What is a defining characteristic of cancer?

A defining characteristic of cancer is that cells divide uncontrollably. This uncontrolled division is a fundamental aspect of cancerous cells, which disregards the normal regulatory mechanisms that govern cell growth and replication. In healthy tissues, cell division is a tightly controlled process, with checks and balances in place to ensure that cells only divide when necessary and to the correct extent.

In cancer, however, mutations in the DNA of cells can lead to the loss of these regulatory controls. For example, certain genes known as oncogenes can become activated inappropriately, promoting excessive division, while tumor suppressor genes, which normally inhibit cell division, may be inactivated. This results in the formation of tumors and the potential spread of cancer cells to other parts of the body.

The other choices do not accurately describe cancer's characteristics. Rapid self-repair of cells does not define cancer—rather, cancerous cells often accumulate damage over time without repairing themselves properly. Cells that remain inert do not exhibit the active divisions characteristic of cancer. Lastly, while cells that do not undergo apoptosis (programmed cell death) can contribute to cancer development, the defining feature is more accurately the uncontrolled division of those cells. Apoptosis in healthy cells serves a protective function against cancer,