** Shares of drug developer AnaptysBio ANAB.O tumble 14.5% to $32.21 premarket
** GSK's GSK.L oncology unit, Tesaro, sued AnaptysBio late Thursday, claiming the biotech breached a 2014 license deal for cancer drug Jemperli
** Tesaro wants to terminate the agreement, cut royalties by half, and secure permanent rights to Jemperli
** AnaptysBio countersued on Friday, accusing Tesaro of breaking exclusivity rules and favoring other GSK drugs over Jemperli
** Both sides have sought an expedited trial in Delaware, expected in July 2026
** In 2020, AnaptysBio sued GSK over similar exclusivity concerns
** Up to last close, stock up ~184% YTD
(Reporting by Sahil Pandey in Bengaluru)
((Sahil.Pandey@thomsonreuters.com))