There is no specific preventive measure for prostate cancer. Some people have a higher risk like those: 
– Having two close relatives (eg father, grandfather, uncle) who have been diagnosed with prostate cancer;
– Having a close relative diagnosed with prostate cancer before the age of 45;
Of African or Caribbean origin.
Food an prostate cancer : is there a correlation ?
Food could also play a role. Several epidemiological studies conducted in the 1990s [2; 3; 4] have highlighted the bad influence of a diet containing too much fat. Animal fats would be the most harmful.
Men who do not eat fish would have two to three times more risk of prostate cancer. 
Finally, consumption of flaxseed could slow the prostate cancer spread by decreasing the level of testosterone in the blood (testosterone is an hormone that causes progression of prostate cancer). 
 Data source : « Le Cancer de la Prostate » La Ligue contre le cancer – Septembre 2009
 J Natl Cancer Inst 1993;85:1571-9
 Lipids 1992;27:798-803
 J Natl Cancer Inst 1993;85:1538-40
 – Lancet 2001 Jun 2 ;357(9270) :1764-6
 – Urology 2001 Jul ;58 (1) :47-52