Atara Biotherapeutics sinks as FDA rejects cancer drug application

Shares of drugmaker Atara Biotherapeutics ATRA.O fall 49% to $6.91 premarket

Co says U.S. FDA has rejected its application to market Ebvallo, a treatment for a rare and aggressive cancer linked to the Epstein-Barr virus in patients who have received organ transplants

FDA said main trial was insufficient to prove effectiveness; had earlier indicated single-arm trial was acceptable - ATRA

No safety or manufacturing concerns raised, co says; plans meeting with FDA to discuss next steps

Epstein-Barr virus is a common virus that can cause infections and, in rare cases, lead to certain cancers

As of last close, stock up ~36% over the past year