Merck is developing several cancer drugs, including Keytruda, which blocks the PD-1 receptor and unleashes the immune system to attack cancerous tissue, approved for more than 40 types of tumors such as melanoma, non-small cell lung cancer, and kidney cancer.[3] Merck and AstraZeneca's Lynparza has received approval in Japan for the maintenance treatment of ovarian, prostate and pancreatic cancer after chemotherapy.[2] These companies are among the five and ten largest pharmaceutical companies by revenue.[2] Merck is also testing $1 billion Lenvima for thyroid, liver, and kidney cancer, $0.5 billion WELIREG for VHL-associated tumors, and $0.4 billion WINREVAIR for pulmonary arterial hypertension.[3] The firm canceled a phase III trial of Xevinapant for head and neck cancer after an independent panel concluded it was unlikely to meet the goal of prolonging progression-free survival; she paid 188 million euros for it in advance.[4] Merck is investigating targets such as DNA damage (DDR, including ATM and ATR), CEACAM5, MET amplification, PD-L1 and TIGIT in immuno-oncology.[6] Merck and Moderna's skin cancer vaccine maintained remission in more patients in trials.[8]