On Thursday, Roche announced that IMpassion131, their phase III evaluating the combination of atezo plus paclitaxel, failed to hits its primary PFS endpoint in previously untreated patients with PD-L1+ metastatic triple-negative breast cancer (TNBC). But wait, you ask. Didn’t they already get approved in that indication? Isn’t it the standard of care? And on Wednesday, the answer was yes; today, it’s more like, Kind of. Because the approval specified nab-paclitaxel (Abraxane). IMpassion131 tested solvent-bound paclitaxel, better known as Taxol. This result is a reminder that these drugs aren’t necessarily interchangeable.

Atezo + Abraxane was granted an accelerated approval in PD-L1+ TNBC, and I would say up front that I don’t think this result creates any risk with the FDA, though label expansion may turn out to be an issue. But there’s a lot about this update that’s intriguing, particularly as it relates to Abraxane and the implications for the next and newest study in the TNBC series, IMpassion132. For patients with TNBC, the news changes the narrative from atezo as a break-from-the-pack wonder drug to its role in a combo and the importance of the chemo backbone.