Abstract: PD61-09
Sources of Funding: This research was supported by the Intramural Research Program of the National Cancer Institute, NIH

Introduction

Tumor volume measured on radical prostatectomy (RP) specimen has been shown to be associated with adverse pathologic and oncologic outcomes; however, it is difficult to calculate and cannot contribute to preoperative decision making. Advances in imaging technology may facilitate the prediction of prostate cancer outcomes prior to surgery. In this study, we evaluated the predictive value of the index tumor volume (ITV) calculated from prostate MRI in analyzing adverse pathologic outcomes following RP in a higher risk cohort.

Methods

Clinical and pathologic data from a prospectively maintained, single-institution database were analyzed for patients who underwent 3T MRI prior to RP (without prior therapy) between 2007 and 2016, with an index tumor defined as a T2-visible lesion with the longest diameter. ITV was calculated from T2W MRI by multiplying length by width by depth by 0.52 to generate the volume of an ellipse. Adverse pathologic outcomes were determined on whole mount RP specimens, and defined as positive margins (PM), extracapsular extension (ECE), positive lymph nodes (LNI), and seminal vesicle invasion (SVI). Logistic regression was used to assess associations of clinical, imaging, and histopathological variables with adverse pathologic features. Receiver operating characteristic curves were used to characterize and compare ITV performance with Partin tables.

Results

In our study period, 464 patients met our inclusion criteria. In our cohort, median age and PSA were 60 years (IQR 10) and 6.21 ng/ml (IQR 6), and 24.4% were &[Prime]high risk&[Prime] (Gleason 8-10) on biopsy . 15.6% of patients had PM, 23.5% ECE, 6.3% LNI, and 6.5% SVI. Patients with adverse outcomes were found to have larger median ITV (PM: 1.236cc vs 0.832cc, p=0.045; ECE: 1.388cc vs 0.771cc, p<0.001; LNI: 2.750cc vs 0.801cc, p<0.001; SVI: 2.269cc vs 0.806cc, p<0.001). On multivariate analysis, ITV was found to be an independent predictor of ECE (OR: 1.211, p=0.005), LNI (OR: 1.366, p<0.001), and SVI (OR: 1.305, p=0.002), but not PM (OR: 1.052, p=0.300). ITV alone and ITV+PSA were found to have predictive ability comparable to that of Partin tables (ECE: ITV_AUC: 0.660 vs. ITV+PSA_AUC:0.721 vs. Partin_AUC: 0.717, LNI: ITV_AUC: 0.802 vs. ITV+PSA_AUC:0.881 vs. Partin_AUC: 0.873, SVI: ITV_AUC: 0.749 vs. ITV+PSA_AUC:0.762 vs. Partin_AUC: 0.806).

Conclusions

We demonstrate that Index Tumor Volume measured on T2W MRI is an independent predictor of ECE, LNI, and SVI following RP. We believe this easily calculated preoperative marker provides additional prognostic information, particularly in higher risk cohorts.

Funding

This research was supported by the Intramural Research Program of the National Cancer Institute, NIH