Scientists do not know what causes the growth of malignant cells in the male reproductive system. There are several factors that increase a man’s risk of developing reproductive cancers. However, many men with reproductive cancers do not have any of the risk factors. These risk factors include:

• Family history. Having a brother or father who has prostate or testicular cancer raises a man’s risk of developing that type of cancer.
  
  
• Genetic mutations. Alterations in DNA that develop during a man’s life or are inherited from a parent. Gene mutations may account for 5 to 10 percent of prostate cancers, according to the National Cancer Institute, and appear to play a smaller role in testicular cancers.
  
  
• Age. As with most cancers, the risk of prostate and penile cancers increases with age. Testicular cancer usually affects young men.
  
  
• Race. Black Americans have a higher risk of prostate cancer than white Americans but lower risk of testicular cancer. Penile cancer is more common in Africa than in Europe and the United States.
  
  
• Diet. A diet high in animal fats and low in vegetables and fruits appears to increase the risk of prostate cancer and has been linked to increased risk of many other types of cancer.
  
  
• Smoking. Experts link smoking to increased risk of penile and many other types of cancer.
  
  
• Viral infections. Men with human immunodeficiency virus (HIV) and AIDS (acquired immune deficiency syndrome) appear to have a greater risk of testicular and penile cancers.  Infection with human papillomavirus (HPV) is a major factor in penile cancer.
  
  
• History of other cancers.
  
  
• Prostatic intraepithelial neoplasia (PIN). Changes in the structure of prostate gland cells. Many scientists think this is a risk factor for prostate cancer.
  
  
• Certain congenital conditions. Disorders that reduce male hormones, such as Klinefelter’s syndrome, increase the odds of developing testicular cancer.
  
  
• Skin disorders. A condition producing multiple moles has been associated with testicular cancer. Use of ultraviolet light and certain drugs has been associated with penile cancer.

The relationship of circumcision to risk for penile cancer is a matter of dispute. In some areas where there are high rates of penile cancer, circumcision is uncommon. However, experts belive that other factors, such as poor hygiene or viral exposure may be more closely associated with the cancer risk, not circumcision.