When a cell divides by mitosis, it is usually controlled by cell cycle checkpoints. If a cell has abnormalities it can start uncontrollably dividing, producing a mass of abnormal cells called a tumour. Tumours can be benign (doesn’t spread), or malignant. Malignant tumours are cancerous and can grow into surrounding tissue, including organs, affecting the usual function of the body. These cancerous cells can break away from the tumour and travel through the blood or lymphatic system to other parts of the body, creating secondary tumours called metastases. There are over 200 types of cancer, but the most common are breast, lung, prostate and bowel cancer.
The biggest, and most preventable, cause of cancer is smoking. It is responsible for about 75–80% of lung cancers- the most common type of cancer, with one of the lowest survival rates. Cancer causing chemicals are known as carcinogens. Cigarettes contain more than 70 carcinogens, for example, benzene, polonium-210, benzo(a)pyrene and nitrosamines. Once they enter the body, cytochrome P-450 enzymes catalyse the process of metabolic activation, which enables them to bind covalently to DNA, forming DNA adducts. A build-up of DNA adducts causes insertion mutations because it stops DNA polymerase processing the DNA correctly during DNA replication. This leads to a frameshift mutation which can ultimately result in cellular proliferation and cancer.
Alison C. MacKinnon, Jens Kopatz, Tariq Sethi (2010) The molecular and cellular biology of lung cancer: identifying novel therapeutic strategies, British Medical Bulletin, 95(1), 47-61
(2010) How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. NCBI
Stephen S. Hecht (1999) Tobacco smoke carcinogens and lung cancer. Journal of the national cancer institute, 91(14), 1194-1210
How smoking causes cancer. Cancer research