ADC Therapeutics has announced voluntary pause of new patient enrolment in its Phase II LOTIS-9 trial of ZYNLONTA (loncastuximab tesirine-lpyl) and rituximab (Lonca-R) for the treatment of unfit or frail patients with previously untreated diffuse large B-cell lymphoma (DLBCL).

The decision to pause enrolment is based on the observations of potentially excessive respiratory-related events after consulting with the Data Monitoring Committee (DMC).

Out of the 40 patients enrolled, seven had Grade 5 fatal treatment-emergent adverse events (TEAEs) while five reported Grade 3 or Grade 4 respiratory-related TEAEs.

Six of the seven Grade 5 fatal events were assessed by the investigator and were claimed to be unrelated to the study drug.

The patients who died were greater than or equal to 80 years of age and had one or more significant active underlying respiratory and cardiac co-morbidities.

Grade 3 or Grade 4 respiratory-related TEAEs were resolved in four out of the five patients, and they completed the treatment protocol.

ADC Therapeutics CEO Ameet Mallik said: “Our top priority is the safety of every patient who participates in our clinical trials.

“Given the aggregate of the respiratory-related events seen in the trial, we implemented a voluntary pause of enrolment to allow for a thorough investigation of the data set.

“This trial includes a very difficult-to-treat patient population, with limited treatment options, and we will provide an update on next steps when available.”

The company also notified the US Food and Drug Administration, the European Medicines Agency, and all study investigators about the decision to pause enrolment.

ADC Therapeutics claimed that it will not be able to report additional data from the trial by the end of this year.