What is the prevalence of prostate cancer in teens?

Uncommon. Never met a patient like this, although we don't usually check on them, either. However, i've never met someone who died of prostate cancer this young.
Very very rare. Primary cancer of the prostate is rarely ever diagnosed in anyone under the age of forty. While we do not screen these patients I have never read of a case of adenocarcinoma of the prostate in the teenage population.
Extremely rare. Prostate cancer that is caused by adenocarcinoma (the most common variant in adults) is not a disease of males in their teens but usually affects men over the age of 40. Only vary rare tumors that may arise from the prostate including rhabdomyosarcoma can be found teens.