ESMO: Merck learns from Keytruda's monotherapy miss in triple-negative breast cancer

Merck's Keytruda failed a phase 3 monotherapy trial in a tough-to-treat form of breast cancer. (Merck)

BARCELONA—It’s official: Merck won’t be stepping on Roche’s toes anytime soon when it comes to metastatic triple negative breast cancer. But from its failed phase 3 trial, the New Jersey drugmaker did take away some important findings, execs say.

Saturday at the European Society for Medical Oncology annual meeting, the pharma giant presented data showing that in a study of previously treated TNBC patients, positive effects of treatment with Merck immuno-oncology star Keytruda increased as patients’ levels of biomarker PD-L1 increased.

Pitted against chemo, the drug cut patients’ risk of death by 3% in the all-comer population, by 14% in a group of patients with low levels of PD-L1, and by 22% in a group of patients whose levels were higher. “There was a progressive step up in improvement with each” step up in PD-L1, Roy Baynes, M.D., Merck SVP and head of global clinical development, said.

RELATED: Merck's powerhouse Keytruda whiffs breast cancer trial, delaying hopes for new use

The thing is, none of Keytruda’s effects hit the statistical significance threshold. And the drug didn’t fend off disease progression, either.

“The outcome was not what we hoped for, but we learned a lot from it and clearly there is a PD-L1 enrichment effect for monotherapy in these advanced patients,” Baynes said.

He added that pitting monotherapy against a standard-of-care therapy is “always a high bar” and that the data from the trial, dubbed Keynote-119, would be “useful in terms of how we think about the rest of the triple negative program.”

RELATED: Roche's I-O drug Tecentriq picks up key first-in-class breast cancer nod

Merck was hoping to join Roche in what’s currently an exclusive club for members of the PD-1/PD-L1 class. In March, the Swiss drugmaker snagged an FDA go-ahead for Keytruda rival Tecentriq, in combination with Celgene’s Abraxane, in first-line TNBC, thanks to data presented at last year’s ESMO conference showing the duo could cut the risk of disease worsening or death by 20%.

Of course, that nod for Roche was for newly diagnosed patients, rather than the previously treated group that Keynote-119 enrolled. But still, Tecentriq remains the only immunotherapy with any OK in the tough-to-treat disease area, and thanks to Merck’s miss, it could stay that way for a while.

That's not to say that Merck isn't trialling Keytruda for other TNBC indications. Its Keynote-355 study is looking at a Keytruda-chemo combo in previously untreated patients, and Sunday at ESMO, the company presented positive data from a study examining the drug in the adjuvant and neoadjuvant settings.