Many of those candidates have similar mechanism of action. 520 is different from any of them. This doesn't mean 520 will work out. If it does, even if all of other drug candidates work out, 520 can still have its place.
I'm not sure if rkrw is referring to potential MM drugs in the relapsed/refractory setting which is what ARRY is targeting for 520, and obviously not the front-line setting where Revlimid and Velcade are the mainstays. Even if he's referring to the relapsed/refractory setting, as you note, 520 is different from the competition. Also, 520 is synergistic with Velcade pre-clinically whereas carfilzomib, as an example, apparently competes directly with Velcade (#msg-55157672). All told, although I'm not exactly sold on 520, I don't share rkrw's extremely bearish view.
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