I'm guessing that Sarissa converted most of the American Depositary Shares (ADS) they owned to common shares and that's why the Dec 2022 13F showed 19M reduction in ADS when compared to previous 13F. The Sarissa proxy shows that they have 20,300,000 common shares and 4,910,000 ADS. I don't think the common shares show up on the 13F because they are UK common shares. See link below for 13f securities.