinical work in mouse models of melanoma brain metastases and in an in vitro blood-brain barrier model where we showed that bevacizumab, or anti-VEGF, really tightens up those leaky basement membranes and therefore would be very likely to decrease the edema.

Dr. Davide Soldato

Thank you very much for putting in context the combination. So this was a phase 2 trial, and you included patients who had at least one lesion, and you wanted lesions that were behind 5 and 20 millimeters. Patients could be included also if the brain metastasis was higher in dimension than 20 millimeters, but it had to be treated, and it was then excluded from the evaluation of the primary objective of the trial. So regarding, a little bit, these characteristics, do you think that this is very similar to what we see in clinical practice? And what does this mean in terms of applicability of these results in clinical practice?

Dr. Harriet Kluger

So that's an excellent question. The brain metastasis clinical research field has somewhat been struggling with this issue of inclusion/exclusion criteria. When we started this, we showed pretty clearly that 5 to 10 millimeter lesions, which are below the RECIST criteria for inclusion, are measurable if you use MRIs with slices that are 1 to 2 millimeters. Most institutions in the United States do use these high-resolution MRIs. I don't know how applicable that is on a worldwide scale, but we certainly lowered the threshold for inclusion so that patients who have a smattering of small brain metastases would be eligible.

Now, patients with single large brain metastases, the reason that we excluded those from the trial was because we were afraid that if a patient didn't respond to the systemic therapy that we were going to give them, they could really then develop severe neurological symptoms. So, for patient safety, we used 20 millimeters as the upper level for inclusion. Some of the other trials that I mentioned earlier also excluded patients with very large lesions. Now, in practice, one certainly can do Gamma Knife therapy to the large lesions and leave the smaller ones untreated. So I think it actually is very applicable to clinical practice.

Dr. Davide Soldato

Thank you very much for that insight, because I think that sometimes criteria for clinical trials, they have to be very restrictive. But then we know that in clinical practice, the applicability of these results is probably broader.

So, going a little bit further in the results of the study, I just wanted a little bit of comment from you regarding what you saw in terms of intracranial response rate and duration of response among patients who obtained a response from the combination treatment.

Dr. Harriet Kluger

So we were actually surprised. When we first designed this study, as I said earlier, we weren't trying to beat out ipilimumab and nivolumab. We were really just trying to exclude those patients who wouldn't have otherwise been eligible for ipilimumab and nivolumab because of edema or possibly even previous radiation necrosis. So it was designed to differentiate between a response rate of 34%, and I believe the lower bound was somewhere in the 20s, because that's what we'd seen in the previous pembrolizumab study.

What we saw in the first 20 patients that we enrolled was actually a response rate that far exceeded that. And so we enrolled another cohort to verify that result because we were concerned about premature publishing of a result that we might have achieved just by chance. The two cohorts were very similar in terms of the response rates. And certainly this still needs to be verified in a second study with additional institutions. We did include the Moffitt Cancer Center, and the response rate with Moffitt Cancer Center was very similar to the Yale Cancer Center response rate.

Now, your other question was about duration of response. So the other thing that we started asking ourselves was whether this high response rate was really because the administration of the anti-VEGF will decrease the gadolinium enhancement and therefore we might actually just be seeing prettier scans but not tumor shrinkage. And the way to differentiate those two is by looking at the duration of the response. Median progression-free survival was 2.2 years. That's pretty long. The upper bound on the 95% confidence interval was not reached. I can't tell you that the duration is as good as the duration would be when you give ipilimumab. Perhaps it is less good. This was a fairly sick population of patients, and it included some who might not have been able to receive ipilimumab and nivolumab. So it provides an alternative. I do believe that we need to do a randomized trial where we compare it to ipilimumab and nivolumab, which is the current standard of care in this patient population. We do need to interpret these results with caution.

I also want to point out regarding the progression-free survival that we only gave four doses of anti-VEGF. So one would think that even though anti-VEGF has a long half-life of three or four weeks, two years later, you no longer have anti-VEGF effect, presumably. So it does something when it's administered fairly early on in the course of the treatment.

Dr. Davide Soldato

So, in terms of clinical applicability, do you see this combination of pembrolizumab and bevacizumab - and of course, as we mentioned, this was a phase 2 trial. The number of patients included was not very high, but still you saw some very promising results when compared with the combination of ipilimumab and nivolumab. So do you see this combination as something that should be given particularly to those patients who might not be able to receive ipilimumab and nivolumab? So, for example, patients who are very symptomatic from the start or require a high dose of steroids, or also to provide a quicker response in terms of patients who have neurological symptoms, or do you think that someday it could be potentially used for all patients?

Dr. Harriet Kluger

The third part of your question, whether it can be used someday for all patients: I think we need to be very careful when we interpret these results. The study was substantially smaller than the ipilimumab/nivolumab trial that was conducted by Bristol Myers Squibb. Also going to point out that was a different population of patients. Those were all frontline patients. Here we had a mix of patients who'd had previous anti-CTLA-4 and frontline patients. So I don't think that we can replace ipilimumab and nivolumab with these results. But certainly the steroid-sparing aspect of it is something that we really need to take into consideration. A lot of patients have lesions in locations where edema can be dangerous, and some of them have a hard time coming off the steroids. So this is certainly a good approach for those folks.

Dr. Davide Soldato

And coming back to something that you mentioned in the very introduction, when you said that there were two main problems, which was one, the problem of the edema, and the second one, the problem of the radionecrosis. In your trial, there was a fair percentage of patients who received some type of local treatment before the systemic one. So the combination of pembrolizumab and bevacizumab. And most of the patients received radiosurgery. So I just wanted a brief comment regarding the incidence of radionecrosis in the trial and whether that specific component of the combination with bevacizumab was reduced. And how do you think that this fares in terms of what we see in clinical practice in terms of radionecrosis?

Dr. Harriet Kluger

I'm not sure that we really reduced the incidence of radiation necrosis. We saw radiation necrosis here. We saw less of it than in the trial of pembrolizumab monotherapy, but these were also different patients, different time. We saw more than we thought that we were going to see. It was 27%, I believe, which is fairly high still. We only gave the four doses of bevacizumab. Maybe to really prevent radiation necrosis, you have to continue to give the bevacizumab. That, too, needs to be tested. The reason that we gave the four doses of bevacizumab was simply because of the cost of the bevacizumab at the time.

Dr. Davide Soldato

Thank you very much for that comment on radionecrosis. And I really think that potentially this is a strategy, so continuing the bevacizumab, that really makes a lot of sense, especially considering that the tolerability of the regimen was really very, very good, and you didn't see any significant or serious adverse events related to bevacizumab. So just wondering if you could comment a little bit on the toxicities, whether you had anything unexpected.

Dr. Harriet Kluger

There was one patient who had a microperforation of a diverticulum, which was probably related to the bevacizumab. It was conservatively managed, and the patient did fine and actually remains alive now, many years later. We had one patient who had dehiscence of a previous wound. So there is some. We did not see any substantial hypertension, proteinuria, but we only gave the four doses. So it is possible that if you give it for longer, we would see some side effects. But still, relative to ipilimumab, it's very, very well tolerated.

Dr. Davide Soldato

Yeah, exactly. I think that the safety profile is really different when we compare the combination of ipilimumab/nivolumab with the pembrolizumab/bevacizumab. And as you said, this was a very small trial and probably we need additional results. But still, these results, in terms of tolerability and safety, I think they are very interesting.

So one additional question that I think warrants a little bit of comment on your part is actually related to the presence of patients with BRAF mutation and, in general, to what you think would be the best course of treatment for these patients who present with the upfront brain metastases. So this, it's actually not completely related to the study, but I think that since patients with BRAF mutation were included, I think that this warrants a little bit of discussion on your part.

Dr. Harriet Kluger

So we really believe that long-term disease control, particularly in brain metastases, doesn't happen when you give BRAF/MEK inhibitors. You sometimes get long-term control if you've got oligometastatic disease in extracranial sites and if they've previously been treated with a lot of immune checkpoint inhibitors, which wasn't the case over here. So a patient who presents early in the course of the disease, regardless of their BRAF status, I do believe that between our studies and all the studies that have been done on immunotherapy earlier in the course of disease, we should withhold BRAF/MEK inhibitors unless they have overwhelming disease and we need immediate disease control, and then we switch them very quickly to immunotherapy.

Can I also say something about the toxicity question from the bevacizumab? I have one more comment to make. I think it's important. We were very careful not to include patients who had overt hemorrhage from brain metastases. So melanoma brain metastases relative to other tumor types tend to bleed, and that was an exclusion criteria. We didn't see any bleeding that was attributable to the bevacizumab, but we don't know for sure that, if this is widely used, that that might not be a problem that's observed. So I would advise folks to use extreme caution and perhaps not use it outside of the setting of a clinical trial in patients with overt hemorrhage in the melanoma brain metastases.

Dr. Davide Soldato

Thank you very much. I think that one aspect that is really interesting in the trial is actually related to the fact that you collected a series of biomarkers, both circulating ones, but also some that were collected actually from the tissue. So just wondering if you could explain a little bit which type of biomarkers you evaluated and whether you saw any significant results that could suggest higher or lower efficacy of the combination.

Dr. Harriet Kluger

Thank you for that. So yes, the biomarker studies are fairly exploratory, and I want to emphasize that we don't have anything that's remotely useful in clinical practice at this juncture. But we did see an association between vessel density in the tumors and improved response to this regimen. So possibly those lesions that are more vascular are more fed by or driven by VEGF, and that could be the reason that there was improved response. We also saw that when there was less of an increase in circulating angiopoietin-2 levels, patients were more likely to respond. Whether or not that pans out in larger cohorts of patients remains to be determined.

Dr. Davide Soldato

Still, do you envision validation of these biomarkers in a potentially additional trial that will evaluate, again, the combination? Because I think that the signals were quite interesting, and they really make sense from a biological point of view, considering the mechanism of action of bevacizumab. So I think that, yeah, you're right, they are exploratory. But still, I think that there is very strong biological rationale. So really I wanted to congratulate you on including that specific part and on reporting it. And so the question is, really, do you envision validation of these biomarkers in larger cohorts?

Dr. Harriet Kluger

I would hope to see that, just as I'd like to see validation of the clinical results as well. The circulating biomarkers are very easy to do. It's a simple ELISA test. And the vessel density on the tumor is essentially CD34 staining and units per area of tumor. Also very simple to do. So I'd love to see that happen.

Dr. Davide Soldato

Do you think that considering the quality of the MRI that we are using right now, it would be possible to completely bypass even the evaluation on the tissue? Like, are we going in a direction where we can, at a certain point, say the amount of vessels that we see in these metastases is higher versus lower just based on MRI results?

Dr. Harriet Kluger

You gave me an outstanding idea for a follow-up study. I don't know whether you can measure the intensity of gadolinium as a surrogate, but certainly something worth asking our neuroradiology colleagues. Excellent idea. Thank you.

Dr. Davide Soldato

You're welcome. So just moving a step further, we spoke a lot about the validation of these results and the combination. And just wanted your idea on what do you think it would be more interesting to do: if designing a clinical trial that really compares pembrolizumab/bevacizumab with ipilimumab and nivolumab or going directly for the triplet. So we know that there has been some type of exploration of triplet combination in metastatic melanoma. So just your clinical impression: What would you do as an investigator?

Dr. Harriet Kluger

So it's under some discussion, actually. It's very difficult to compare drugs from different companies in an investigator-initiated trial. Perhaps our European colleagues can do that trial for us. In the United States, it's much harder, but it can be done through the cooperative groups, and we are actually having some discussions about that. I don't have the answer for you. It would be lovely to have a trial that compared the three drugs to ipi/nivo and to pembrolizumab/bevacizumab. So a three-arm trial. But remember, these are frontline melanoma patients. There aren't that many of them anymore like there used to be. So accrual will be hard, and we have to be practical.

Dr. Davide Soldato

Yeah, you're right. And in the discussion of the manuscript, you actually mentioned some other trials that are ongoing, especially one that is investigating the combination of pembro and lenvatinib, another one that is investigating the combination of nivolumab and relatlimab. So just wondering, do you think that the molecule in terms of VEGF inhibition, so bevacizumab versus lenvatinib, can really make a difference or is going to be just a mechanism of action? Of course, we don't have the results from this trial but just wondering if you could give us a general comment or your opinion on the topic.

Dr. Harriet Kluger

So that's a really great question. The trial of pembrolizumab and lenvatinib was our answer to the fact that bevacizumab is not manufactured by the same company as pembrolizumab, and we’re trying to give a practical answer to our next study that might enable us to take this approach further. But it does turn out from our preclinical studies that bevacizumab and VEGF receptor inhibition aren't actually the same thing in terms of the effects on the blood-brain barrier or the perilesional tumor microenvironment in the brain. And these studies were done in mice and in in vitro models. Very different effects. The lenvatinib has stronger effect on the tumors themselves, the tumor cells themselves, than the bevacizumab, which has no effect whatsoever. But the lenvatinib doesn't appear to tighten up that blood-brain barrier.

Dr. Davide Soldato

Thank you. I think that's very interesting, and I think it's going to be interesting to see also results of these trials to actually improve and give more options to our patients in terms of different mechanism of action, different side effects. Because in the end, one thing that we discussed is that some combination may be useful in some specific clinical situation while others cannot be applicable, like, for example, an all immunotherapy-based combination.

Just one final comment, because I think that we focused a lot on the intracranial response and progression-free survival. You briefly mentioned this but just wanted to reinforce the concept. Did you see any differences in terms of intracranial versus extracranial response for those patients who also had extracranial disease with the combination of pembro and bevacizumab?

Dr. Harriet Kluger

So the responses were almost always concordant. There were a couple of cases that might have had a body response and not an intracranial response and vice-versa, but the vast majority had concordant response or progression. We do believe that it's a biological phenomenon. The type of tumor that tends to go to the brain is going to be the type of tumor that will respond to whatever the regimen is that we're giving. In the previous trial also, we saw concordance of responses in the body and the brain.

Dr. Davide Soldato

Thank you very much. Just to highlight that really the combination is worth pursuing considering that there was not so much discordant responses, and the results, even in a phase 2 trial, were very, very promising.

So thank you again, Dr. Kluger, for joining us today and giving us a little bit of insight into this very interesting trial.

Dr. Harriet Kluger

Thank you for having me.

Dr. Davide Soldato

So we appreciate you sharing more on your JCO article titled "Phase 2 Trial of Pembrolizumab in Combination with Bevacizumab for Untreated Melanoma Brain Metastases," which gave us the opportunity to discuss current treatment landscape in metastatic melanoma and future direction in research for melanoma brain metastasis.

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