MADRID, Spain—Right now, Merck’s Keytruda is the only PD-1/PD-L1 med with data to show it can improve overall survival in the second-line bladder cancer setting. And it keeps piling it on.

Over the weekend at the European Society for Medical Oncology (ESMO) annual meeting in Madrid, the New Jersey drugmaker touted mature results from a phase 3 trial showing that in patients whose disease had progressed following platinum chemo treatment, Keytruda continued to demonstrate an overall survival advantage over chemo at a median follow-up of 22.5 months.

The med reduced the risk of death by 30%, posting an overall survival advantage of 10.3 months versus chemo's 7.4 months. The 18-month overall survival rate was 33.2% for the Keytruda arm, compared with 19.7% for the chemo arm, Merck said.

That Keytruda benefit came regardless of patients' PD-L1 expression levels; in patients whose tumors expressed PD-L1, though, the death-risk reduction was even greater, measuring 42%.

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Merck wasn’t the first med in its class to snag a bladder cancer go-ahead from the FDA; that distinction belongs to Roche’s Tecentriq, which won approval in May of 2016. Next came Bristol-Myers Squibb’s Opdivo, and the remaining agents—AstraZeneca’s Imfinzi, Pfizer and Merck KGaA’s Bavencio and Keytruda—rounded out the pack with green lights this May.

RELATED: Roche’s shocking Tecentriq fail raises red flag for bladder cancer rivals

Keytruda, though, is the only one of the lot with overall survival data to back up its case, and it’s not for lack of trying from its rivals. In May, Tecentriq flopped its second-line bladder cancer trial, throwing its regulatory status into question and raising red flags around its fellow PD-L1 meds.

Roche, for its part, faults a surprisingly good performance from chemo med vinflunine for the failure, Roche global head of clinical development in hematology and oncology Dietmar Berger said in an interview at June’s American Society of Clinical Oncology (ASCO) annual meeting.

"If you look at the study, the Tecentriq arm performed exactly as it did" in phase 2, he said, and it was also "very much in line with many of the data that we see from other checkpoint inhibitors."

Merck’s head of global clinical development Roy Baynes, though, put Keytruda’s survival data into context in a separate ASCO interview, trumpeting it as an advantage for the pharma giant. "I’m not the commercial guy—I can’t tell you what the commercial performance will look like. But I can tell you as a practicing oncologist, if I have the choice of a drug that had established a survival benefit and a group of drugs that hadn’t, I would probably go with that which had a survival benefit," he said.