Prostate Cancer is a leading cause of cancer death among men. Current treatment involves surgical removal of the cancer followed by chemical depletion of androgen (testosterone) which prevents growth and expansion of any residual prostate cancer cells. However, prostate cancer cells which have lost their dependence on exogenous androgen inevitably grow out and reestablish the tumour. We have found that a large proportion of prostate cancers are associated with abnormally elevated levels of a growth stimulatory protein called semaphorin3C (Sema3C), which supports the growth of prostate cancer. We propose to interfere with the function of Sema3C to inhibit prostate cancer cell growth.