Roth Capital analyst Tony Butler said he is optimistic about the efficacy and safety profile of ARQ 531 following the company's presentation of trial data, investor call and his talk with management. However, he thinks the key uncertainty now is durability of responses, which he highlights as important given the refractory population and the fact that ibrutinib was also based on survival data. He has raised his view of the probability of success for ARQ 531 to 50% from 33% previously and increased his price target to $13 on ArQule shares, on which he keeps Buy rating.