When addressing the concept of the index lesion, Dr. Briganti demonstrated several different definitions used in the literature as evidence to the fact that it is completely unclear what the index lesion really is. It is likely to assume that the index lesion is the largest volume lesion with the highest grade, which drives prostate cancer behavior and progression. Additionally, evidence was presented showing that in almost 30% of cases, even when one thinks the index lesion has been identified, other significant high grade lesions can coexist. Even when identifying a PIRADS 4 index lesion on multiparametric MRI, there is still a false positive value of 19-40% and false negative value of up to 70% of Gleason 7 (3+4) lesions.
Furthermore, genetic evidence was presented demonstrating heterogeneity of the same grade lesion in different patients and even in the same patient. This translates to the fact that Gleason 7 lesions could be completely different among patients and even in the same patient, obscuring the identification and even existence of one single index lesion.
Dr. Briganti concluded with a presentation of findings from his own work being presented in the EAU 2017 meeting. His study used multivariate regression analysis to ascertain the impact of the presence of non-index lesions on the risk of extra-capsular extension, seminal vesicle invasion, positive surgical margins, and lymph node invasion. Results showed that all factors were significantly affected by the presence of non-index lesions. This reinforces the notion that treating the index lesion is not as oncologically good as treating the entire gland.
Presented by: Dr. Alberto. Briganti, Milan (IT)
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto
at the #EAU17 -March 24-28, 2017- London, England