Where's that aducanumab filing, Biogen?

For many months, the science world thought aducanumab dead. Then, this fall, Biogen announced that it would resurrect the controversial Alzheimer’s drug — with plans to file for FDA approval in early 2020. Now, we’re on the cusp of February, and there’s no filing in sight. Rather, the company said in its earnings call yesterday that it planned to submit “as soon as possible” — which, as STAT’s Adam Feuerstein writes, is decidedly “squishy.”

Biogen’s chief medical officer pointed out to investors that it’s not particularly difficult, after all, to complete a filing at this point — just a “matter of putting together documentation.”

So what’s the holdup?