The U.S. Food and Drug Administration's staff reviewers on Tuesday raised safety concerns that GSK's blood cancer drug Blenrep, when used in combination with other treatments, may cause eye damage in patients.

In briefing documents released on the health regulator's website, staff reviewers said the benefit-risk profile of Blenrep remains unclear, citing concerns about safety, tolerability and appropriate dosages.

The drug causes ocular toxicity that represents "unique toxicity not seen with any currently available treatments for multiple myeloma," staff reviewers said.

The FDA staff's assessment comes ahead of a meeting of its independent experts on Thursday.