Tumor cells are abnormal cells that grow and divide uncontrollably, forming masses known as tumors. Unlike normal cells, which follow a regulated life cycle, tumor cells can evade the body's mechanisms that typically prevent excessive growth. They can be benign (non-cancerous) or malignant (cancerous), with malignant tumors having the potential to invade nearby tissues and spread to other parts of the body. These cells often exhibit changes in their genetic material, which can lead to altered behavior and characteristics. Tumor cells can also develop resistance to treatments, making them challenging to eliminate. Understanding cancer and the behavior of tumor cells is crucial for developing effective therapies.