Give me 3-5 sentences on how cancer can start

Cancer can start when cells in the body begin to grow uncontrollably and form a mass of tissue known as a tumor. This uncontrolled growth can be caused by genetic mutations, environmental factors such as exposure to carcinogens, or a weakened immune system. Cancer can also develop from the spread of abnormal cells from one part of the body to another, known as metastasis. Early detection and treatment are critical in managing and potentially curing cancer.