What is a tumor?

• A. A normal tissue growth
• B. A mass of abnormal cells
• C. A virus
• D. A bacterial infection

Answer: (B)

A tumor is a lump that forms when cells start multiplying in an abnormal, uncontrolled way. That’s why it’s described as a mass of abnormal cells—the growth isn’t normal tissue growth, but cells that have lost the usual controls on division. Normal tissue growth is kept in check by signals that tell cells when to divide and when to stop; when those controls fail, a tumor can develop. Tumors can be benign, staying in one place, or malignant, invading nearby tissues and potentially spreading as cancer. Infections caused by a virus or bacteria involve different processes and aren’t defined by a lump of abnormal cells, though some infections can contribute to cancer risk later. So the best description is a mass of abnormal cells.