Leerink analyst Geoffrey Porges says that one of the main reasons for the continued weakness of Alexion's (ALXN) stock has been the fear of competition for its Soliris in complement inhibition indications. However, after this year's European Hematology Association presentations by Alnylam (ALNY), RA Pharma, Achillion (ACHN), and Alexion itself, the analyst believes rivals to Alexion's complement inhibition market position are facing longer development paths, and more uncertainty, than investors understand. Leerink has an Outperform rating on Alexion's shares.