Ok if they can "take years to show symptoms and become a problem" aren't they in fact developing during this time? And there are extremely slow growing cancerous tumors. I think with most cancers you aren't fine on Monday and have a cancerous tumor by Friday. Fox example, don't some types of breast cancers start miniscule and slowly grow? It may take a while for it to grow big enough for detection but it's still cancerous as it grows.