Obesity and Risk of Biochemical Failure for Patients Receiving Salvage Radiotherapy After Prostatectomy

Purpose: Obesity has been proposed as an independent risk factor for patients undergoing surgery or radiotherapy (RT) for prostate cancer. Using body mass index (BMI) as a measure of obesity, we tested its role as a risk factor for patients receiving salvage RT after prostatectomy. Methods and Materials: Rates of subsequent biochemical relapse were examined in 90 patients who underwent salvage RT between 1984 and 2004 for biochemical failure after radical prostatectomy. Median follow-up was 3.7 years. The BMI was tested as a continuous and categorical variable (stratified as <25, 25-<30, and ≥30 kg/m²). Univariate and multivariate proportional hazards regression analyses were performed for clinical, pathologic, and treatment factors associated with time to relapse after salvage RT. Results: There were 40 biochemical failures after salvage RT with a median time to failure of 1.2 years. The BMI was not associated with adverse clinical, pathologic, or treatment factors. On multivariate analysis, obesity was independently significant (hazard ratio [HR], 1.2; p = 0.01), along with RT dose (HR, 0.7; p = 0.003) and pre-RT prostate-specific antigen level (HR, 1.2; p = 0.0003). Conclusions: This study is weakly suggestive that obesity may be a risk factor for salvage RT patients. Whether this results from greater biologic aggressiveness or technical inadequacies cannot be answered by this study. Given the very high failure rate observed for severely obese patients, we propose that technical difficulties with RT are at play. This hypothesis is supported by the RT literature and could be prospectively investigated. Techniques that optimize targeting, especially in obese patients, perhaps seem warranted at this time.