MP45-09 BODY MASS INDEX (BMI) AS PREDICTOR OF MORTALITY AFTER RADICAL PROSTATECTOMY: A COMPETING RISK ANALYSIS

Abstract

INTRODUCTION AND OBJECTIVES: It has been previously hypothesized that higher grade prostate tumors exhibit less predictable PSA secretion patterns as a consequence of cellular dedifferentiation. The purpose of this study is to investigate whether the relationship between PSA and biochemical recurrence (BCR) is different for high and low grade disease. METHODS: We identified 6,616 patients who underwent radical prostatectomy (RP) from 1992-2012 for clinically localized prostate cancer without neoadjuvant treatment. We first created Cox models to test for an interaction between PSA and clinical or pathologic high grade cancer (Gleason grade (GG) < 8 vs. GG 8-10). We then plotted five year risk of BCR as a function of PSA for patients with negative extracapsular extension (ECE), seminal vesical invasion (SVI), and lymph node invasion (LNI). RESULTS: 6,125 (93%) patients in the cohort had GG < 8, and 491 (7%) had GG 8-10 (Table 1). In total, 780 patients had a BCR and 165 had distant metastasis. We found a significant interaction between PSA and pathologic high grade cancer (p1⁄40.001), meaning the risk of BCR increases at different rates for low and high grade tumors as PSA increases. The figure shows the 5-year risk of BCR for low grade (GG < 8) and high grade (GG 8) patients by PSA level. We can see that the risk of BCR increases at only slightly different rates. For example, an increase in PSA from 10 ng/ml to 20 ng/ml increases recurrence risk from 8% to 11% (38% relative increase) and 48% to 52% (8% relative increase) for low and high grade cancers, respectively. There was no significant interaction between PSA and clinical high grade tumors (p1⁄40.2). CONCLUSIONS: There appears to be a small difference in relationship between preoperative PSA and BCR in high grade tumors when compared to lower grade tumors. While this difference is statistically significant, the clinical significance of this phenomenon is unclear, especially because this difference is not observed when using biopsy GG rather than RP specimen GG. Source of Funding: This work has been funded by the Sidney Kimmel Center for Prostate and Urologic Cancers, and the National Cancer Institute T32 CA082088-12 training grant (Sankin).