Moderna extends slide as analysts question valuation after cancer vaccine data

** Shares of drugmaker Moderna MRNA.O fall 4.7% to $193.02 premarket, extending Thursday's slide

** The stock closed down 17.57% at $202.63 on Thursday, wiping about $17.2 billion off its market value after a months-long rally

** The company and partner Merck MRK.N published detailed data from the late-stage melanoma trial after the results were leaked on an oncology website

** The data showed the experimental vaccine intismeran plus Keytruda cut the risk of melanoma death or recurrence by 42% and the risk of the cancer's spread by 38%, compared with Keytruda alone

** Several Wall Street analysts said before the meeting that investors were looking for the combination to cut the risk of recurrence by 40% or more

** RBC analyst Luca Issi calls the data "clearly impressive" but says the benefit is numerically lower than seen in mid-stage study, and adds it continues to "struggle to justify a $81b valuation despite the pullback"

** Morningstar analysts say "share prices ran too far following the initial top-line announcement in August"

** As of Thursday's close, MRNA up 587% YTD, mainly because of its surge after the initial top-line announcement in August; the stock traded around $63 the day before that announcement