Top Line: We already know ribociclib, just like the other CDK4/6 inhibitors, drastically improves progression-free survival as first- or second-line therapy for metastatic ER(+), HER2(-) breast cancer.
The Study: We know from initial reporting of the phase 3 MONALEESA-3 trial. Now we have final reporting, and you know what that means. Mature results on the secondary (but much more moving) endpoint of overall survival (OS). Remember, 726 women receiving fulvestrant were randomized 2:1 to the addition of ribo versus placebo. Now, it’s important to note the trial was designed with OS as a secondary endpoint mainly because power analysis estimated 351 deaths would be required to show a difference. And with ER(+) breast cancer, ain’t nobody got time for that. Well, at a median follow-up of over 3 years, 275 deaths have occurred—just over three-quarters of the estimated needed number. But the discrepancy in OS was already so large that...here we are. The rate of OS at 42 months was 58% with ribo versus 46% without. There’s nothing new to report with toxicity. Grade 3/4 events with ribo primarily consist of neutropenia (57%) and leukopenia (16%). 
TBL: Just like in MONALEESA-7, ribo again proves to significantly improve OS among women with metastatic ER(+), HER2(-) breast cancer...and that’s no easy feat. | Slamon, N Engl J med 2019


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