Subcutaneous Adipose Tissue Characteristics and Risk of Biochemical Recurrence in Men with High Risk Prostate Cancer

Abstract

Obesity has become a worldwide epidemic. The interaction of obesity and excess adipose tissue on cancer biology continues to be an area of interest. The purpose of this study was to assess subcutaneous adipose tissue characteristics by computed tomography (CT) as potential imaging biomarkers in patients with high risk prostate cancer receiving radiation treatment (RT). This retrospective study included 185 men with high risk prostate cancer (PSA>20 ng/mL, Gleason score ≥ 8, or clinical extraprostatic extension) treated between 2001 and 2012. All patients received definitive, dose-escalated external beam RT along with a course of neoadjuvant, concurrent, and adjuvant androgen deprivation therapy (ADT). Each patient also had a treatment planning CT that included the L4-L5 vertebral interface and prostate specific antigen (PSA) measurements for at least 1 year following RT. The subcutaneous adipose tissue was contoured on a single axial CT slice at the level of L4-L5. The average CT attenuation, in Hounsfield units (HU), of the structure was calculated and defined as SATHU. SATAREA was defined as the cross-sectional area of the structure (in cm2) that was then normalized by the square of patient height. Biochemical failure (BF) was defined as a PSA rise of 2 ng/mL from the nadir. Freedom from BF (FFBF) was calculated from start time of ADT using the Kaplan-Meier method. Estimates of FFBF were stratified by SATHU and SATAREA quartiles. Median follow-up was 5.3 years. The mean SATHU (± standard deviation) was -99.2 HU (±6.3 HU) and the mean SATAREA was 94.7 cm2/m2 (±42.3 cm2/m2). No significant differences of SATHU and SATAREA were observed among different races or age groups. The 5 and 8-year rates of FFBF across all patients were 82.1% and 74%, respectively. Patients in the lowest quartile of SATHU experienced significantly higher FFBF compared to the other quartiles (Q4 vs. Q1, p=0.029; Q4 vs. Q2, p=0.045; Q4 vs. Q3, p=0.045). No other differences in FFBF were observed between quartiles of SATAREA or other quartiles of SATHU. Using CT imaging as a novel prognostic biomarker, low attenuation of abdominal adipose tissue was associated with a lower rate of biochemical failure in patients with high risk prostate cancer. Further research is needed to elucidate the biological underpinnings of this clinical finding and the role adipose tissue plays in modulating oncologic behavior and outcomes.