Merck's Keytruda rides breast cancer hot streak to frontline chemo-combo win

Keytruda
Merck & Co.'s Keytruda has now come up positive in two straight TNBC studies. (Merck)

Merck & Co.’s Keytruda may have stumbled early in its candidacy as a triple-negative breast cancer treatment, but those days seem to be behind it.

The immuno-oncology star, in tandem with chemo, topped solo chemo at staving off disease progression in patients with certain levels of biomarker PD-L1—specifically, those with a combined positive score of 10 or greater.

Full results from the trial, called Keynote-355, won’t be available until a future medical meeting—RBC Capital Markets analyst Randall Stanicky has his money on ASCO, he wrote in a Wednesday morning note to clients—but in the meantime, the New Jersey drugmaker intends to discuss them with regulators. The trial will also continue to see whether Keytruda can hit its other primary endpoint by showing it can lengthen patients’ lives.

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

One thing's for sure: Investors will be waiting eagerly to compare Merck's data set with Roche's from the same setting. The Swiss drugmaker was the first immuno-oncology company to score a TNBC nod, with the FDA approving its checkpoint inhibitor Tecentriq last March in PD-L1 positive patients. 

As Evercore ISI analyst Umer Raffat pointed out in an investor note, Merck's trial "allowed a wider range of chemo" options than Roche's did, so if it can win an approval, it would "allow docs more flexibility, which could be a commercial advantage."

But Leerink Partners' Daina Graybosch was less upbeat. "We think Merck may struggle to gain a foothold for Keytruda in metastatic triple-negative breast cancer," she wrote in her own investor note, pointing out that "by the time Merck enters the market, Roche will have a two-year lead, in addition to a more predictive biomarker for clinical benefit (immune-cell (IC) PD-L1)." 

RELATED: ESMO: Merck's Keytruda posts first-in-class victory in pre-surgery breast cancer

The Keynote-355 results extend a positive streak for Keytruda in TNBC, an aggressive, tough-to-treat form of breast cancer. Back in September, the pharma giant revealed that among pre-surgery patients, a Keytruda-chemo combo beat chemo alone at clearing all signs of cancer from breast and lymph node tissue by the time of surgery, doing so in 64.8% of patients.

And the way Stanicky sees it, Merck’s Wednesday update “should de-risk” that neoadjuvant study, called Keynote-522, he wrote.

But things didn’t start out so well for Keytruda in the TNBC arena. Last May, study results showed the drug had failed to extend the lives of previously treated patients.

Of course, there were some key differences between that trial and the two that have now read out positively: It tested the drug solo, instead of with chemo, and in a later line of treatment. It also used only overall survival as a primary endpoint.

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