** Abbisko Cayman 2256.HK jumps 9.5% to HK$6.92, highest since June 2022
** Stock set for biggest one-day pct rise since February 20
** Chinese oncology therapies developer says it will buy back shares on-market for up to HK$200 mln ($25.73 mln), reflecting management's confidence in firm's operational growth outlook, financial position
** Stock up 48.7% YTD
($1 = HK$7.7743)
(Reporting by Donny Kwok)
((donny.kwok@thomsonreuters.com))