It is my understanding that excess testosterone can take prostate cancer from „it grows so slowly you’ll die of something else first“ to something that kills you quickly.
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.
Of course there are many types of cancer so this may not be true for all prostate cancers.