The causes of cancer are varied and can be external or internal to the body.
External causes are related to the environment and the habits or customs of a social and cultural environment. Internal causes are, in most cases, genetically predetermined and are linked to the organism’s ability to defend itself against external aggressions. These causal factors can interact in various ways, increasing the likelihood of malignant transformations in normal cells.
Of all cases, 80% to 90% of cancers are associated with environmental factors. Some of them are well known: cigarette smoking can cause lung cancer, excessive exposure to the sun can cause skin cancer, and some viruses can cause leukemia. Others are under study, such as some components of the foods we eat, and many are still completely unknown.
Aging brings changes to cells that increase their susceptibility to malignant transformation. This, added to the fact that the cells of elderly people have been exposed for longer to different risk factors for cancer, partly explains why cancer is more frequent in these individuals.