Merck's Top Cancer Therapy Takes Another Big Leap Forward

Breast cancer patients with particularly aggressive tumor profiles were treated to some good news on Thursday. Clinical trial results from Merck (NYSE: MRK) showed that adding Keytruda to standard chemotherapy reduced those patients' risk of disease progression in the first-line treatment setting.

Targeted cancer therapies work well for breast cancer patients with tumors that test positive for estrogen receptor, progesterone receptor, or human epidermal growth factor receptor 2 (HER2). Unfortunately, around 15% to 20% of all breast cancer patients have tumors that don't express any of those targets -- thus their designation as "triple-negative" breast cancers. Merck's Keynote-355 trial tested Keytruda as a treatment for triple-negative breast cancer (TNBC) patients who have significant amounts of programmed death-ligand 1 (PD-L1) on their tumors, and the results of the study are compelling.

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Source Fool.com