What is Index Lesion in prostate cancer? What is the significance of biopsy of Index Lesion? Index lesion and clinical significance of prostate cancer. Dr. Anton Titov, MD. What is Index Lesion in prostate cancer? What is the significance of biopsy of Index Lesion? How to select the appropriate treatment in prostate cancer? Dr. Mark Emberton, MD. Index Lesion is an interesting concept in prostate cancer. We've talked about active surveillance in prostate cancer. In active surveillance we make a judgment that the patient has prostate cancer that is below a certain threshold. His cancer will not progress, or is not risky, or is not clinically significant. And above that threshold prostate cancer is likely to progress. So we draw a line and we say. "You, Sir, need treatment”. And we say to another patient, "You, Sir, do not need treatment". And the Index Lesion is exactly the same in prostate cancer. We are making the same judgment about the risk of prostate cancer. But instead of doing it at the patient level, we're doing it at the prostate level. Dr. Mark Emberton, MD. Index Lesion is something that we can see, and biopsy, and risk stratify. That process gives us a prostate cancer that we think is clinically significant. A prostate cancer of significant risk. It is compared with a prostate cancer lesion that we can't see and can't biopsy. That lesion we determined to be of low-risk.