Tumor formation refers to the process by which a group of abnormal cells, or a tumor, grows and develops within an organism. This can occur when normal cell division is disrupted, leading to uncontrolled growth that forms a mass of tissue. Tumors can be benign (non-cancerous) or malignant (cancerous), with the potential to invade surrounding tissues and spread throughout the body if left untreated. The term "tumor formation" is often used interchangeably with "tumor growth," although tumor growth refers specifically to the increase in size of an existing tumor over time, while tumor formation encompasses both the initial development and subsequent growth of a tumor.