Which of the following is a characteristic of malignant cells?

• A. Enhanced function of tumor suppressor genes
• B. Mutated proto-oncogenes
• C. The ability to undergo apoptosis
• D. Controlled cell growth

Answer: (B)

Mutations in growth-promoting genes turn normal regulators into drivers of cancer. Proto-oncogenes normally respond to signals to push cells through the cycle, but when they mutate, they become oncogenes that push cells to divide continuously, even without proper cues. That unregulated proliferation is a hallmark of malignant cells.

In contrast, enhanced function of tumor suppressor genes would slow or stop growth, which is not what malignant cells do. The ability to undergo apoptosis is a defense mechanism that malignant cells often evade; they resist death rather than readily die. And while normal cells show controlled growth, malignant cells exhibit uncontrolled, unregulated growth. Thus, mutating proto-oncogenes best accounts for malignant behavior.