The patient arrived with intrahepatic cholangiocarcinoma, an aggressive cancer of the bile ducts within the liver, and received two doses of immune checkpoint inhibitor therapy. Shortly afterward, her blood tests revealed a striking pattern of myocardial injury. Cardiac troponin T, a protein released when heart muscle cells die, climbed to 0.263 nanograms per milliliter, nearly nineteen times the upper limit of the normal range of less than 0.014. Creatine kinase reached 647 units per liter against a normal ceiling of 140, the myocardial band fraction of that enzyme hit 38 units per liter where the normal range tops out at 23, and myoglobin surged to 515 nanograms per milliliter, far above the normal maximum of 58. Yet paradoxically, her initial electrocardiogram showed no arrhythmia, her echocardiogram was unremarkable, and her left ventricular ejection fraction stood at a healthy 65 percent. Coronary computed tomography revealed only mild stenosis, and cardiac magnetic resonance imaging came back negative.

This disconnect between laboratory evidence of heart injury and reassuring imaging is precisely what makes immune checkpoint inhibitor-associated myocarditis, abbreviated ICIAM, so treacherous. After a multidisciplinary team discussion excluded alternatives such as viral myocarditis and significant coronary artery disease, the clinicians diagnosed ICIAM based on the temporal relationship to immunotherapy and the characteristic biomarker profile. The team immediately suspended all anti-tumor treatment and began intravenous methylprednisolone at 2 milligrams per kilogram of body weight, 120 milligrams per day for three days, the first-line therapy recommended by the European Society of Cardiology guidelines on cardio-oncology. In many patients, high-dose corticosteroids rapidly suppress the aberrant immune attack, and troponin levels fall. In this patient, they did not.

During steroid therapy, her troponin T declined only marginally, from 0.263 to 0.187 nanograms per milliliter, a drop far short of the 50 percent reduction from peak that defines a steroid-responsive case. This failure established the diagnosis of steroid-resistant ICIAM, a subset of the condition associated with a grim prognosis and, until recently, no established effective therapy. The reported mortality of ICIAM overall ranges from 39.7 to 66 percent, and steroid-resistant cases fare worst of all. Recognizing the stakes, the team added tofacitinib, a Janus kinase inhibitor that blocks intracellular signaling pathways used by pro-inflammatory cytokines, at a dose of 5 milligrams twice daily. The hope was that shutting down JAK-mediated cytokine signaling would break the immune assault on the myocardium that steroids alone could not extinguish.

Instead, the disease escalated. Troponin levels rose further, and a new electrocardiographic abnormality emerged: frequent premature ventricular contractions, extra heartbeats originating in the ventricles that signal electrical instability of the heart muscle. In the context of ongoing myocarditis, such arrhythmias can presage malignant rhythms and sudden cardiac death. The clinicians now faced a patient whose heart inflammation was resisting both the standard of care and the first escalation. Drawing on their center’s prior experience and on the ratio of CD4 to CD8 lymphocytes in the patient’s peripheral blood mononuclear cells, which stood at 3.1 against a normal range of 0.6 to 2.9 and pointed to a skewed immune activation state, they added mycophenolate mofetil, an inhibitor of guanine nucleotide synthesis that suppresses lymphocyte proliferation, at 7.5 grams twice daily, combined with intravenous immunoglobulin at 10 grams per day for five days as intensive immunosuppressive therapy.

The response was decisive. Troponin T levels began a gradual, sustained decline, and the ventricular arrhythmia resolved, with follow-up electrocardiograms returning to normal. The patient achieved complete remission of the myocarditis, and, critically, her anti-tumor treatment was successfully rechallenged once the cardiac complication was stably controlled. That final step matters enormously in clinical practice. Myocarditis forces clinicians to stop the very drugs controlling a patient’s cancer, and permanent discontinuation can leave an aggressive malignancy unchecked. Demonstrating that the myocarditis can be brought under control and immunotherapy resumed converts a life-threatening side effect from an automatic end of treatment into a manageable detour.

The mechanistic backdrop helps explain why this case unfolded as it did. Immune checkpoint inhibitors block inhibitory receptors such as PD-1 and CTLA-4, releasing brakes on T cells so they can attack tumors. In susceptible individuals, that release of restraint extends to self-reactive immune clones, and the heart becomes a target. Research, including a 2024 study in Nature that mapped immune responses across the heart, blood, and tumor in checkpoint myocarditis, shows infiltration of the myocardium by activated immune cells and a storm of pro-inflammatory cytokines. High-risk populations include patients receiving combination immunotherapy, whether dual checkpoint inhibitors or checkpoint inhibitors paired with chemotherapy or anti-angiogenic agents, and those with diabetes, pre-existing cardiovascular disease, higher body mass index, or advanced age. This patient, at 77 with cholangiocarcinoma, fit squarely within the vulnerable demographic.

The therapeutic landscape for steroid-resistant disease remains unsettled, which is what makes documented cases so valuable. Several agents are under investigation as second-line options: tofacitinib and its fellow JAK inhibitor baricitinib, which animal and early clinical work suggests protects the myocardium by targeting JAK1/STAT3 signaling to modulate macrophage polarization; mycophenolate mofetil; anti-thymocyte globulin, an antibody that depletes T cells; intravenous immunoglobulin; tocilizumab, an interleukin-6 receptor blocker; abatacept, a CTLA-4 agonist that restores inhibitory signaling to T cells; alemtuzumab, an anti-CD52 antibody; and plasma exchange. European Society of Cardiology guidelines recommend considering second-line immunosuppression when steroids fail, but they stop short of endorsing any specific regimen, instead recommending multidisciplinary team discussion. The Shanghai group notes that in their center, tofacitinib has provided clinical benefit when used early in steroid-resistant patients, though some patients resist it, and mycophenolate mofetil has shown potential benefit in exactly those situations, as this case illustrates.

The sequencing in this patient carries the report’s central lesson. Tofacitinib alone, added on top of methylprednisolone, did not halt the injury; troponin continued to climb and arrhythmias appeared. Only with the addition of mycophenolate mofetil, guided by the abnormal CD4-to-CD8 ratio, did the inflammatory cascade collapse. The authors interpret this as evidence that early administration of second-line immunosuppressive therapy, tailored and intensified rather than delayed, is crucial for good outcomes in steroid-resistant ICIAM. The phrase early administration recurs throughout their discussion because the window is narrow: myocarditis driven by unleashed T cells can progress from biomarker elevation to fatal arrhythmia within days, and median onset of the condition falls between 17 and 65 days after starting immunotherapy, meaning the danger period spans the very weeks when patients and clinicians are most optimistic about the cancer treatment itself.

For the growing population of patients receiving checkpoint inhibitors worldwide, this case is a reminder that the revolution in cancer immunotherapy carries a cardiac shadow that demands vigilance. Troponin monitoring after immunotherapy initiation, a low threshold for multidisciplinary consultation, and readiness to escalate beyond steroids within days rather than weeks form the practical take-home framework. No single case can establish which second-line regimen is superior, and the authors themselves emphasize the current lack of data to recommend one specific protocol. But by documenting a complete remission achieved with tofacitinib, mycophenolate mofetil, and immunoglobulin, followed by a safe return to anti-cancer therapy, the Zhongshan Hospital team has added a concrete, clinically actionable data point to a field where every documented survival matters. As immunotherapy expands to more tumor types and earlier disease stages, the number of patients exposed to this rare but lethal risk will only grow, and the accumulated experience of cases like this one will shape the guidelines that keep them alive.

Subject of Research: Steroid-resistant myocarditis caused by immune checkpoint inhibitor cancer therapy and its treatment with second-line immunosuppressive drugs

Article Title: Steroid-resistant immune checkpoint inhibitor-associated myocarditis: a case report

Article References: He, X., Zhang, Y., Wang, Y., Chen, H., Liu, Y., & Cheng, L. (2025). Steroid-resistant immune checkpoint inhibitor-associated myocarditis: a case report. Clinical Cancer Bulletin, 4(1), Article 5. https://doi.org/10.1007/s44272-025-00033-3

Image Credits: AI Generated

DOI: 10.1007/s44272-025-00033-3

Keywords: immune checkpoint inhibitors, myocarditis, immunotherapy, troponin, tofacitinib, mycophenolate mofetil, cardiotoxicity, immunosuppression, cholangiocarcinoma, steroid resistance, arrhythmia, cardio-oncology