Dr. Peter McKenna:

I could hazard offering an answer on that. Once a woman has a visible, invasive cervical cancer, she will probably live without treatment for about 18 to 24 months. However, we know, and this is one of the best studied areas of screening in any part of the body, that to get to that stage there is a pre-invasive stage that may take as long as 12 or 15 years, which starts off as a mild abnormality and usually progresses at a reasonable rate to a severe abnormality and then to cancer. At any of those stages it can revert back to being normal, but the nearer one gets to having an invasive cervical cancer, the more likely it is to progress into being an invasive cancer. The premise of the Chairman's question is whether one has several opportunities to catch it before it becomes invasive. The answer is one has many opportunities. This test, which has a high false negative rate, works because one has several attempts at it over the ten or 12-year period before it turns into an invasive cancer. If it progressed more rapidly and the test was as good as it is now, it would not work but because it progresses so slowly, this test, which has error built into it, works.