In contrast to benign tumours, which do not spread, cancer is a group of diseases characterized by abnormal cell growth and the potential to invade or spread to other parts of the body. A lump, abnormal bleeding, a persistent cough, unexplained weight loss, and a change in bowel movements are all possible signs and symptoms. These symptoms may indicate cancer, but they may also be caused by other conditions. Humans are impacted by over 100 types of cancer.

About 22% of cancer deaths are caused by smoking. Obesity, poor diet, inactivity, or excessive alcohol consumption account for another 10%. Certain infections, exposure to ionizing radiation, and pollutants in the environment are additional factors. Infections like Helicobacter pylori, hepatitis B, hepatitis C, the human papillomavirus, the Epstein-Barr virus, and the human immunodeficiency virus (HIV) account for 15% of cancer cases in developing countries. A cell's genes are altered, at least partially, by these factors. Before cancer develops, numerous genetic changes are typically required. Genetic defects are the cause of between 5 and 10% of cancers. Certain signs and symptoms or screening tests can help find cancer. Following that, medical imaging and a biopsy are typically used to confirm the diagnosis.