** Shares of cancer therapy maker Novocure NVCR.O down 21.6% at $14 in the pre-market trading

** Co's treatment for newly diagnosed brain tumors did not meet the main goal of a late-stage study

** Says the trial did not show an improvement in overall survival for patients whose treatment started early compared to those starting at the maintenance stage.

** Trial demonstrates durable survival benefit for patients in both arms of the trial with no new safety signals observed, co says

** As of last close, stock was up 38% YTD