(Reuters) -The U.S. Food and Drug Administration's staff reviewers on Wednesday raised safety concerns over the use of Johnson & Johnson's and Bristol Myers Squibb's cancer therapies as earlier treatments for blood cancer patients.

Staff reviewers said that the pattern of early deaths observed in patients treated with both the therapies in their respective trials raised uncertainty about the treatments' overall survival benefit in patients.

The therapies - J&J's Carvykti and Bristol Myers' Abecma - are approved by the FDA to treat patients with multiple myeloma who have received at least four prior lines of treatment.

The FDA staff said that data for J&J's Carvykti was unclear to establish a favorable benefit-risk profile of the treatment.

Data analysis provided by Bristol Myers did not provide "convincing evidence" that treatment with Abecma helps patients extend the time they live after receiving treatment or a benefit of overall survival.

The comments were made in briefing documents prepared ahead of a meeting of the FDA's independent advisers on Friday, which is being closely watched by investors to understand the regulator's view on CAR-T therapies after recent scrutiny into the treatments.

(Reporting by Sneha S K and Bhanvi Satija in Bengaluru; Editing by Shailesh Kuber)