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 1 or more risk factors does not mean that you will develop cancer. Many people have at least 1 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. 

Since the primary cancer is not known for this cancer type, it is very difficult to outline risk factors for it. However, there are some common risk factors for many cancer types, which may apply to an increased risk of getting cancer of unknown primary:^[2] 

• smoking – more than half of the patients diagnosed with cancer of unknown primary have smoked at some time in their life 
• older age 
• poor diet – for example, not enough fruits and vegetables 
• too much alcohol 
• obesity 
• exposure to large amounts of radiation 
• family history – if your family has a history of certain cancers, then your risk of cancer can increase