Cancer Immunotherapy’s Hidden Heart Risk: Landmark Review Maps Deadly Cardiac Side Effects

Immune checkpoint inhibitors have transformed modern oncology, offering durable responses in melanoma, lung cancer, renal cell carcinoma, and a growing list of other malignancies. But a new systematic review and meta-summary of 116 published case reports, appearing in the open-access journal Cancer Reports, delivers a sobering portrait of the therapy’s rarest and most dangerous complication: cardiovascular immune-related adverse events. By pooling granular, patient-level data from individual case reports rather than relying on aggregate clinical trial statistics, the researchers behind the analysis have assembled one of the most detailed real-world pictures to date of how these drugs can inflame the heart, disrupt its electrical wiring, and, in a substantial fraction of cases, prove fatal.

Immune checkpoint inhibitors work by releasing the molecular brakes that tumors place on T-cells. Agents such as pembrolizumab and nivolumab block the programmed cell death protein 1, or PD-1, pathway, while ipilimumab targets cytotoxic T-lymphocyte antigen 4, or CTLA-4. By interfering with these co-inhibitory signals, the drugs restore anti-tumor immune activity and have earned regulatory approval across metastatic melanoma, non-small cell and small cell lung cancer, renal cell carcinoma, urothelial carcinoma, hepatocellular carcinoma, and many other cancers. The trade-off is a distinctive family of immune-related adverse events, which can strike virtually any organ. An estimated 60 to 80 percent of treated patients experience some form of these toxicities, and severe, grade 3 or 4 events occur in up to 42 percent of patients receiving ipilimumab and roughly 15 percent of those on PD-1 inhibitors.

Cardiac complications sit at the extreme end of that toxicity spectrum. Reported in fewer than one percent of patients in regulatory summaries, they are nonetheless disproportionately lethal, and their presentation is often insidious. The new analysis, conducted in accordance with PRISMA guidelines, searched PubMed and Embase from inception through April 2024 for case reports describing laboratory or imaging-proven cardiovascular adverse events during treatment with pembrolizumab, nivolumab, or ipilimumab. From 1,034 initial records, the screening funnel narrowed to 116 analyzable cases: 84 involving monotherapy and 32 involving combination regimens, most commonly the nivolumab-plus-ipilimumab pairing. Each report was quality-assessed using a five-domain scoring system, and data on demographics, drug exposure, cancer type, cardiac event, treatment, and outcome were extracted into a centralized database.

The clinical picture that emerged is dominated by myocarditis, inflammation of the heart muscle itself. Among monotherapy cases, 48 instances of myocarditis were identified, with nivolumab and pembrolizumab most frequently implicated. When myocarditis occurred in isolation, mortality reached 48.1 percent, climbing to a staggering 71.4 percent among patients treated with nivolumab. Twenty-one additional cases involved myocarditis occurring alongside other syndromes, including heart block, heart failure, myositis, and myasthenia gravis, a triad sometimes described as the myositis-myocarditis-myasthenia gravis overlap syndrome. This overlap, seen in up to 30 percent of checkpoint inhibitor myocarditis cases in prior literature, complicates diagnosis and drives mortality higher. In the combination therapy group, 25 myocarditis cases were documented, mostly involving nivolumab plus ipilimumab, with seven deaths.

Beyond myocarditis, the review catalogued the full breadth of checkpoint inhibitor cardiotoxicity. Heart failure appeared in 11 monotherapy cases and five combination cases, managed with corticosteroids and guideline-directed medical therapy but still claiming five lives overall. Heart block, often a sequela of myocardial inflammation, surfaced in 10 monotherapy cases; six patients required pacing and five ultimately received permanent pacemakers, while three died. Cardiac tamponade, the life-threatening compression of the heart by fluid accumulating in the pericardial sac, was reported in 15 monotherapy cases, with pericardiocentesis and pericardial windows saving roughly 80 percent of affected patients. Rarer presentations included Takotsubo cardiomyopathy, acute coronary syndrome, vasospastic angina, sick sinus syndrome, and even pulmonary arterial hypertension, each documented in isolated reports with generally favorable outcomes.

Treatment data from the pooled cases offer practical, if imperfect, guidance. Corticosteroids were administered in 85.3 percent of cases, most often as high-dose regimens exceeding 1 milligram per kilogram per day or as 1-gram intravenous pulses of methylprednisolone. Survival appeared markedly better among patients treated with high-dose steroids than among those given low-to-moderate doses, 94.8 percent versus 66.6 percent, a pattern consistent with expert consensus from the American Society of Clinical Oncology and the National Comprehensive Cancer Network, which recommend immediate drug discontinuation, early high-dose corticosteroids, and multidisciplinary evaluation. Timing also appears critical: prior studies cited in the review suggest that patients receiving corticosteroids within 24 hours of presentation fare best, which has led many clinicians to advocate starting empiric steroids while the diagnostic workup, including troponin, NT-proBNP, electrocardiography, echocardiography, and cardiac MRI, is still underway.

For steroid-refractory cases, the review examined a patchwork of adjunctive immunosuppressive strategies. Intravenous immunoglobulin, used in 11 cases, yielded a 54.5 percent survival rate, with the best results when combined with high-dose steroids. Plasmapheresis, deployed in seven patients, produced a 57.1 percent survival rate, and in three cases was followed by immunoglobulin infusion, a sequence theorized to deliver rapid benefit followed by durable immune modulation. Pyridostigmine, given to three patients with the myasthenia overlap syndrome, was associated with 66.7 percent survival when paired with plasmapheresis. Abatacept, a CTLA-4 agonist that counteracts the very pathway some checkpoint inhibitors block, and infliximab each produced survival in the two cases in which they were used alongside high-dose steroids. By contrast, mycophenolate mofetil carried a 60 percent mortality rate in the five cases where it appeared, suggesting it may be a weaker choice, particularly as monotherapy.

Perhaps the most clinically provocative finding concerns rechallenge, the decision to resume immunotherapy after a cardiac adverse event. Among 14 patients who were rechallenged, all of whom had experienced grade 3 events, typically myocarditis or cardiac tamponade early in their treatment course, 12 survived, an 86 percent survival rate, and severe recurrence was absent. Adverse events tended to emerge between the first and sixth treatment cycles, suggesting that patients destined to develop cardiac toxicity usually do so early. The authors caution that rechallenge after grade 2 or higher myocarditis remains generally discouraged under current guidelines and should only follow multidisciplinary review, but the data indicate that, in carefully selected patients, resuming therapy after an interruption may be viable, preserving access to a cancer treatment the patient may desperately need.

The demographic patterns carry their own warnings. The cohort’s median age hovered around 65 years, and males accounted for 60.2 percent of cases, with pronounced male predominance in lung carcinoma and renal cell carcinoma. Patients with preexisting cardiac conditions such as hypertension and coronary artery disease made up 30.5 percent of the cohort, though their mortality was only modestly higher than that of cardiac-healthy patients. Intriguingly, only 4.24 percent had a documented autoimmune history, and their mortality was lower than the cohort average, hinting that baseline immune dysregulation may not universally worsen checkpoint inhibitor outcomes, a finding the authors flag as requiring larger studies. Combination regimens, by contrast, were clearly more dangerous: nivolumab-plus-ipilimumab therapy carried a mortality near 48 percent, compared with 36.1 percent for nivolumab monotherapy, reinforcing the view that intensified immune activation is the single most important risk factor for these events.

Mechanistically, the review synthesizes a growing body of evidence pointing to T-cell-mediated inflammation as the engine of checkpoint inhibitor cardiotoxicity. Mouse studies show that PD-1 deficiency predisposes to autoimmune myocarditis driven by infiltrating CD4-positive and CD8-positive T-cells and antibodies against cardiomyocytes, while PD-L1 signaling appears to protect cardiomyocytes from immune attack. The implications extend beyond the heart muscle: PET imaging studies have documented inflammatory activity in the large arteries of patients on checkpoint inhibitors, and a meta-analysis of randomized trials found a threefold increase in atherosclerotic cardiovascular events, including myocardial infarction and cerebral ischemia, among treated patients. The authors acknowledge the inherent limitations of case report methodology, including selection and publication bias and the inability to establish causality, but argue that such granular data are essential for detecting patterns, refining surveillance strategies, and ultimately building the standardized, evidence-based management algorithms that patients receiving these powerful drugs urgently need.

Subject of Research: Cardiovascular immune-related adverse events associated with immune checkpoint inhibitor cancer therapy

Article Title: Cardiovascular Immune‐Related Adverse Events of Immune Checkpoint Inhibitors: A Systematic Review and Meta‐Summary of Case Reports

Article References: Godin, S.-L., Kingma, T., Pillai, A., Kholoki, O., & Kim, A. S. (2026). Cardiovascular Immune‐Related Adverse Events of Immune Checkpoint Inhibitors: A Systematic Review and Meta‐Summary of Case Reports. Cancer Reports, 9(9), Article e70675. https://doi.org/10.1002/cnr2.70675

Image Credits: AI Generated

DOI: 10.1002/cnr2.70675

Keywords: immune checkpoint inhibitors, myocarditis, cardiotoxicity, immunotherapy, cancer, immune-related adverse events, nivolumab, pembrolizumab, ipilimumab, corticosteroids, cardiac tamponade, rechallenge