A risk factor  is anything that increases a person’s chance of developing cancer. Although risk factors often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.
In general, leukemia can be caused by a genetic mutation (change) that is inherited (passed from generation to generation within a family) or environmental factors, such as smoking, or chemical or radiation exposure. However, most often the cause of leukemia is not known.
The following factors may raise a person’s risk of developing PLL or HCL:
Age. HCL occurs most often in people between ages 40 and 70.
Gender. Men are five times more likely to develop HCL than women.
Race/Ethnicity. HCL is more common in white people and Ashkenazi Jewish men. PLL and HCL are rare in people of Japanese or Southeast Asian descent.