SAN ANTONIO—Merck & Co.'s Keytruda and Roche's Tecentriq are battling for immuno-oncology supremacy in an ever-growing range of indications. But in hard-to-treat triple-negative breast cancer (TNBC), Keytruda's latest data came out on top.

Adding Keytruda to standard-of-care chemotherapy ahead of surgery delivered pathologic complete responses—a lack of cancer cells in surgically removed tissue––in 64.8% of newly diagnosed TNBC patients whose disease had spread to the lymph nodes, a new subanalysis shows. Just 44.1% of those treated with chemo alone could say the same.

Drawn from Keytruda's phase 3 Keynote-522 study, the subgroup data were presented Thursday at the San Antonio Breast Cancer Symposium. They back up top-line numbers released in September showing a Keytruda-chemo combo achieved a pathologic complete response in 64.8% of the study's patients compared with 51.2% on chemo alone.

Overall, patients in the Keynote-522 study also showed a 37% risk reduction in disease recurrence after surgery compared with solo chemo, a result that wasn't statistically significant.

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

Roy Baynes, Merck's chief medical officer and head of global clinical development, said the results from the subdata readout were promising and generally supportive of the study's top-line findings. 

"At this relatively early stage of the trial readouts, the results look very encouraging," Baynes said.

While Keytruda didn't show a significant benefit over chemo in terms of preventing recurrence at this stage of the study, Baynes noted that achieving pathologic complete response was generally a "good predictor" that the disease wouldn't return. 

Merck's win is a blow to Roche's Tecentriq, which posted new data Thursday showing the anti-PD-L1 therapy given after chemotherapy didn't best chemotherapy alone in achieving pathologic complete response for TNBC patients. 

In patients treated with Tecentriq after chemo but before surgery, 43.5% saw no signs of cancer after surgery compared with 40.8% treated just with chemotherapy. The benefit was greater for patients whose tumors tested positive for the PD-L1 biomarker––51.9% for the combo versus 48% for solo chemo––but still not statistically significant. 

RELATED: NICE shoots down Roche's Tecentriq in tough-to-treat breast cancer

Those results will certainly sting Roche as its archival Keytruda bulldozes ahead and the Swiss drugmaker faces pushback from international regulators in the TNBC space. 

In October, England's National Institute for Health and Care Excellence (NICE) shot down a Tecentriq-Abraxane combo as a cost-effective option for TNBC on England’s National Health Service.

Despite acknowledging that the combo beat out a placebo-chemo combo at staving off disease progression by 2.5 months in patients whose tumors express biomarker PD-L1, NICE knocked Roche for scanty clinical data comparing the combo to other chemo meds, including weekly paclitaxel and docetaxel.

NICE’s rebuff will put the ball in Roche’s court to either supplement its data submission or consider offering a bigger discount. In a statement, Meindert Boysen, NICE’s director of the Centre for Health Technology Evaluation, said he expected U.K. patients would be disappointed by the results but pledged to continue working with Roche to reach a solution.