Key Takeaways Keytruda generated over half of Merck's pharma sales during the first half of 2025.Early-stage lung cancer and metastatic uptake are fueling strong sales momentum for Keytruda.FDA approval of subcutaneous Keytruda Qlex is likely to extend protection beyond 2028.Merck (MRK) holds a strong foothold in the oncology space, propelled by its blockbuster PD-L1 inhibitor, Keytruda. The company’s biggest revenue driver, Keytruda, alone accounted for more than 50% of the company’s pharmaceutical sales d ...