Most testicular cancers are discovered by the men who have them, either by accident or by a regular self-examination.

As with most cancers, the key to successful treatment is early detection. And the key to early detection is careful testicular self-examination.

The National Cancer Institute recommends that men examine their testicles once a month, during or soon after a warm shower or bath, when the wall of the scrotum is relaxed and abnormalities are easy to feel.

"While standing," NCI suggests, "the man gently rolls one testicle between his thumb and fingers, checking for lumps, swelling or other changes. The process is repeated with the other testicle.

"The normal testicle feels smooth, egg-shaped and rather firm."

The most common warning sign of cancer of the testis, NCI says, is "a small, hard lump, about the size of a pea." But any abnormality -- particularly scrotal swelling, pain, unusual tenderness or a feeling of heaviness -- should be reported to a doctor immediately. These symptoms do not necessarily mean cancer, but a doctor can make the diagnosis.

Some difference in size or shape between the two testicles is normal, said Dr. Frances DuRocher, an internist with Group Health Association.

"What you're looking for is abnormal swelling and lumps."