Allogene Therapeutics Inc. ALLO, -45.37% shares plunged in the extended session Thursday after the biotech drug developer said the Food and Drug Administration placed a hold on the company’s cancer drug clinical trials. Allogene shares, which had closed up 1.7% at $24.38 in the regular session, plunged as much as 40% after hours following a brief halt. Allogene said a single report of a “chromosomal abnormality” in a stage IV follicular lymphoma patient treated with the company’s ALLO-501A CAR T prompted the FDA put a hold on the drug’s study until an investigation is completed. “The company expects to provide additional updates in the coming weeks following consultation with the FDA,” Allogene said in a statement. “The FDA continues to actively review the end of Phase 1 materials submitted in anticipation for an ALLO-501A pivotal Phase 2 trial.”