Also note that most pre-cancerous and even post-cancerous cells are dealt with easily by the immune system. Its a very small minority of cancer cells that escape, you would end up just driving yourself crazy by sensing/noticing each one. This is why they aren't recommending mammograms, pap smears, or prostate exams as much or for as wide an age range as they used to, for young and healthy immune systems, treatment has worse outcomes than just letting the body do its thing.