I have to admit I hadn't heard of it before. 4-MU (4-Methylumbelliferone) has just joined the list of documented prostate cancer miracle cures if you are a mouse. A study released last month found that it seemed to prevent progression of prostate cancer in human-xenograft mice, and particularly exciting, it totally prevented the development of bone metastases.
See:
www.ncbi.nlm.nih.gov/pubmed/25868577There doesn't seem to be any actual human research yet for its use in prostate cancer. But there is a fair amount of clinical trial information available from Europe where it is approved to treat liver complaints and trials have shown it to be quite safe at the usual doses.
A brief scan of my usual snake oil vendors has failed to turn up a source so it may be expensive and hard-to-find, especially with the buzz it has had lately.