Which of the following best defines a tumor?

• A. A benign tissue growth
• B. A mass of abnormal cells
• C. A normal tissue
• D. An infectious disease

Answer: (B)

A tumor is a lump formed by cells that have started to grow in an abnormal way, creating a mass. This definition fits both benign tumors (non-cancerous) and malignant tumors (cancerous), since it’s about the presence of a mass of abnormal cells, not about whether it’s harmful or invasive. It’s not normal tissue, and it’s not an infectious disease, which involves pathogens. Saying it’s only a benign tissue growth misses the important idea that tumors can be either benign or malignant, so describing a tumor as a mass of abnormal cells is the most accurate and inclusive definition.