Temsirolimus is a medication used primarily in the treatment of advanced renal cell carcinoma, a type of kidney cancer. It belongs to a class of drugs known as mTOR inhibitors, which work by blocking a specific protein that helps cancer cells grow and divide. By inhibiting this protein, temsirolimus can slow down the progression of the disease. This drug is typically administered through an intravenous infusion and is often used in patients who have not received prior treatment for their cancer. Common side effects may include fatigue, nausea, and increased risk of infections, making it important for patients to be monitored closely during therapy.