Pfizer Ends Mid-Stage Trial for CD47 Blood Cancer Drug

Pfizer has discontinued its Phase 1b/2 trial of maplirpacept (PF-07901801), a CD47-blocking agent, in combination with tafasitamab and lenalidomide for relapsed or refractory diffuse large B-cell lymphoma (DLBCL) patients ineligible for stem cell transplantation. The trial, which began in August 2023, enrolled only six participants before being terminated due to recruitment challenges. Pfizer stated that the decision was not related to safety or efficacy concerns.

Maplirpacept, acquired through Pfizer's $2.3 billion purchase of Trillium Therapeutics in 2021, is designed to block CD47—a protein that cancer cells use to evade immune detection. Despite this setback, Pfizer continues to explore maplirpacept's potential in other blood cancers, including multiple myeloma and acute myelocytic leukemia, and is conducting a Phase 1/2 trial in combination with Roche’s Columvi for relapsed or refractory DLBCL.

The discontinuation adds to the challenges faced by CD47-targeting therapies. Earlier, Gilead Sciences halted development of its CD47 antibody, magrolimab, in blood cancers after observing an increased risk of death in a late-stage trial. Similarly, ALX Oncology terminated studies of its CD47 blocker, evorpacept, in leukemia and myelodysplastic syndrome due to insufficient efficacy.

Despite these hurdles, Pfizer remains committed to investigating maplirpacept's potential, particularly in combination therapies, as part of its broader oncology strategy.