ehwest, continuing with the example you give about prostate cancer, one of the problems is first correctly identifying that indeed a man has prostate cancer. The PSA test currently being used for screening gives a lot of false positives and false negatives. If a man has elevated PSA test the doctor will recommend a biopsy which is done on the prostate area most likely to be cancerous, but the cancer may be in another area not being biopsed. So there you have it a very inefficient, possibly inaccurate, expensive and anxiety producing precess to determine if you have prostate cancer or not. A blood test similar to OvaDX for prostate cancer would tell you with a great degree of certainty if you have prostate cancer or not. Then the second step for treatment as you describe is to ascertain, using tools such as the Gleason scale, how aggressive the cancer is.
A similar situation occurs with ovarian cancer. There is no test now to accurately diagnose ovarian cancer. The CA-125 now being used is 50% accurate. So 50% of the women will go thorugh the unnecessary, anxiety producing process of extra testing and dangerous surgical procedures.
OvaDx in addition to screening will be also used for monitoring the cancer during treatment and remission.