What is the primary characteristic of cancer?

Cancer is a group of diseases characterised by the abnormal and uncontrolled growth of cells. In a healthy body, cells grow, divide, and die in an orderly, regulated manner controlled by genes such as tumour suppressors and proto-oncogenes. When these regulatory mechanisms fail due to genetic mutations, cells begin to multiply without restraint, forming masses of tissue called tumours.

Not all tumours are cancerous. Benign tumours do not spread to other parts of the body. Malignant tumours, however, can invade surrounding tissues and spread to distant organs through the blood or lymphatic system in a process called metastasis. It is this uncontrolled proliferation and potential to metastasise that defines cancer.

The other options describe characteristics of different medical conditions. Sudden seizures and loss of consciousness are associated with epilepsy or other neurological disorders. Chronic inflammation in the lungs is a hallmark of conditions such as chronic obstructive pulmonary disease (COPD) or asthma. Increased blood sugar levels are the defining feature of diabetes mellitus. While cancer may sometimes co-occur with these conditions, none of them describes cancer's primary characteristic.