EMA Identifies 38 Cases of T-Cell Malignancies Following CAR T-Cell Therapy
Key Insights
The European Medicines Agency (search) evaluated 38 suspected cases of secondary T-cell malignancies following CAR T-cell therapy, with seven cases showing probable causality based on transgene presence in tumor samples.
The reporting rate stands at approximately one case per 1,000 patients treated with CD19 (search)- or BCMA (search)-directed CAR T-cell therapies, representing a low but identifiable risk.
EMA concluded there is reasonable possibility of causal relationship between CAR T-cell therapy and T-cell malignancy (search) development, leading to updated product information and enhanced monitoring requirements.
The European Medicines Agency (search) has concluded its comprehensive evaluation of secondary T-cell malignancies following CAR T-cell therapy, identifying 38 suspected cases across five of six approved products. The regulatory review, prompted by multiple reports at the end of 2023, represents the most extensive analysis to date of this emerging safety signal in the rapidly expanding field of cellular immunotherapy.
Comprehensive Case Analysis Reveals Concerning Pattern
Between 2018 and 2024, EMA documented cases involving patients who received tisagenlecleucel (Kymriah), lisocabtagene maraleucel (Breyanzi), axicabtagene ciloleucel (Yescarta), brexucabtagene autoleucel (Tecartus), idecabtagene vicleucel (Abecma), and ciltacabtagene autoleucel (Carvykti). The 38 cases included 15 males, 17 females, and 6 individuals with unknown sex, with a median age of 60 years ranging from 29 to 80 years.
The majority of cases originated from the United States (25 cases), with six reported within the European Economic Area. Notably, 63% of identified T-cell malignancies were diagnosed within the first 12 months following CAR T-cell therapy, with T-cell lymphoma (search) being the most frequently reported malignancy type (17 cases).
Causality Assessment Employs Novel Molecular Analysis
EMA adapted the World Health Organization-Uppsala Monitoring Centre causality assessment framework specifically for CAR T-cell products, incorporating molecular analysis as a crucial element. Of the 38 cases, only 19 underwent tumor sample testing for CAR transgene presence, revealing seven samples with CAR-positive tumor cells indicating probable causality.
"Causality was considered 'probable' in cases where a tumour sample consisted predominantly of a transgene-containing clone, in particular if the vector insertion(s) occurred in specific genomic regions that could affect cell proliferation or fate," the EMA evaluation stated. Seven cases showed negative transgene results, indicating T-cell transformation independent of vector insertion, while five cases contained low transgene copy numbers attributed to CAR T-cell infiltration rather than dominant malignant populations.
Risk Quantification in Context of Patient Population
With approximately 42,500 patients having received authorized CAR T-cell therapies by April 2024, the reporting rate stands at roughly one case per 1,000 treated patients. This figure must be interpreted against the background incidence of T-cell malignancies in patients with B-cell malignancies (search), who face an almost five-fold increased risk compared to the general population.
Studies by Chihara and colleagues reported patients with B-cell lymphoma have significantly elevated T-cell lymphoma (search) risk, while Dores and colleagues estimated an excess absolute risk of 18 cases per 100,000 person-years. Both studies found cumulative incidence of secondary T-cell neoplasms below 0.15% in these patient populations.
Regulatory Response Balances Safety and Efficacy
Following thorough analysis, EMA's Pharmacovigilance Risk Assessment Committee concluded there is reasonable possibility of causal relationship between CAR T-cell therapy and secondary T-cell malignancy (search) development. The agency classified this as a class effect applicable to all CD19 (search)- or BCMA (search)-directed products, even those without reported cases by the evaluation cutoff date.
"The benefit/risk balance for the approved CAR T-cell products remains positive, given the rarity of the event and the efficacy shown for all products in their respective indications," EMA stated. Regulatory actions include updated product information, enhanced risk management plans, and educational material for healthcare professionals.
Enhanced Monitoring Framework Established
EMA now requires marketing authorization holders to establish appropriate frameworks supporting collection and genetic testing of residual tumor samples from patients developing secondary T-cell malignancies in post-marketing settings. This represents a significant advancement in pharmacovigilance for advanced therapy medicinal products.
The agency distributed communications to relevant healthcare professionals across the European Union, raising awareness for patient monitoring requirements. Long-term follow-up studies utilizing data from the Center for International Blood and Marrow Transplant Research and European Society for Blood and Marrow Transplantation registries aim to ensure 15 years of safety monitoring.
Mechanistic Understanding Remains Limited
The underlying mechanisms driving secondary T-cell malignancy (search) development following CAR T-cell therapy remain incompletely understood. Beyond insertional mutagenesis risk, potential contributing factors include non-mutational changes during manufacturing processes, lymphodepleting chemotherapy effects, genetic predispositions, and clonal hematopoiesis.
Recent cases of CAR-negative T-cell malignancies with pre-existing clonal hematopoiesis mutations suggest CAR-mediated inflammation may drive expansion of malignant clones through multifactorial mechanisms. The accumulation of predisposing therapies, immune dysregulation, T-cell activation during manufacturing, and subsequent inflammation may collectively contribute to tumorigenesis.
Future Surveillance and Research Priorities
The evaluation highlights critical gaps in current monitoring practices, with transgene testing lacking in half of reviewed cases. Detailed documentation of patient characteristics, medical history, previous treatments, and particularly transgene testing results in tumor tissue will be essential for future causality assessments.
EMA's analysis demonstrates the value of post-marketing surveillance in identifying rare but clinically significant adverse events that may not emerge during clinical trials with limited patient numbers and follow-up periods. The agency emphasized that healthcare professionals should report suspected adverse reactions regardless of causality uncertainty, as such reporting enables comprehensive safety evaluations that ultimately benefit patient care.