Effect of obesity on prostate‐specific antigen recurrence after radiation therapy for localized prostate cancer as measured by the 2006 Radiation Therapy Oncology Group‐American Society for Therapeutic Radiation and Oncology (RTOG‐ASTRO) Phoenix consensus definition

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Abstract
BACKGROUND.: Given the limited data regarding the impact of obesity on treatment outcomes after external beam radiation therapy (EBRT) for the definitive treatment of prostate cancer, the authors sought to evaluate the effect of obesity as measured by body mass index (BMI) on biochemical disease recurrence (BCR) using the most current 2006 Radiation Therapy Oncology Group‐American Society for Therapeutic Radiation and Oncology (RTOG‐ASTRO) Phoenix consensus definition (prostate‐specific antigen [PSA] nadir + 2 ng/mL).METHODS.: A retrospective cohort study identified men who underwent primary EBRT for localized prostate cancer between 1989 and 2003 using the Center for Prostate Disease Research (CPDR) Multi‐center National Database. BMI was calculated (in kg/m2) and the data were analyzed. Univariate and multivariate Cox proportional hazards regression analyses were used to determine whether BMI significantly predicted BCR.RESULTS.: Of the 1868 eligible patients, 399 (21%) were obese. The median age of the patients and pretreatment PSA level were 70.2 years and 8.2 ng/mL, respectively. Of 1320 patients for whom data were available with which to calculate PSA recurrence (PSA nadir + 2 ng/mL), a total of 554 men (42.0%) experienced BCR. On univariate analysis, BMI was found to be an independent predictor of PSA recurrence (P = .02), as was race, pretreatment PSA level, EBRT dose, clinical T classification, Gleason score, PSA nadir, and the use of androgen‐deprivation therapy (ADT). On multivariate analysis, BMI remained a significant predictor of BCR (P = .008).CONCLUSIONS.: To the authors' knowledge, this is the first study to report the association between obesity and BCR after EBRT for localized prostate cancer as measured by the updated 2006 RTOG‐ASTRO definition. A higher BMI is associated with greater odds of BCR after undergoing definitive EBRT. Cancer 2007. Published 2007 by the American Cancer Society.

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