This study was to prove results and monitor side effects.
Propecia is been used since 1990 and until now it is considered to be very safe and i haven't heard of any patient that had cancer.
Also, I have not seen anyone who stayed on Propecia go bald, but I have seen many, many men who were taking it and decided to stop, who then went either very bald or very thin.
You might find this page useful:
http://en.wikipedia.org/wiki/Finasteride