Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. 1- masturbation has both positives and negative effects positive effect is that it will remove the sperms from the body and make room for newer sperms as the process of sperm formation is ever going in men, it is bad in a sense that excessive masturbation does leads to loss of libido and lesser stimulation by natural intercourse 2-in routine masturbation does not causes prostate problem but keep in mind that during ejaculation the prostate also squeezes to release its fluid which contributes in semen so transient urinary obstruction due to prostatic contraction or pain in elvis may occur 3-no masturbation does not cause shrinkage of testes 4-yes there are studies that proves the relation of excessive masturbation with prostatic cancer as excessive masturbation will cause more testosterone to release and this will have effect on prostate which could cause prostatic cancer the proof of this is that the castrated males who were castrated in there early teens never develop prostatic cancer. Hope I have answered your query. Let me know if I can assist you further.