The Cancer “Breakthrough” That Led to 3X More Deaths
Cancer patients were told this drug represented the future.
It received accelerated FDA approval.
Doctors prescribed it.
Investors poured in money.
And for a while, everything looked promising.
The drug appeared to control cancer better than standard treatment.
Tumors shrank.
Disease progression slowed.
The headlines practically wrote themselves.
Then the follow-up research arrived.
And what researchers found should make every patient stop and think twice about how cancer drugs are approved.
Because the “breakthrough” treatment ended up being linked to three times as many deaths as other therapies.
The drug is called Zynlonta.
It was granted accelerated FDA approval in 2021 for a difficult-to-treat form of blood cancer called diffuse large B-cell lymphoma.
Accelerated approval allows drugs to reach patients before definitive proof that they help people live longer.
The FDA essentially says: “The early results look promising. We’ll allow approval now, but you must prove the benefit later.”
That’s where confirmatory trials come in. And that’s exactly what just happened.
Researchers enrolled 440 lymphoma patients in a large Phase 3 study designed to verify whether Zynlonta truly delivered meaningful benefits. The results were anything but straightforward.
On paper, the drug appeared successful.
Patients receiving Zynlonta experienced a 27% reduction in the risk of cancer progression or death. Their cancer remained under control for a median of 6.1 months compared to 4.7 months in the control group. Complete response rates were also higher.
Sounds like a victory, right?
Not so fast.
Researchers also reported 27 deaths among patients receiving Zynlonta compared to just 9 deaths in the control group.
That’s a death rate of 13.2% versus 4.6%—nearly three times higher. Serious adverse events were also substantially more common.
Most of the deaths occurred in patients age 75 and older.
We’ve written before that medicine often focuses on what are called “surrogate endpoints.”
Tumors shrink. Blood markers improve. Scans look better.
Yet patients don’t necessarily live longer—or live better.
That’s why survival remains the gold standard.
After all, nobody takes cancer treatment because they want a prettier scan. They take it because they want more healthy years with their families.
This latest result is a powerful reminder that shrinking tumors and delaying progression are not always the same thing as improving survival.
And it’s exactly why confirmatory trials matter.
Accelerated approval can help get promising therapies to patients faster. But sometimes the final data reveal a much more complicated story than the early headlines suggested.
When it comes to cancer treatment, the question isn’t whether a drug can shrink a tumor.
The question is whether it helps patients live longer, better lives.
And sometimes those are two very different things.
To asking the tough questions,
Ray Thatcher
Research Director, Health Sciences Institute
Sources:
Manalac, T. (2026, June 4). ADC Therapeutics nosedives on 27 deaths in confirmatory trial for lymphoma drug. BioSpace. https://www.biospace.com/drug-development/adc-therapeutics-nosedives-on-27-deaths-in-confirmatory-trial-for-lymphoma-drug
Dunleavy, K. (2026, June 4). ADC Therapeutics’ shares plummet after patient deaths in trial of Zynlonta. Fierce Pharma. https://www.fiercepharma.com/pharma/adcs-shares-plummet-after-patient-deaths-trial-zynlonta?utm_source=chatgpt.com
