The vast majority of cancers, some 90–95% of cases, are due to genetic mutations from environmental and lifestyle factors.
The remaining 5–10% are due to inherited genetics. Environmental, as used by cancer researchers, means any cause that is not inherited genetically, such as lifestyle, economic, and behavioural factors and not merely pollution.
Common environmental factors that contribute to cancer death include tobacco (25–30%), diet and obesity (30–35%), infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), stress, lack of physical activity and pollution.
It is not generally possible to prove what caused particular cancer because the various causes do not have specific fingerprints.
For example, if a person who uses tobacco heavily develops lung cancer, then it was probably caused by the tobacco use, but since everyone has a small chance of developing lung cancer as a result of air pollution or radiation, the tumour may have grown for one of those reasons.
Excepting the rare transmissions that occur with pregnancies and occasional organ donors, cancer is generally not a transmissible disease.