What my doctor has told me, after attending a urology + prostate cancer conference, is to think of the prostate as a sponge that absorbs testosterone. And once the sponge overflows, prostate cancer can be triggered.

But once cancer has occurred, adding more testosterone doesn't matter because the sponge is already super-saturated.

In fact, doctors who have this perspective will permit men with prostate cancer to continue testosterone therapy.

My father was recently diagnosed with prostate cancer and the first treatment was eradicating all testosterone from his body as the affected cells were "feeding" from it. It's not a cure as they tend to find other ways to grow with time but testosterone does make it faster.

Of course there are many types of cancer so this may not be true for all prostate cancers.