A tumor is a mass of abnormal cells that grow uncontrollably in the body. Tumors can be benign, meaning they are not cancerous and usually do not spread, or malignant, which means they are cancerous and can invade nearby tissues or spread to other parts of the body. Common types of tumors include those found in the breast, lungs, and brain. The exact cause of tumors can vary, but factors like genetics, exposure to certain chemicals, and lifestyle choices can play a role. Early detection through screenings, such as mammograms for breast tumors, is crucial for effective treatment and better outcomes.