Prostate cancer is one of the most common forms of cancer in older men. The prostate is a gland that lies just underneath the bladder. Prostate cancer and benign prostatic hyperplasia swell the prostate, often causing problems with the urethra. No medical evidence suggests that use of a bicycle seat causes prostate problems, and exercise may protect against cancer in general, to some degree. Keeping comfortable on a bicycle seat, however, is advisable; pain from cycling suggests a posture or muscle problem.
Choose a saddle that reflects your riding position. If you have had prostate surgery or are riding again after many years, you will not be riding aggressively and will need a seat that forces you to sit high up.
Adjust your saddle to fit your riding style. Often the bike shop from which you bought the saddle from will help you do this, though it is easy to do yourself either using an Allen wrench or a clip lock mechanism on your saddle, depending on the design.
Change your riding style. Sit higher on the seat and avoid leaning forward. Minimise the weight on your hands and shift it to the seat. Cycle slower for further distances if you are intent on keeping fit.
Stop if you are feeling extreme discomfort. Pain happens for a reason and should not be ignored. Mild discomfort from a saddle is to be expected, especially when it is new, but if the pain continues after you dismount, avoid cycling until you can ride without extreme pain.
Consult a doctor if you are seriously concerned. During recovery from surgery, cycling can be a good way of regaining fitness, but if it causes you serious pain, you may have to change your exercise regimen.