JsHill,
Welcome to the forum. Sorry you need to be here but glad you found us.
When someone asks a question and I don't have a clue I will often repair to Google-land to see if I can find anything useful and then I return to the question and pretend I knew what they were talking about
all along. Sometimes I find myself out of my depth in the information I find.
To save the time of the other guys here on the forum who like to pretend to be smarter than they are, hemizygous and homozygous deletion are two different ways the PTEN gene can be dropped out of a strand of DNA by the mutations that occur in prostate cancer cells. The homozygous form seems to be present at the same level of occurrence in most prostate cancer regardless of aggressiveness but the hemizygous form of deletion occurrs more frequently in higher-gleason, more-aggressive cancers. Thus, finding hemizygous deletion in the tiny little blob of tissue removed at biopsy may be a marker for higher risk of aggressiveness, or so the rather-new theory goes.
Here are a couple of links:
ptendeletion.net/www.ncbi.nlm.nih.gov/pubmed/20590547 (Good luck reading this one...)