(Reuters) -GSK shares fell more than 6% on Friday to the bottom of Britain's blue-chip index after a U.S. FDA advisory panel recommended against approving its blood cancer drug Blenrep, citing earlier concerns over side effects.

The British drugmaker was trying to revive the drug, which was pulled from U.S. markets in 2022 after failing a late-stage study. Its shares fell as much as 7% to 1,315 pence by 0807 GMT, compared with a 0.2% rise in the FTSE 100 index.

GSK's renewed application is based on two late-stage trials showing that combination therapies with Blenrep helped reduce the risk of death and delayed cancer progression.

The setback comes at a time when GSK is banking on a boost from newer drug approvals to help offset declining sales from top drugs and vaccines. It is also bracing for patent expirations in its HIV portfolio from 2028.

The FDA is due to give a formal decision on Blenrep next week, but analysts at Berenberg, JPMorgan and Barclays said the regulator is unlikely to approve the therapy.

The FDA typically follows the advice of its advisory panels, though it is not bound to do so.

GSK has set a long-term target of reaching more than 40 billion pounds ($53.7 billion) in overall sales by 2031, with peak annual sales for Blenrep at over 3 billion pounds.

JPMorgan analysts said GSK will have to lower its target for the drug's sales, as the U.S. was expected to be its biggest market, as well as revise the 2031 goal.

"GSK remains confident in the benefit/risk profile of Blenrep and will continue to work closely with the FDA as they complete their review for Blenrep," the drugmaker had said in a statement on Thursday.

Its second-quarter earnings report is due on July 30.

The side effects cited by the FDA advisory panel included blurred vision, photophobia and dry eyes. It also flagged concerns around the dosing regimen and lack of U.S. patient representation in the trials.

($1 = 0.7446 pounds)

(Reporting by Unnamalai L and Pushkala Aripaka in Bengaluru; Editing by Nivedita Bhattacharjee and Mrigank Dhaniwala)