Does the pituitary gland have anything to do with prostate cancer?

Not exactly: Prostate cancer is typically effected by testosterone. One way to treat prostate cancer is to reduce the testosterone levels to very low values. The main way that this is done today is by giving drugs that are gonadotropin releasing hormone agonists (gnrh). These drugs bind to the puitary to cause the release of FSH and LH which over time down regulate the production of testosterone.

indirectly: A strong positive association was observed between growth hormone efector igf-i levels and prostate cancer risk. Men in the highest quartile of igf-i levels had a relative risk of 4.3 (95 percent confidence interval 1.8 to 10.6) compared with men in the lowest quartile. This association was independent of baseline prostate-specific antigen levels.