Actually, the whole concept of cancer screening is questionable. For example, you often hear the idea that catching cancer early extends your life span. However, the reality is that cancer has a time line of something like 20 years between the time you get it and the time it kills. If you catch the cancer at year 15, you will have five years to live, even without treatment. If you catch it at year 5, you have 15 years to live even without treatment. This biases the treatment statistics and makes it appear that catching it at year 5 gave the patient 10 extra years of life. This makes everyone think catching early is always best, but unless you take into account the natural life time of the disease, really don't know if treatment helps. Now if catching it early gave you 30 more years of life on 20 year disease, that would be real evidence of successful treament.