What defines cancer in terms of cell behavior?

Cancer is characterized by abnormal and uncontrolled cell division. This means that the cells do not respond appropriately to the regulatory mechanisms in the body that normally control the cell cycle. In healthy tissues, cell division is a tightly regulated process where cells divide to replace old or damaged cells and to maintain normal function. However, cancer cells circumvent these controls, leading to excessive proliferation.

Cancer can arise from various factors, including mutations in genes that regulate the cell cycle, leading to an inability to stop dividing when they should. This uncontrolled growth can result in tumors, which can invade nearby tissues and spread to other parts of the body through a process known as metastasis. Understanding this behavior is crucial in oncology to develop effective treatments and interventions.

The other choices do not accurately represent the nature of cancer cell behavior. Controlled cell division describes normal cellular processes, while the options regarding dividing only once or in response to nutrients do not pertain to cancerous cells, which can continue to proliferate despite unfavorable conditions.