Rechallenge After Immune Checkpoint Inhibitors Myocarditis: Evidence and a Practical Framework

Central Illustration

Highlights

• •Evidence for immune checkpoint inhibitor rechallenge after myocarditis is limited but no longer purely anecdotal.
• •Highly selected patients may be rechallenged under cardio-oncology surveillance.
• •Multicenter prospective studies must define restart thresholds, monitoring intensity, and oncologic trade-offs.

Immune checkpoint inhibitors (ICIs) have transformed outcomes across multiple malignancies, but ICI myocarditis remains one of the most feared immune-related adverse events because it is uncommon, not predictable, and potentially fatal.1, 2, 3 As such, current guidance has favored permanent discontinuation, especially after symptomatic or severe myocarditis.^4,5 However, a universal, absolute contraindication to ICI rechallenge is increasingly difficult to defend. Some patients derive profound oncologic benefit from ICI therapy, some have no alternative therapies, and contemporary recognition and treatment of ICI myotoxicity have improved.^1,3 The clinical question is no longer whether rechallenge should ever occur, but rather which patients, under what conditions, and with what monitoring.

The evidence base remains limited. In the myocarditis subgroup, worldwide pharmacovigilance data suggest recurrent myocarditis after ICI rechallenge in a little over one-third of reported rechallenged cases with prior ICI myocarditis, but those estimates are derived from very small numbers (n = 16) and mixed heterogeneous phenotypes and monitoring strategies.³ A case report recently demonstrated that even life-threatening grade 4 ICI myotoxicity does not make recurrent exposure biologically impossible; in that patient, a carefully monitored nivolumab rechallenge led to a biomarker-detected recurrence that was treated early with abatacept, ruxolitinib, and corticosteroids, followed by renewed complete tumor response.⁶ Although this report is important conceptually, it does not resolve patient selection.

Informative data now come from the prospective Pitié-Salpêtrière cohort (Paris, France).⁷ Among 138 patients with definite ICI myocarditis, 14 resumed ICI therapy under a standardized cardio-oncology pathway: 7 were rechallenged after an interruption at more than 3 months, and 7 rechallenged within 3 months. Most restarted on anti-programmed cell death protein 1 monotherapy rather than combination therapy with anti-CTLA4. Only 1 patient developed recurrent grade 3 myocarditis, no patient developed severe heart failure, and postrechallenge troponin increases were usually modest (below ≈4-5 upper limit of normal) over prolonged follow-up.⁷ Importantly, rechallenge was often performed despite persistently abnormal but low-level cardiac troponin T (cTnT) (≈2-3 upper limit of normal), underscoring that the operational goal may be prevention of major adverse cardiomuscular events rather than complete biomarker normalization.⁸ These findings are descriptive, not definitive: The cohort was small, highly selected, treated at a quaternary referral center, and managed with a protocol that may not be broadly generalizable.⁷ Still, the data shift the discussion from strict contraindication to protocolized selectivity.

A practical framework starts with oncologic necessity (Figure 1). Rechallenge should be reserved for patients in whom the anticipated anticancer benefit is meaningful and alternative regimens are limited or clearly inferior and who understand the uncertainty and risk. This decision should be made through explicit shared decision-making, incorporating the patient's goals of care, risk tolerance, expected oncologic benefit, monitoring burden, and willingness to accept recurrent myocarditis risk for potential cancer-control benefit. Rechallenge should therefore be framed as a preference-sensitive decision and not a purely algorithmic one.

Figure 1.

Framework for ICI Rechallenge After Myocarditis

The figure summarizes a stepwise framework for ICI rechallenge after myocarditis, integrating oncologic need, diagnostic certainty, cardiovascular recovery, surveillance, and rescue capacity. CK = creatine kinase; ECG = electrocardiogram; ICI = Immune Checkpoint Inhibitor; NP = natriuretic peptide.

Prior depth of response matters. Oncologic justification should consider disease setting and intent, tumor ICI sensitivity, and whether progression has occurred after ICI cessation. Rechallenge is harder to justify without documented progression, given that durable disease control may persist after stopping ICI therapy for immune-related adverse events; conversely, progression after prior ICI exposure should prompt insights into the oncologic benefit from further ICI therapy as it may be limited in some settings.^9,10 Rechallenge should require a credible expectation of renewed oncologic benefit. When feasible, switching from combination therapy to a lower-risk single-agent programmed cell death protein 1 strategy may be discussed, and dose attenuation or ultra-low-dose immunotherapy may also represent an alternative in selected cases.^5,11 Rechallenge should not be pursued to satisfy therapeutic momentum alone, nor should it be deferred until performance status has substantially deteriorated, because waiting too long may narrow the chance of meaningful oncologic benefit while leaving the patient less fit to tolerate treatment.

Cardiovascular selection is equally important. Before rechallenge, the index event should be re-adjudicated for diagnostic certainty, recognizing that ICI myocarditis definition criteria have evolved as this cardiomuscular myotoxicity syndrome is better understood.^1,5,8,12,13 Definite or probable ICI myocarditis should be considered high risk, whereas suspected cases should be reassessed carefully because some ultimately reflect alternative causes of troponin elevation or cardiac symptoms. Patients should have clinical recovery from the index event, hemodynamic stability, no uncontrolled ventricular arrhythmias or high-grade conduction instability, and no ongoing respiratory muscle failure or fulminant myositis.⁷ Baseline assessment before rechallenge should include symptoms, physical examination, electrocardiogram (ECG), cTnT ideally, or otherwise cardiac troponin I (cTnI), natriuretic peptide, creatine kinase, echocardiography, Holter monitoring, and respiratory muscle evaluation as clinically indicated.^1,14,15 Risk stratification tools may refine judgment even if they were not designed specifically for rechallenge.⁸ In the International ICI-Myocarditis Registry, active thymoma, cardiomuscular symptoms, low QRS voltage, left ventricular ejection fraction less than 50%, and larger troponin rises—preferably cTnT—identified patients at greater risk for severe complications.⁸ These features should temper ICI restart.

Once the decision to resume ICI treatment has been made, ideally after multidisciplinary discussion, close clinical and biomarker monitoring are essential. Available evidence for diagnosis, risk stratification, and follow-up in ICI myocarditis relies mainly on cardiac troponin assays, with the strongest support for cTnT, but cTnI should not be ignored.^7,14 In the retrospective International ICI-Myocarditis Registry–derived risk score (≈1000 patients for discovery and validation), troponin rise modeled with cTnT was preferred over cTnI, with values exceeding 20× the upper reference limit (URL) identifying patients at higher risk for severe cardiomyotoxic complications.⁸ The 20× URL threshold is therefore best viewed as a registry-derived risk flag, not a stand-alone rule for rechallenge. Similarly, in a standardized Franco-German prospective cohort, derived biomarker data linked cTnT >32× URL to an approximately 11-fold higher risk of major cardiomuscular complications, and the prospective Pitié-Salpêtrière (Paris) ICI restart pathway used cTnT <32× URL in paucisymptomatic grade 1 to 2 cases as surveillance without a mandatory immunosuppression threshold.^1,7,8 However, no validated cTnT cutoff or relative percentage increase is currently available to define an absolute contraindication to rechallenge; therefore, these thresholds should be used for risk stratification and urgent reassessment rather than rigid rules. The practical implication is that cTnT currently carries the strongest evidence for follow-up, whereas cTnI can still inform monitoring when cTnT is unavailable or when both assays are trended serially. Persistent low-level cTnT, especially with concomitant myositis, may reflect residual cardiomuscular injury or muscle repair rather than active recurrence.¹⁴ Concern for recurrent ICI myotoxicity should be driven by a dynamic rise from baseline, particularly with new symptoms, ECG/rhythm changes, imaging changes, or respiratory involvement.

For practical use, baseline testing should be repeated frequently during the early rechallenge window—at least weekly for the first 4 to 6 weeks and then with each infusion for the first 3 months—with a rapid pathway for same-day cardio-oncology review if symptoms emerge or biomarkers rise. ECG should be repeated serially, and there should be a low threshold for echocardiography, ambulatory rhythm monitoring, or hospitalization when symptoms, conduction changes, ventricular ectopy, or troponin steep increase appear. This approach is resource intensive and favors specialized centers.⁷

Therapeutic preparedness is also essential. Rechallenge should only be attempted if severe recurrence can be recognized and treated promptly. A strategy pairing early diagnosis with abatacept- and ruxolitinib-based rescue in severe ICI myotoxicity has been associated with a marked reduction in mortality in a case series,¹ although both agents remain off-label and require experience with dosing, infection risk, and multidisciplinary coordination. Their availability is not universal. For that reason, there is currently no role for routine community-based rechallenge without specialist support. In addition, persistent low-grade biomarker abnormalities should not automatically trigger treatment escalation if the patient remains asymptomatic and stable, but rising cTnT—especially to high multiples of the URL—should prompt immediate reassessment.⁸

The central message for clinicians is balanced rather than universally permissive. Rechallenge after ICI myocarditis is not standard care, nor is it uniformly contraindicated. The emerging literature supports a patient-centered, individualized strategy centered on shared decision-making, oncologic necessity, recovery from the index event, de-escalation of immunotherapy intensity when possible, cTnT-based surveillance, and access to rapid expert rescue therapy. Several gaps persist. We need prospective multicenter validation, better biomarker-guided thresholds for rechallenge, external validation of risk tools for rechallenge candidates, and data on how rescue immunosuppression affects tumor control and rechallenge benefit. Until then, the safest position is that rechallenge may be considered in highly selected patients, within specialized cardio-oncology programs, using a protocol rather than optimism.

Funding Support and Author Disclosures

Dr Salem has obtained funding support from BeOne, AstraZeneca, BMS, and Banook Group and holds patents related to management of toxicities induced by immune checkpoint inhibitors. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.