# Secondary T-cell malignancy after CAR-T, and what the FDA's 2024 action actually says

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OnCo record `rejuv-tx-secondary-t-cell-malignancy` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

In 2024 the US regulator added a warning to every approved CAR-T product about T-cell cancers after treatment. It says the risk applies to the class, that these can appear within weeks, and that patients should be monitored for life. It does not say CAR-T causes most of them, and published series find them very rare.

## Summary

What happened, in order. In November 2023 the FDA posted a safety communication about reports of T-cell malignancies, including CAR-positive lymphoma, in patients who received BCMA-directed or CD19-directed autologous CAR-T immunotherapies, drawn from clinical trial and postmarketing sources. It also listed post-treatment T-cell malignancy as a potential signal of serious risk in its FAERS quarterly report for July to September 2023. The agency then concluded, on evaluation of postmarketing adverse event and clinical trial reports, that mature T-cell malignancies including CAR-positive tumours may present as soon as weeks following infusion and may include fatal outcomes, and that the serious risk applies to all currently approved BCMA-directed and CD19-directed genetically modified autologous CAR-T products: Abecma, Breyanzi, Carvykti, Kymriah, Tecartus and Yescarta. In January 2024 it initiated class safety labelling changes, and it determined that changes to the Boxed Warning were warranted, with related updates to Warnings and Precautions, Postmarketing Experience, Patient Counseling Information and the Medication Guide.

What the action requires. The FDA states that patients and clinical trial participants receiving treatment with these products should be monitored life-long for secondary malignancies, and that in the event a new malignancy occurs the manufacturer should be contacted to report it and to obtain instructions on collecting patient samples for testing for the presence of the CAR transgene. That last clause is the one that matters scientifically: it is how the question of causation gets answered case by case.

What the action does not say. It does not state an incidence. It does not attribute these malignancies to vector integration. It does not withdraw a product, narrow an indication or change the benefit-risk conclusion for any approved use. The two FDA officials who wrote about it in the New England Journal of Medicine framed it as a signal requiring surveillance within a class whose benefit remains established.

What the published data show. A single-centre analysis of 449 patients treated with commercial CD19 or BCMA CAR-T reported one T-cell lymphoma, occurring three months after anti-CD19 CAR-T for non-Hodgkin lymphoma and diagnosed from a thoracic lymph node during surgery for lung cancer. It had a CD8-positive cytotoxic phenotype and a JAK3 variant, and the CAR transgene was very low; the T-cell clone had been present at low level in the blood before the CAR-T infusion and in the lung cancer. In the same 449 patients, at a median follow-up of 10.3 months, 16 patients, 3.6 per cent, had a second primary malignancy, with median onset of 26.4 months for solid and 9.7 months for haematological malignancies, and projected five-year cumulative incidence of 15.2 per cent for solid and 2.3 per cent for haematological. The authors' conclusion was that a single case of T-cell lymphoma suggested a low risk.

A 2026 review drawing on pivotal trials, registries, meta-analyses, pharmacovigilance data and molecular case reports states that registry data and large institutional series consistently show secondary T-cell malignancies to be exceedingly rare, with reported incidences of approximately 0.03 to 0.3 per cent depending on the cohort, and far less common than therapy-related myeloid neoplasms, solid tumours and non-melanoma skin cancers in heavily pretreated populations. It states that most molecularly characterised post-CAR-T lymphomas lack evidence of CAR vector-driven transformation and appear to reflect pre-existing or therapy-selected clonal T-cell populations in the context of clonal haematopoiesis, immune dysregulation and in some cases viral reactivation.

And the exception that proves the mechanism is possible. A case reported in 2025 described a T-cell lymphoma harbouring a lentiviral CAR integration in TP53, a known tumour suppressor, arising in a patient with multiple myeloma after BCMA-directed CAR-T. The authors' own framing is that malignant T-cell transformation after CAR-T has been described but the contribution of CAR integration to oncogenesis has not been clear; this case demonstrates that vector-driven transformation can occur. One demonstrated case does not establish a rate, and the 2026 review describes such cases as exceptional and probably dependent on cooperating host or clonal events.

How to hold all of that at once. The regulator identified a class signal and responded with labelling and lifelong monitoring rather than restriction, which is a proportionate response to a rare and serious event of uncertain causation. The published incidence is in the range of three in ten thousand to three in a thousand. Second cancers of all kinds after CAR-T are considerably commoner than T-cell lymphoma specifically, and the population receiving CAR-T has usually had years of prior cytotoxic therapy, so clonal haematopoiesis and therapy-related neoplasms are expected in it regardless. The practical consequence for a person who has had CAR-T is the one the FDA states: new cancers are looked for for life, and if one appears, the sample is tested for the transgene so that the question is answered rather than assumed.

## Fields

- Kind: Technology
- Status: established
- Last checked: 2026-10-02
- Also known as: boxed warning CAR-T; T cell lymphoma after CAR-T; secondary primary malignancy after CAR T; CAR-positive lymphoma
- Tags: rejuvenation; survivorship; transplant; cell-therapy; second-cancer
- Principle: An integrating lentiviral or gammaretroviral vector inserts semi-randomly into the genome of the transduced T cell and can, in principle, disrupt a tumour suppressor or activate an oncogene. That hazard is why integrating vectors carry the longest regulatory follow-up requirement. Against it, the transduced population is a terminally differentiated, antigen-experienced T cell pool rather than a self-renewing stem cell pool, which limits the opportunity for a transformed clone to expand, and the recipients already carry clonal haematopoiesis and therapy-selected T-cell clones from prior treatment, which is the commoner explanation for the lymphomas actually observed.
- Since: 2024
- Strengths: The regulatory response is public and specific, including the requirement to test new tumours for the CAR transgene; Published incidence estimates converge on a very low figure, approximately 0.03 to 0.3 per cent; Most characterised cases show no evidence of vector-driven transformation; Lifelong monitoring for second cancers is now explicit on every approved product's label
- Limitations: The FDA action states no incidence, so the label alone does not quantify the risk; At least one case with a CAR integration in TP53 confirms vector-driven transformation is possible; Follow-up of commercial CAR-T cohorts is still short relative to the latency of second cancers; Second primary malignancies of all kinds after CAR-T are substantially commoner than T-cell lymphoma, and separating treatment effect from prior-therapy effect is not possible in these cohorts

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Chimeric_antigen_receptor_T_cell
- FDA: FDA requires boxed warning for T cell malignancies following treatment with BCMA-directed or CD19-directed autologous CAR T cell immunotherapies (18 April 2024): https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/fda-requires-boxed-warning-t-cell-malignancies-following-treatment-bcma-directed-or-cd19-directed
- Verdun and Marks, Secondary cancers after chimeric antigen receptor T-cell therapy (NEJM 2024): https://doi.org/10.1056/NEJMp2400209
- Ghilardi et al., T cell lymphoma and secondary primary malignancy risk after commercial CAR T cell therapy (Nat Med 2024): https://doi.org/10.1038/s41591-024-02826-w
- Stella et al., T-cell lymphoma following chimeric antigen receptor-T therapy: a cause for concern? (Haematologica 2026): https://doi.org/10.3324/haematol.2026.301592
- Perica et al., CD4+ T-cell lymphoma harboring a chimeric antigen receptor integration in TP53 (NEJM 2025): https://doi.org/10.1056/NEJMoa2411507

## Connected records

- technologies: [After a transplant or cell therapy: what to ask for](https://onco.cc/technologies/rejuv-tx-what-to-ask-for/), [Blood counts that do not come back after CAR-T: ICAHT](https://onco.cc/technologies/rejuv-tx-prolonged-cytopenias/), [CAR-T cell therapy](https://onco.cc/technologies/car-t/), [Clonal haematopoiesis after cancer treatment](https://onco.cc/technologies/rejuv-age-clonal-haematopoiesis-after-therapy/), [ICANS, and whether thinking recovers after CAR-T](https://onco.cc/technologies/rejuv-tx-icans-and-neurocognition/), [Long-term follow-up for gene-modified cell products: fifteen years, and why](https://onco.cc/technologies/rejuv-tx-gene-modified-follow-up/), [Second cancers after allogeneic transplant](https://onco.cc/technologies/rejuv-tx-second-cancers/)
- fronts: [Recovery & Rejuvenation](https://onco.cc/fronts/rejuvenation/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- terms: [Late effects and survivorship toxicity](https://onco.cc/terms/late-effects/), [Secondary malignancy (therapy-related cancer)](https://onco.cc/terms/secondary-malignancy/)
- bottlenecks: [Survivorship and late effects are neglected](https://onco.cc/bottlenecks/b-survivorship/), [The newest treatments have not existed long enough for their late effects to appear](https://onco.cc/bottlenecks/rejuv-agenda-latency-outruns-the-evidence/), [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/)
- ideas: [Enrol every new systemic therapy into a registry linkage that will still report in thirty years](https://onco.cc/ideas/idea-rejuv-second-cancer-latency-cohort-for-new-drugs/)

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