BARCELONA—Merck’s Keytruda may have come up short in metastatic triple negative breast cancer over the weekend, but in the pre- and post-surgery settings, it posted a first-of its-kind win.
Among pre-surgery patients, the combination of Keytruda and chemo beat out solo chemo at spurring pathological complete responses—meaning their breast and lymph node tissue showed no signs of residual cancer at surgery. 64.8% of patients receiving Keytruda hit that benchmark, compared with 51.2% of chemo-only patients.
And patients saw that benefit regardless of their levels of biomarker PD-L1, Merck said Sunday at the European Society for Medical Oncology annual meeting.
That’s an important victory, given that “pathologic complete response is a good predictor of long-term outcomes,” Roy Baynes, M.D., Merck SVP and head of global clinical development, said.
“If a patient who presents with a triple-negative breast mass is treated with a neoadjuvant therapy and achieves a pathological complete response, that person is likely to do well,” he said.
The study, dubbed Keynote-522, had another endpoint, too, looking at Keytruda’s ability to cut the risk of disease recurrence and progression after surgery. Patients who received the drug before surgery went on to receive it afterward, while those on only chemo got placebo.
At a median 15.5 months after treatment—an early interim look-in—Keytruda had slashed the risk of recurrence in the adjuvant setting by 37% compared with the chemo-placebo regimen. And while that benefit isn’t statistically significant, “it does give us a lot of encouragement” about the future of the trial, Baynes said.
“At this moment in time that does not cross a statistical boundary, but the bar was very high because it’s very early in this trial,” he added.
The data were enough to convince U.S. regulators to bestow Keytruda with their breakthrough therapy designation, speeding its path toward approval.
Unfortunately for Merck, its immuno-oncology standout hasn’t so far seen the same success in the metastatic TNBC arena. Saturday at ESMO, the company presented detailed results from a trial in which Keytruda monotherapy failed to extend survival in previously treated patients.