Jason Luke, MD, FACP:
Stage IIB/IIC melanoma is associated with a high risk of relapse and 5-year melanoma-specific survival similar to that of stage IIIB disease.^1,2 KEYNOTE-716 is a randomized phase III trial that enrolled 976 patients aged 12 years or older with newly diagnosed, resected, and high-risk stage IIB/IIC melanoma.^3,4 Patients had negative sentinel lymph node status, no previous adjuvant therapy, and an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0/1. Patients were stratified by T category (3b vs 4a vs 4b) and pediatric status and randomized 1:1 to receive pembrolizumab 200 mg every 3 weeks or placebo for up to 17 cycles. In part 2 of the clinical trial, patients with recurrence can crossover or be rechallenged with pembrolizumab, but those data are not mature and were not presented.

The primary endpoint for the trial is investigator-assessed RFS with key secondary endpoints of DMFS, overall survival (OS), and safety. The median follow-up at this analysis was 39.4 months.

The study met the primary endpoint of significant improvement in RFS with pembrolizumab vs placebo at the first interim analysis at 12 months and maintained that improvement at 24 months.^3,5 DMFS was also significantly improved with pembrolizumab vs placebo at 24 months.⁵

The current report from KEYNOTE-716 presents the final analysis of DMFS and updated RFS.⁴

Jason Luke, MD, FACP:
At baseline, patients were well matched for age, sex, ECOG PS, T category, and disease stage.⁴ Approximately two thirds of patients had stage IIB disease.

Jason Luke, MD, FACP:
In the final DMFS analysis in the intention-to-treat population, after a median follow-up of 39.4 months, the 36-month DMFS rate was 84.4% with pembrolizumab vs 74.7% with placebo (HR: 0.59; 95% CI: 0.44-0.79).⁴ That is a 41% reduction in distant metastasis with the use of pembrolizumab in this population of patients.

Jeffrey S. Weber, MD, PhD:
These data are impressive. There is approximately a 10% absolute difference in DMFS with a break early at 6 months, which is when the first scans were done.

Jason Luke, MD, FACP:
DMFS was analyzed by stage and the benefit of adjuvant pembrolizumab was consistent for stage IIB and IIC disease.⁴ For stage IIB disease, the 36-month DMFS rate was 86.7% with pembrolizumab vs 78.9% with placebo (HR: 0.62; 95% CI: 0.42-0.92). For stage IIC disease, the 36-month rates were 80.9% and 68.1%, respectively (HR: 0.57; 95% CI: 0.36-0.88).

Jason Luke, MD, FACP:
In the prespecified DMFS subgroup analysis, all the subgroups had a benefit with pembrolizumab compared with placebo.⁴

Jason Luke, MD, FACP:
The 36-month RFS was 76.2% with pembrolizumab vs 63.4% with placebo (HR: 0.62; 95% CI: 0.49-0.79), a 38% reduction in the risk of relapse.⁴ We have seen a similar advantage for RFS as for DMFS across melanoma clinical trials in the adjuvant setting with anti–PD-1 and BRAF inhibitors.

Jeffrey S. Weber, MD, PhD:
Looking at RFS—the primary endpoint of the study—the curves have really smoothed out and I think that there will continue to be a difference between these arms over time.

Jason Luke, MD, FACP:
The 36-month RFS rates for stage IIB and stage IIC were similar.⁴ For stage IIB disease, the 36-month RFS was 79.7% with pembrolizumab vs 66.5% with placebo. For stage IIC disease, RFS was 71.4% and 58.0%, respectively.

Jason Luke, MD, FACP:
The RFS benefit was approximately the same across most of the patient populations.⁴ Patients in the United States possibly had slightly less benefit, but there are very wide CIs, which make it difficult to interpret. There is no biological reason we know that would explain why patients in the United States would derive less benefit from adjuvant anti–PD-1 than people living outside of the United States. It seems likely that these findings could be because of the relatively small number of US patients included.

Jason Luke, MD, FACP:
Safety is an important consideration in an adjuvant clinical trial. As you would expect, the rates of adverse events (AEs) are higher for the pembrolizumab group.⁴ The rate of grade 3/4 treatment-related AEs was 17.2% with pembrolizumab vs 5.1% with placebo. Regarding grade 3/4 immune-related AEs (irAEs) and infusion reactions, 11.0% of patients receiving pembrolizumab were affected vs 1.2% of patients receiving placebo. This is approximately the same as we have seen with pembrolizumab across all indications in oncology, both in the metastatic setting and in the adjuvant setting.

Jeffrey S. Weber, MD, PhD:
The mRNA-4157 (V940) individualized neoantigen therapy targets a unique mutational signature in each patient’s tumor and encodes up to 34 neoantigens. A phase I study of mRNA-4157 was previously performed in combination with pembrolizumab that found clinical responses, and the safety profile was similar to pembrolizumab alone.⁶

The KEYNOTE-942 trial enrolled 157 patients with completely resected stage IIIB-IV melanoma.⁷ Patients had to complete surgery within 13 weeks of their first dose of pembrolizumab and be disease free, with an ECOG PS of 0/1. Of importance, tissue had to be available for next-generation sequencing to make the individualized neoantigen therapy product.

Patients were stratified by disease stage and randomized 2:1 to receive mRNA-4157 plus pembrolizumab vs pembrolizumab alone. Patients received mRNA-4157 1 mg IM every 3 weeks for up to 9 doses plus pembrolizumab 200 mg IV every 3 weeks for up to 18 cycles or pembrolizumab alone at the same dose.

The primary endpoint is RFS and secondary endpoints include DMFS, safety, and tolerability. The current update at ASCO 2023 reports the first DMFS results from KEYNOTE-942.

Jason Luke, MD, FACP:
The baseline characteristics of each arm are well matched.⁷ Positive PD-L1 status is slightly more common in the combination arm, at 64.5% vs 54.0%. Tumor mutation burden (TMB) ≥10 mutations/Mb is also slightly more common with the combination vs pembrolizumab alone, at 73.8% vs 60.0%. We previously presented an analysis suggesting that PD-L1 and TMB did not make a big difference in outcomes.⁸

Jeffrey S. Weber, MD, PhD:
Earlier this year at the American Association for Cancer Research (AACR), I reported an HR of 0.561 for RFS with the combination vs pembrolizumab.⁸ There was a late break in the curve at approximately 9 months, and the 18-month RFS is 78.6% vs 62.2% This is not a trivial difference in RFS, as the HR reflects a 44% reduction in the risk of recurrence.

Jason Luke, MD, FACP:
This is quite a tremendous increase in benefit for adjuvant therapy vs pembrolizumab alone. I cannot emphasize enough that previous clinical trials of adjuvant therapy in melanoma randomized patients to placebo vs an active comparator, whereas this trial compares the combination against an active therapy, and we still see this very large benefit.

Jeffrey S. Weber, MD, PhD:
As I noted earlier, DMFS is felt by many to be a surrogate endpoint for OS. Here you see a very late break just beyond 12 months in the DMFS curve, which further separates at 18 months for a 15% absolute difference.⁷ The HR is very impressive at 0.347 (95% CI: 0.145-0.828; P = .0063).

Jason Luke, MD, FACP:
This is an astounding HR for DMFS, suggesting the combination was almost 70% better than pembrolizumab monotherapy. The caveats are that this is a phase II trial, not a phase III, and it was not powered to analyze this point. The magnitude of the HR will probably not be this high in a phase III trial. Regardless, this is a very impressive number for a clinical trial like this.

Another thing to note is that it is only after approximately 1 year of exposure to the mRNA that these curves split. I think that will be very interesting to watch in the phase III clinical trial. If mRNA-4157 becomes available outside of clinical trials, we will have to consider this potential lag time when setting expectations about what we are likely to see in terms of treatment responses.

Jason Luke, MD, FACP:
The absolute number of recurrences in this trial is not very large.⁷ The incidence of local/regional and distant recurrences are similar between the arms, suggesting that there are no major differences in relapse pattern with the addition of the individualized neoantigen therapy.

Jason Luke, MD, FACP:
There was an analysis presented for DMFS as dictated by baseline circulating-tumor DNA (ctDNA) status. This showed that ctDNA positivity at baseline is a major marker of risk.⁷

None of the patients who were ctDNA negative at baseline and received the combination regimen had a recurrence, and only a small number who received pembrolizumab monotherapy had a recurrence. But the addition of individualized neoantigen therapy made a difference for the patients who were ctDNA negative. This will be very interesting to watch.

Jason Luke, MD, FACP:
Safety in an adjuvant trial is quite important. There was a slight increase in the rates of AEs and serious AEs with the combination compared with pembrolizumab monotherapy.⁷ The rate of serious grade 3/4 AEs was 12.5% vs 8.0% for monotherapy, so not a major difference, but a suggestion that adding the individualized neoantigen therapy adds some toxicity. The toxicities added by the mRNA-4157 are injection site pain and early immune activation types of AEs. This is not surprising since it is an intramuscular injection.

Jeffrey S. Weber, MD, PhD:
The AEs associated with the vaccine, such as injection site reaction, muscle aches, fevers, and chills, that are not common with pembrolizumab alone are slightly more severe than what you would expect from a COVID-19 vaccine or a flu shot, but very few patients stopped therapy because of vaccine-related AEs.

Jeffrey S. Weber, MD, PhD:
It is important to note that the grade ≥3 irAEs were similar between the arms at 10.6% with the vaccine combination vs 14.0% with pembrolizumab.⁷ The addition of the vaccine did not increase the number of irAEs (35.6% vs 36.0% for the combination vs pembrolizumab, respectively). Most of the AEs were grade 1/2, so in my view, the combination is well tolerated.

Jason Luke, MD, FACP:
CheckMate 76K is a blinded, randomized phase III trial that enrolled 790 patients with resected stage IIB and IIC melanoma who underwent standard surgery and had a negative sentinel lymph node biopsy.⁹ Stratification was by T category and patients were randomized 2:1 to receive adjuvant nivolumab 480 mg IV every 4 weeks for 12 months or a matched placebo. This study also has an optional on-protocol open-label crossover/retreatment, although these data are not mature and were not presented.

The primary endpoint is RFS with key secondary endpoints of OS, DMFS, second progression-free survival (PFS2), and safety. The biomarker analysis was exploratory and based on the primary tumor biopsy and serum.

It was previously reported that this study met its primary endpoint with a significant improvement in RFS vs placebo (HR: 0.42; 95% CI: 0.30-0.59; P <.0001).¹⁰ The current report is an exploratory biomarker analysis that assessed recurrence rates by subgroup and the potential benefit of adjuvant nivolumab in biomarker defined subgroups.

Jason Luke, MD, FACP:
In the study, the biomarker-evaluable population included only those patients in whom these biomarkers could be identified.⁹ C-reactive protein (CRP) levels, tumor mitotic rates, CD8 T-cell infiltration, TMB, BRAF^V600 mutation status, interferon gamma signature, and PD-L1 expression on tumor cells were the biomarkers assessed in these patients.

Jason Luke, MD, FACP:
RFS outcomes were analyzed in the biomarker subgroups based on whether patients had higher vs lower biomarker levels. Patients with a higher interferon gamma signature, TMB, and CD8 T-cell infiltration had better RFS outcomes with nivolumab.⁹ However, lower levels of CRP were associated with improved RFS in the nivolumab arm. It has been known for a long time that high interferon gamma improves outcomes and CRP worsens immunotherapy outcomes, so these results were not surprising.

One interesting thing is that the mitotic rate, which we normally consider a marker of poor prognosis, did not seem to make much difference in RFS outcomes in the clinical trial.

Jason Luke, MD, FACP:
The authors did a further analysis comparing nivolumab vs placebo in patients with a higher or lower level of any of these biomarkers.⁹ Nivolumab was effective across these different scenarios, but patients had somewhat better outcomes with nivolumab vs placebo if they had higher levels of interferon gamma signature, TMB, CD8 T-cell infiltration, and tumor PD-L1 expression. As noted before, high CRP reduces the utility of nivolumab, but outcomes were still better with nivolumab compared with placebo.

Functionally speaking, these biomarkers that we have been aware of for a long time in the metastatic setting also affect the adjuvant setting. How we go forward and use them is an important question for our field.

Jason Luke, MD, FACP:
The authors also examined RFS outcomes based on biomarker median cutoffs and BRAF mutation status.⁹ Patients with BRAF-mutated tumors had better outcomes with nivolumab vs placebo, with a HR of 0.33 compared with an HR of 0.56 for wild-type tumors. This is similar to what has been seen in previous clinical trials.

Low CRP value was a strong prognostic marker for patients benefiting from immunotherapy, with an HR of 0.30 vs 0.56 for high signature. Again, these results are consistent with what we have seen previously.

Jason Luke, MD, FACP:
Neoadjuvant immunotherapy induces pathologic responses associated with favorable RFS in patients with high-risk stage III melanoma.¹¹ Response-directed therapy is emerging as a critical topic in oncology, and the trials we discuss here are trying to address that topic.

OpACIN-neo is a randomized, open-label phase II trial that enrolled 86 patients with stage IIIB/C de novo or recurrent melanoma with measurable disease.^12,13 The trial randomized patients 1:1:1 to receive standard nivolumab (1 mg/kg) plus ipilimumab (3 mg/kg), the flipped dose of ipilimumab (1 mg/kg) and nivolumab (3 mg/kg), or a sequence of ipilimumab (3 mg/kg) and nivolumab (3 mg/kg). Then patients received total lymph node dissection surgery and follow-up. The primary endpoints of OpACIN-neo are grade 3/4 irAEs within the first 12 weeks, the response rate at Week 6, and pathologic response rate at Week 6.

By contrast, the PRADO study enrolled the same population of patients, but all 99 patients received ipilimumab 1 mg/kg and nivolumab 3 mg/kg.^12,14 A marker was placed on the index lymph node, and after treatment, that lymph node was evaluated for the status of pathologic response. Patients who had a major pathologic response (≤10% viable tumor) did not have total lymph node dissection, whereas patients who had less than a major pathologic response had lymph node dissection. Patients who achieved a pathologic partial response (>10% to ≤50% viable tumor) did not receive further treatment, and patients with a pathologic nonresponse (>50% viable tumor) went on to receive adjuvant therapy with nivolumab or dabrafenib plus trametinib. The primary endpoint of PRADO is pathologic response rate in marked index lymph node and RFS at 24 months.

The current analysis of OpACIN-neo and PRADO reports the impact of total lymph node dissection on long-term survival in patients with stage III melanoma achieving a major pathologic response after neoadjuvant immunotherapy.¹² It also reports the impact of adjuvant therapy on survival in patients with pathologic nonresponse.

Jason Luke, MD, FACP:
Baseline characteristics were similar across all groups of patients.¹² The incidence of BRAF mutations ranged from 36% to 41%. The incidence of PD-L1 status <1% is approximately that same range.

Jason Luke, MD, FACP:
The incidence of major pathologic response is fairly similar from OpACIN-neo to PRADO at approximately 60%.¹² The partial pathologic response rate was 14% in OpACIN-neo and 11% in PRADO and approximately 20% had a pathologic nonresponse.

Jason Luke, MD, FACP:
Among the patients who had a major pathologic response, only a few patients relapsed or had distant metastasis.¹² That is pretty amazing when you think about how aggressive melanoma can be.

Jeffrey S. Weber, MD, PhD:
At 2.5 years of follow-up, RFS and DMFS were impressive regardless of whether patients underwent total lymph node dissection. Total lymph node dissection does not seem to be needed, which is potentially practice changing.

Jason Luke, MD, FACP:
For patients with a pathologic nonresponse to neoadjuvant therapy, not surprisingly, the addition of adjuvant therapy improved RFS and DMFS.¹² These results are important because I think we will eventually tailor neoadjuvant interventions for individual patients.

Jason Luke, MD, FACP:
Comparing adjuvant PD-1 inhibitor vs BRAF/MEK inhibitor therapy for patients who had a pathologic nonresponse to neoadjuvant therapy, there may be some slight benefit for PD-1 inhibition vs BRAF/MEK inhibition, but these are very small numbers.¹²

Jason Luke, MD, FACP:
Some patients received radiotherapy.¹² I think stacking therapies in patients nonresponsive to neoadjuvant therapy can improve outcomes over an extended period of time.

Jeffrey S. Weber, MD, PhD:
I think the take‑home lesson here is that radiation added little to efficacy. What was important is that patients with a poor neoadjuvant response absolutely need adjuvant therapy.