Actually, I think it's because some parasites cause affects that are symptoms of cancer, not actual cancer.
Cancer is formed from rogue cells with bad genetic coding that have split one too many times, causing them to grow out of control due to some mechanisms within the cell. This causes this specific part of the body that is cancerous to dreg resources from the rest of the body to support its out of control growth. In order to do this, blood vessels actually grow from the blood vessels near the cancer and become rooted in the cancer (another lesson).
It would make sense to have a cancer test in this case. Hell everybody has cancer after they're 60. You will have some sort of cancerous polyp in your colon by then. Humans simply aren't meant to live that long.
Yes, I was, uh... I was thinking about ordering the tape, the videotape... about the college girls and the... the wild... the wildness. They're going wild or something? Somebody told me... about going wild.