What happened

Shares of Kite Pharma Inc. (NASDAQ: KITE), a biotech developing cell therapies for the treatment of cancer, are getting beaten up after the company revealed a patient death associated with its lead candidate. As of 10:50 a.m. EDT on Monday, the stock had retreated 11.9% in response to the disclosure.

So what 

Kite Pharma is one of a handful of companies racing to develop the first CAR-T therapy, a form of treatment that involves removing and then modifying a patient's own immune cells to recognize and attack cancer cells. Sadly, this type of treatment can be a little too effective, which in turn can lead to fatal brain swelling.

A frustrated man face down on a table in front of a chart with a red arrow pointing down

Image source: Getty Images.

Before today, Kite Pharma was the clear leader with axicabtagene ciloleucel, formerly KTE-C19 (or axi-cel). It gained the pole position after several patient deaths derailed Juno Therapeutics and its former lead CAR-T candidate last year.

The patient death is especially surprising because it occurred within a safety expansion cohort the company added to the study supporting its application. Thirty patients were enrolled to evaluate a potential strategy to mitigate effects of cytokine release syndrome (CRS) that arise when therapies such as axi-cel destroy too many cancer cells too quickly. Two of the patients developed serious CRS, one of whom also experienced multiple organ failures and brain swelling that led to death.

Now what

The event was deemed related to the therapy, but the patient may have been extremely frail to begin with. According to Kite's disclosure, the patient hadn't responded to standard treatments prior to receiving axi-cel and displayed symptoms of rapid disease progression. It's important to remember that no matter how dire a patient's situation is at the start of a trial, the Food and Drug Administration takes any patient death during treatment extremely seriously.

Kite Pharma had treated more than 200 patients with axi-cel without any cases of fatal brain swelling, and trial data so far strongly suggests the breakthrough therapy is highly effective among patients who currently lack treatment options. Although investors probably don't need to worry about the FDA rejecting the entire axi-cel application in response to a single patient death, it might ask for more safety information before continuing the review process. Investors might want to brace themselves for a longer-than-anticipated review process.