A solid tumor is a type of cancer characterized by an abnormal mass of tissue that develops when cells proliferate uncontrollably. Unlike blood cancers, solid tumors occur in organs or tissues such as the breast, lung, prostate, or brain. They can be benign or malignant, with malignant tumors posing significant health risks. Solid tumors are a major focus of oncology research, diagnosis, and treatment, including surgery, radiation, chemotherapy, and targeted therapies.