July 15 (Reuters) - 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 British drugmaker is seeking approval for Blenrep in combination with bortezomib

plus dexamethasone and pomalidomide plus dexamethasone for the treatment of patients with

multiple myeloma who have received at least previous therapy.

Both bortezomib and pomalidomide are established cancer therapies, while dexamethasone

is a widely used generic steroid drug.

The assessment comes ahead of an independent expert panel meeting on Thursday. The FDA is

set to decide on the drug next week.

The agency raised concerns of ocular toxicity such as blurred vision, photophobia, and dry

eye in patients receiving the combination treatment. Blenrep's initial approval already carried

a warning about ocular side effects.

The ocular toxicity observed "is a unique toxicity not seen with any currently available

treatments for multiple myeloma," staff reviewers said.

The agency noted that the dose adjustment protocols and ophthalmic monitoring schedules

implemented in the trials may be difficult to reproduce in routine clinical practice, raising

concerns about the drug's use outside tightly controlled study settings.

The panel will discuss whether appropriate dosages have been identified for proposed

patients and vote on whether the drug's overall benefit-risk profile in combination with other

treatments is favorable.

Blenrep belongs to a class of targeted cancer therapies called antibody drug conjugates

that work like "guided missiles," killing tumor cells while leaving healthy ones unharmed.