A risk factor is any factor that is associated with increasing someone’s chances of developing a certain condition, such as cancer. Some risk factors are modifiable, such as lifestyle or environmental risk factors. Others cannot be modified, such as inherited factors or whether someone in the family has had cancer. 

Having one or more risk factors does not mean that you will develop cancer. Many people have at least one risk factor but will never develop cancer, while others with cancer may have had no known risk factors. Even if a person with cancer has a risk factor, it is usually hard to know how much that risk factor contributed to the development of their disease. 

Leukaemia risk factors 

There are different risk factors associated with developing different types of leukaemia. 

Acute lymphoblastic leukaemia (ALL) risk factors include: 

• exposure to high levels of radiation 
• exposure to certain chemicals, including the solvent benzene, and chemotherapy medicines 
• infection with Epstein–Barr virus or human T-cell lymphoma/leukaemia virus 1 (HTLV-1) 
• certain genetic syndromes, including Down syndrome, Klinefelter syndrome, Fanconi anaemia, Bloom syndrome, ataxia-telangiectasia, neurofibromatosis and Li-Fraumeni syndrome 
• being male – ALL is more common in males than in females 
• age – ALL is more likely to occur in children and in adults over 50 years old ^[6] 
• having an identical twin with ALL. 

Acute myeloid leukaemia (AML) risk factors include: 

• smoking 
• obesity ^[7]
• exposure to high levels of radiation 
• exposure to certain chemicals, including the solvent benzene, and chemotherapy medicines 
• certain blood disorders, including myelodysplasia ^[8] and chronic myeloproliferative disorders 
• certain genetic syndromes, including Down syndrome, trisomy 8, Fanconi anaemia, Bloom syndrome, ataxia-telangiectasia, Diamond–Blackfan anaemia, Shwachman–Diamond syndrome, Li–Fraumeni syndrome, neurofibromatosis type 1 and severe congenital neutropaenia 
• having an identical twin or another close relative with AML 
• age – the risk of AML increases with age 
• being male  – AML is more common in males than in females 
• having had treatment for ALL in childhood. 

Chronic lymphoblastic leukaemia (CLL) risk factors include: 

• exposure to certain chemicals, possibly including the herbicide Agent Orange, and some pesticides 
• having certain genetic abnormalities ^[9]
• having a close relative with CLL 
• age – CLL is more common in people over 50 years old 
• being male – CLL is slightly more common in males than in females 
• racial background – CLL is more common in Russian or eastern European Jews (Ashkenazi Jewish background). and less common in people with an Asian background. 

Chronic myeloid leukaemia (CML) risk factors include: 

• having a genetic abnormality known as the Philadelphia chromosome or BCRABL gene (this abnormality is not inherited – it develops during life) ^[10]
• exposure to high levels of radiation 
• age – the risk of CML increases with age 
• being male – CML is slightly more common in males than in females 
• exposure to the solvent benzene. ^[11]