Which of the following best describes a benign tumor?

A benign tumor is characterized as an overgrowth of normal cells that cannot invade other tissues. This definition highlights the key features that distinguish benign tumors from malignant tumors. Unlike malignant tumors, which consist of abnormal cells with the ability to spread to other areas of the body (a process known as metastasis), benign tumors remain localized. As a result, they typically do not pose the same level of threat as malignant tumors.

Moreover, the cells in benign tumors maintain their normal structure and function, which is why they do not invade surrounding tissues or organs. They may still grow larger and exert pressure on nearby structures, but they do not spread throughout the body. This benign behavior is a critical aspect to understand when discussing tumor biology.

The other options describe qualities or characteristics that do not align with the definition of a benign tumor. For instance, malignant tumors are specifically the overgrowth of abnormal cells that have the capacity to invade other tissues and are often cancerous. Additionally, the notion of a collection of dead cells forming a mass does not accurately define any type of tumor, as tumors consist of living cells. Understanding these distinctions is essential in the study of cancer biology and tumor classification.