** Shares of drug developer Replimune Group REPL.O fall 76.5% to $2.90 premarket

** Co says the U.S. FDA declined to approve its experimental skin cancer drug, called RP1, for patients with advanced melanoma

** The FDA, in its so-called complete response letter, said the clinical trial to test the drug "was not considered to be an adequate and well-controlled clinical investigation that provides substantial evidence of effectiveness"

** FDA said the trial cannot be adequately interpreted due to the heterogeneity of the patient population - REPL

** Co plans to urgently interact with the FDA to find a path forward

** Co was testing RP1 in combination with Bristol Myers Squibb's BMY.N Opdivo in patients with advanced skin cancer

** Up to last close, REPL up 1.8% YTD

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com))