** Shares in Belgian biotech company Argenx rise 4%, with KBC analysts saying its Vyvgart drug is still the top contender despite positive trial data from a competitor

** Amgen on Tuesday reported favourable phase 3 data for its Uplizna drug in treating rare muscle-weakening disease myasthenia gravis

** "We deem the Uplizna dataset to be strong yet somewhat less compelling than Vyvgart," KBC says

** "Vyvgart has shown strong effects already at week 4, and thereby oversteps the efficacy of Uplizna at week 26," KBC adds

** The shares are on track for their best day since Aug. 9 if the gains hold, topping Belgium's blue-chip BEL 20 index

** Including Wednesday's rise, they have gained 42% YTD​

(Reporting by Dimitri Rhodes)

((Dimitri.Rhodes@thomsonreuters.com))