Question What is cancer? Responses Cancer is when abnormal cells in the body keep growing and damage healthy parts of the body. Cancer is when abnormal cells in the body keep growing and damage healthy parts of the body., Cancer is a disease in which the joints swell and become painful. Cancer is a disease in which the joints swell and become painful. Cancer is when the body makes extra mucus, so it is harder to breathe. Cancer is when the body makes extra mucus, so it is harder to breathe. Cancer is when the body is always sick and cannot heal