Cancer and DNA, conceptual composite image. Scanning electron microscopy (SEM) and computer generated image (CGI) of DNA (deoxyribonucleic acid) molecules (helices) and dividing cancer cells. Cancer is a genetic disease, it arises from changes to genes that control how cells function, especially how they grow and divide. Genetic changes that promote cancer can be inherited if the changes are present in the germ cells (eggs and sperm). Cancer-causing genetic changes can also be acquired, as the result of errors that occur as cells divide or from exposure to carcinogenic substances that damage DNA, such as certain chemicals in tobacco smoke, or ultraviolet radiation from the sun. Genetic changes that occur after conception are called somatic (or acquired) changes.