Final answer:
Cancer is a group of over 100 different diseases characterized by uncontrollable cell growth that can spread throughout the body, forming tumors and disrupting bodily functions.
Step-by-step explanation:
Cancer is a large group of heterogeneous diseases characterized by abnormal cell growth with the potential to invade or spread to other parts of the body. This uncontrolled cell division can result in a mass of abnormal cells known as a tumor, which may be benign if it doesn't harm surrounding tissues, or malignant if it invades other tissues.
Factors contributing to cancer can be genetic, environmental, or a combination of both. Although cancer forms gradually, it becomes a significant health issue when these cancerous cells disrupt the normal functions of the body.