Keytruda (pembrolizumab) is a prominent immunotherapy drug that serves as a cornerstone in modern cancer treatment, approved for over 22 types of cancer including lung, melanoma, and colorectal cancers. As a PD-1 inhibitor, it enhances the immune system's ability to recognize and attack cancer cells by blocking the PD-1 pathway, which cancer cells use to evade immune detection. Keytruda is typically administered through intravenous infusion every 3 to 6 weeks, with a newer version allowing for faster subcutaneous injections. The cost of Keytruda is significant, often exceeding $12,000 per dose, while in India, it ranges from ₹1.5 lakh to ₹2.16 lakh per vial. The drug's success rate varies widely depending on the type and stage of cancer, with some patients, particularly those with advanced melanoma, experiencing a 31% reduction in the risk of death compared to older treatments. While Keytruda can significantly improve survival rates and shrink tumors, it is not a guaranteed cure and is often used in conjunction with other therapies.