TABLE 1.

Extrinsic factors contributing to tumorigenesis.

Risk factor	Type	Cancer	References
UV and other ionizing radiation	Mutagen	skin cancer, leukemia, lung cancer	Bizzozero Jr et al. (1966), Veierød et al. (2003), Turner et al. (2011)
Cigarette smoke	Mutagen	Lung cancer	(Chapman et al., 2016); Guida et al. (2015)
Human papilloma virus	Mutagen	Head and neck cancer, Cancers of urogenital tract	(Cai et al., 2018, Sabatini and Chiocca 2020)
Hepatitis B virus	Mutagen	Liver Cancer	MacLachlan et al. (2015)
Asbestos	Mutagen	Pleural Mesothelioma	Tossavainen (2004)
Alcohol	Dietary factor	Breast cancer, liver cancer	Cancer (2002), Schütze et al. (2011)
Red Meat	Dietary factor	Breast cancer	Lo et al. (2020)