Shares of Kite Pharma (KITE) fell Monday due to the death of a cancer patient from brain swelling following treatment with the company's CAR-T therapy KTE-C19.

The patient death in a KTE-C19 safety study occurred in April. The FDA was notified but the study was not placed on any clinical hold, Kite said on a Monday morning conference call.

Still, the death rattled investors because death from brain swelling, or cerebral edema, is the same severe toxic event that scuttled a competing CAR-T therapy from Juno Therapeutics (JUNO) .

Kite shares are down 11% to $73.10 in Monday trading.

Until Monday's disclosure, Kite's KTE-C19 development program had not recorded a death due to cerebral edema. The FDA is currently reviewing an application submitted by Kite to approve KTE-C19 for patients with advanced non-Hodgkin lymphoma.

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On its Monday call, Kite Chief Medical Officer David Chang said the patient who died had refractory non-Hodgkin lymphoma described as "explosive" and "rapidly progressing" before treatment with KTE-C19. Within two days, the patient's neurological condition deteriorated quickly, leading to death, Chang said.

CAR-T is a new form of cancer immunotherapy in which a patient's own T cells are removed and then engineered to identify and kill malignant blood cancer cells. CAR-T is highly effective at eliminating cancer cells in patients no longer responsive to previous treatments but it's also risky. CAR-Ts are known to cause a dangerous, immune system-related toxicity known as cytokine release syndrome.

Juno Therapeutics was forced to discontinue development of JCAR015 following the deaths of five patients due to cerebral edema.

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