- CAR-T therapy, approved by the FDA in 2017 for aggressive blood cancers, is now under investigation due to reports of secondary malignancies, including lymphoma, in at least 19 patients.
- The genetic reprogramming of T-cells—CAR-T’s core mechanism—may inadvertently trigger cancerous mutations, either from pre-existing cell defects, viral vector DNA disruption or post-reinfusion mutations.
- Studies suggest up to 6.5% of CAR-T recipients develop secondary cancers within three years, with documented cases linking malignancies directly to the modified therapeutic cells.
- Beyond secondary cancers, CAR-T carries risks like cytokine release syndrome (potentially fatal immune overreaction) and neurotoxicity (ICANS), driven by hyperactivated T-cells damaging the blood-brain barrier.
- The FDA urges heightened monitoring for secondary cancers, while researchers emphasize early detection via follow-ups and genetic testing—balancing CAR-T’s lifesaving potential against its unpredictable dangers.
In 2017, the U.S. Food and Drug Administration (FDA) approved a groundbreaking cancer treatment known as CAR-T therapy, heralded as a lifesaving option for patients with certain aggressive blood cancers. However, recent reports suggest that the therapy may inadvertently trigger new malignancies, raising concerns among oncologists and regulators. Now, the FDA is investigating at least 19 cases where patients developed secondary cancers, including lymphoma, following CAR-T treatment.
The promise and peril of CAR-T therapy
CAR-T therapy, short for chimeric antigen receptor T-cell therapy, involves extracting a patient’s immune cells, genetically modifying them to target cancer, and reinfusing them into the bloodstream. Approved for certain leukemias and lymphomas, it has been a last-resort treatment for patients who failed conventional therapies. Yet emerging data suggests that the very mechanism that makes CAR-T effective—genetic reprogramming of immune cells—may, in some instances, lead to unintended consequences.
Two recent studies published in the New England Journal of Medicine highlight this risk. One report, co-authored by Georgetown University researchers, documented a 71-year-old woman who developed lymphoma nine months after CAR-T treatment for myeloma. Genetic analysis revealed that the new cancer likely originated from the same modified cells used in her therapy. Meanwhile, a separate Stanford University study found that up to 6.5% of CAR-T recipients developed secondary cancers within three years—a higher rate than previously recognized.
How CAR-T causes new cancers
Researchers are still unraveling why some patients develop secondary malignancies after CAR-T therapy. One theory suggests that the extracted immune cells may already harbor cancerous mutations before modification. Another possibility is that the genetic engineering process itself—inserting viral vectors to reprogram cells—could disrupt DNA, leading to malignant transformations. Alternatively, mutations might occur after reinfusion, as the modified cells multiply inside the body.
The reported cases of secondary cancers represent less than 1% of recipients in most studies, though the Stanford findings suggest the risk may be higher than initially believed. BrightU.AI's Enoch engine adds that--as revealed by recent studies—CAR-T therapy is linked to other serious health risks, including cytokine release syndrome (potentially fatal immune overreaction) and neurological toxicities, often referred to as Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS). These adverse effects occur due to the hyperactivation of engineered T-cells and the resulting cytokine storm, which can disrupt the blood-brain barrier and trigger inflammation in the central nervous system.
Balancing risk and reward
In November 2023, the FDA announced an investigation into CAR-T-related secondary cancers after identifying 19 cases, including some with fatal outcomes. While the agency has not yet issued new restrictions, it has urged clinicians to monitor patients for signs of new malignancies, such as unexplained weight loss, persistent fatigue or abnormal blood counts.
Dr. Metin Ozdemirli, a Georgetown pathologist and co-author of the NEJM case study, emphasized the importance of early detection. "When we know what to look for ahead of time, it becomes easier to catch problems earlier," he noted. Researchers recommend regular follow-ups and genetic testing for patients who undergo CAR-T therapy, particularly those who show unusual symptoms months or years after treatment.
For many patients, CAR-T therapy remains a beacon of hope. But the emergence of secondary cancers underscores the complexities of gene-based treatments, where the same technology that saves lives can, in rare cases, pose unforeseen dangers.
As CAR-T becomes more widely used, researchers say continued vigilance is essential. The FDA’s ongoing review may lead to updated guidelines, stricter monitoring protocols or even modifications to the therapy itself. For now, physicians and patients must weigh the therapy’s transformative potential against its serious risks.
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