Citation
Miller DM. Should ipilimumab be the new “standard” for refractory Merkel cell carcinoma? Journal of Cutaneous Oncology. 2024;2(1). doi:10.59449/joco.2024.05.11.
Why this question matters
Anti–PD-1 and anti–PD-L1 therapy transformed advanced Merkel cell carcinoma, but patients who progress after frontline checkpoint inhibition still face a major therapeutic gap. No FDA-approved treatment is specifically established for the post–PD-1 or post–PD-L1 setting, and many patients are unable to enroll in clinical trials because of age, frailty, poor performance status, or the logistical challenges of a rare cancer.
In practice, clinicians have increasingly turned to ipilimumab with or without nivolumab. The central question is whether the available evidence supports that approach—and whether it is strong enough to call the regimen a new standard.
Ipilimumab plus nivolumab has meaningful antitumor activity in a subset of patients with PD-1– or PD-L1–refractory MCC. The evidence supports selective use, but not the stronger claim that it should be considered a universal standard of care.
The evidence at a glance
Patients across published reports
The evidence base combined case reports, retrospective series, registry data, and one prospective study.
Objective response rate
The overall response estimate was consistent with the prospective trial and several retrospective series.
Grade 3–4 adverse events in MCC studies
Toxicity was substantial, although generally lower than in some registration trials using more intensive dosing.
Why the literature appears conflicting
Zero responses in one dual-institution cohort
Thirteen patients treated at BWH/DFCI and MGH had no objective responses, with median progression-free survival of 1.3 months and median overall survival of 4.7 months.
Higher responses in other series
Johns Hopkins/Fred Hutchinson and the ADOREG registry reported response rates of approximately 31% and 50%, respectively.
Prospective evidence supports activity
The only prospective trial reported a 31% objective response rate, with no clear added benefit from stereotactic body radiotherapy.
Patient selection may explain some variation
Performance status, disease tempo, timing of treatment, prior therapy, and dosing may strongly influence the chance of benefit.
Applying a regulatory evidence framework
A useful way to judge the evidence is to ask whether it isolates the treatment effect, provides statistically persuasive results, and has been externally replicated. In refractory MCC, objective response rate is a practical endpoint because spontaneous tumor regression is uncommon, but response remains a surrogate rather than a direct demonstration of improved survival or quality of life.
- The aggregate response rate supports a real antitumor effect.
- The lower confidence bound reduces the likelihood that all responses reflect rare delayed effects or chance.
- The evidence is drawn largely from single-arm studies without a true comparator.
- Progression-free and overall survival effects cannot be cleanly isolated.
- External replication is incomplete, particularly at the prospective level.
The data are persuasive enough to support clinical use in selected patients, but not definitive enough to imply that ipilimumab plus nivolumab should replace individualized decision-making, clinical-trial enrollment, or alternative approaches for every patient with refractory MCC.
Who may be most likely to benefit?
- Younger or physiologically fit patients with good performance status.
- Patients whose disease progression is recognized before substantial clinical decline.
- Patients able to tolerate the immune toxicity of combined CTLA-4 and PD-1 blockade.
- Patients without a more compelling clinical-trial option.
- Patients for whom the potential for durable response justifies a substantial risk of toxicity.
For older, frail, or functionally declining patients, the probability of benefit may be lower and the treatment burden more consequential. In such settings, local treatment, less intensive systemic therapy, or a comfort-focused approach may better align with patient goals.
A practical treatment implication
The editorial raises the possibility that clinicians should assess response to frontline PD-1 or PD-L1 therapy early—potentially after two doses—and avoid prolonged ineffective treatment when disease is clearly progressing. Earlier transition to salvage therapy may allow treatment while performance status remains adequate, although this approach remains hypothesis-generating rather than prospectively validated.
Ipilimumab plus nivolumab is a reasonable salvage option for carefully selected patients with anti–PD-1 or anti–PD-L1–refractory MCC. It is not a dependable default for every patient, and most treated patients will still not experience an objective response.
What the field still needs
- Prospective confirmation of response and survival outcomes.
- Better predictors of who is likely to benefit or experience severe toxicity.
- More effective strategies for the majority of patients who do not respond.
- Earlier identification of frontline resistance.
- Rare-disease trial designs that remain feasible for older and functionally vulnerable patients.
Author
David M. Miller.