Even if your cancer was treated with initial primary therapy (surgery or radiation) there is always the probability that the cancer will reoccur.
About 20-30% of men will relapse (have the cancer detected on a blood test) after the five-year mark following initial therapy. The likelihood of recurrence depends on the extent and aggressiveness of the cancer.
Several online tools have been assembled to help predict the likelihood of recurrence. Try inputting your own information into this prediction tool. http://urology.jhu.edu/prostate/hanTables.php
The Role of PSA
Prostate cancer recurrence is determined by a rising PSA following treatment. After surgery, PSA levels should drop to zero. When PSA levels rise above 0.2 ng/mL, the cancer is considered to be recurrent. After treatment with radiation, PSA levels will never drop completely to zero. However, the PSA should level out at a low number, called the nadir. When PSA levels rise 2 points from its lowest value the cancer is considered to be recurrent.
Clinicians use the change in PSA over time as a marker for the aggressiveness of the recurrence. After a certain amount of time, the cancer will be visible radiographically (i.e. via CAT scans or bone scans). Prostate cancer can recur locally in the pelvis or elsewhere in the body. The location of the recurrence is determined by these radiographic studies.