ADC Therapeutics Says FDA Raised Concerns on Zynlonta Trial

What happened

ADC Therapeutics SA, a commercial-stage drugmaker listed on the New York Stock Exchange under the ticker ADCT, said the US Food and Drug Administration raised substantial concerns about the benefit-risk profile of the LOTIS-5 confirmatory trial of its lymphoma drug Zynlonta, according to reports from pharmaphorum and Seeking Alpha.

The company said it is "assessing the best regulatory path forward" for Zynlonta and the LOTIS-5 data, pharmaphorum reported. Seeking Alpha characterized the same disclosure as the company "assessing LOTIS-5 regulatory path forward."

According to an account of the company's quarterly report carried by StockTitan, the FDA's concerns centered on an imbalance in Grade 5 treatment-emergent adverse events — deaths during the trial attributed to treatment — along with limited data. Tracked coverage on Simply Wall St. attributes the shares' weakness to concerns about Zynlonta's risk-benefit profile and added regulatory risk following the LOTIS-5 results.

The disclosure accompanied the company's second quarter 2026 financial results, which ADC Therapeutics reported on August 13, 2026, according to a press release distributed by PR Newswire. On the accompanying earnings call, the company reported a cash balance of $219.1 million, which it said provides a runway at least into 2028, according to a transcript summary published by Yahoo Finance.

The stock closed at $1.22 on the event date, down 6.15% from the prior close of $1.30, according to price data.

Posts on X, including from accounts @NShkol92186 and @MarcJacksonLA, described the FDA concerns and referred to a filing and a roughly 12% decline in the shares. Those specific figures and characterizations come from anonymous social media accounts and could not be verified against a primary source, so they are reported here as unconfirmed.

What is Zynlonta and what is LOTIS-5

Zynlonta is ADC Therapeutics' approved treatment for certain lymphomas. It belongs to a class of medicines called antibody-drug conjugates: an antibody that seeks out a marker on cancer cells is chemically linked to a potent cell-killing payload, so the toxic drug is delivered preferentially to the tumor rather than to the whole body.

The FDA's initial approval of a cancer drug is frequently granted on the basis of earlier-stage or single-arm data, on the condition that the company run a further, larger trial afterward to confirm that the drug actually helps patients. That follow-up is called a confirmatory trial, and LOTIS-5 is the confirmatory trial for Zynlonta in its approved setting.

Confirmatory trials are not a formality. If the confirmatory data do not hold up, the FDA can require labeling changes, restrict the patient population the drug may be used in, or in the most serious cases seek to withdraw the approval. A "regulatory path forward" is the industry phrase for the company's decision about what submission to make next — a revised label, additional analyses, a new study, or a withdrawal.

What this means

The specific worry the FDA is described as having is an imbalance in Grade 5 treatment-emergent adverse events. In trial reporting, an adverse event is "treatment-emergent" if it appeared or worsened after the patient started the study drug, and Grade 5 is the top of the severity scale: it means the patient died. An "imbalance" means deaths were concentrated on one side of the comparison — here, the side being scrutinized — in a way the FDA considers a possible signal that the drug, or the way it is being used, contributed to them.

Grade 5 imbalances are treated seriously in oncology trials because the patients enrolled are already very sick, so investigators have to disentangle deaths caused by the disease from deaths caused by the treatment. When that separation is unclear, the FDA's judgment about whether the drug's benefit justifies its risk — the benefit-risk profile — becomes harder to support.

The second element the reports mention is limited data, which compounds the first. If a confirmatory trial yields a small amount of usable evidence, the agency has less to weigh against a safety signal.

For ADC Therapeutics this matters because the company is not a large, diversified drugmaker with other products absorbing the blow. Its disclosure states it is evaluating what to do next, and neither the FDA nor the company has announced a decision. What normally happens after a company says it is assessing a regulatory path is a period of internal analysis followed by an announcement — a further submission, a meeting with the agency, a new trial, or a label change — but nothing here establishes which of those will occur, and no timeline has been given.

The $219.1 million cash balance and the runway the company says it provides at least into 2028 are separate from the regulatory question and do not answer it. A cash runway describes how long the company can fund its operations at its current spending rate; it says nothing about whether a drug keeps its approval or its label.