Merck & Co.'s Keytruda hits main goal of triple-negative breast cancer study

Merck & Co. on Wednesday said results from an interim analysis of the Phase III KEYNOTE-355 trial showed that adding Keytruda (pembrolizumab) to chemotherapy significantly prolonged progression-free survival (PFS), one of the study's dual primary endpoints, versus chemotherapy alone in first-line patients with metastatic triple-negative breast cancer (TNBC) whose tumours express PD-L1 with a combined positive score (CPS) of at least 10. Roger Perlmutter, president of Merck Research Laboratories, remarked "we look forward to sharing these findings with the medical community at an upcoming congress and discussing them with the FDA and other regulatory authorities."

The two-part trial is comparing Keytruda in combination with one of three different chemotherapies, to placebo plus one of the three chemotherapy regimens, in patients with locally recurrent, inoperable or metastatic TNBC that has not been previously treated with chemotherapy in the metastatic setting. The second part of KEYNOTE-355 enrolled 847 patients and has co-primary goals of PFS and overall survival (OS), which are being assessed in the overall study population, as well as in patient subgroups whose tumours express PD-L1 with a CPS of at least 1 or a CPS of at least 10. Secondary endpoints of the study include objective response rate, duration of response and disease control rate.

Perlmutter said "it is very encouraging that Keytruda in combination with chemotherapy has now demonstrated positive results as both a first-line treatment in the metastatic setting with this trial, and as neoadjuvant therapy in the KEYNOTE-522 trial," where the pathological complete response rate for TNBC patients was 64.8% when the anti-PD-1 therapy was added to chemotherapy, versus 51.2% for chemotherapy alone. For related analysis, see KOL Views Results: Keytruda's Keynote-522 data do not overwhelm, but still on a path towards approval for TNBC, says leading oncologist.

In addition to KEYNOTE-355 and KEYNOTE-522, Keytruda is also being evaluated in TNBC in the ongoing KEYNOTE-242 trial. Meanwhile, in May last year, Merck reported that Keytruda monotherapy failed to significantly extend OS in the Phase III KEYNOTE-119 study, versus chemotherapy alone, when used in the second- or third-line treatment of patients with metastatic TNBC.  

Roche's Tecentriq (atezolizumab), in combination with chemotherapy, became the first immunotherapy regimen to be approved in breast cancer when the FDA cleared use of the PD-L1 inhibitor last year in adults with PD-L1-positive unresectable, locally advanced or metastatic TNBC. Tecentriq is also authorised in this indication in Europe.

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