Abstract A75: An analysis of the interaction between obesity and measures predicting prostate cancer-free survival
Authors: Hudson Aaron , Zeigler-Johnson Charnita , Glanz Karen , Spangler Elaine , Rebbeck Timothy R. , Morales Knashawn H. 
Published: May 2016

Introduction: Obesity has been associated with recurrence of prostate cancer for treated patients in past research. The Kattan nomogram and the CaPSURE/CPDR recurrence equation have been developed to approximate the probability that prostate cancer will recur in a patient after radical prostatectomy. Although these are commonly used algorithms, it is not clear how well they predict disease recurrence in obese patients. The purpose of this project is to examine whether obesity modifies the association between prostate cancer outcomes and the two prediction scores. We hypothesized that there will be differences among BMI groups in associations between prediction scores and prostate cancer recurrence. This would suggest varying accuracy in post-operative prognoses for radical prostatectomy patients by obesity status.

Methods: Our sample included 1576 radical prostatectomy patients. Patients' obesity was classified using BMI as per conventional standards. The Kattan score was calculated using preoperative clinical variables and post-treatment pathologic variables, and the CaPSURE/CPDR score was calculated using a subset of these variables in addition to race. Cutoff points were defined for each score, and patients were categorized into low, medium, and high risk groups. Time to prostate cancer recurrence was modeled using Cox proportional hazard models as a function of obesity, the predictive score risk group, and their interaction. The models were adjusted for patients' age in addition to other measures associated with failure but not used to calculate the score.

Results: As expected for the Kattan score, estimated hazard ratios (95% CI) indicated higher rates of recurrence for the medium (2.99 (2.29, 3.88)) and high (8.84 (5.91, 13.2)) risk groups compared to the low risk group. The associations were not statistically different across obesity groups. However, we noticed within our sample that the association between obesity and prostate cancer was strong in the low risk group and weak in the high risk group. Results were consistent for the CaPSURE/CPDR score.

Conclusion: We observed no difference in the association between cancer recurrence and prediction scores across different obesity groups. However, we did observe that the relationship between obesity and cancer recurrence was stronger for low risk patients than for high risk patients, with obese men in the low risk group having poorer outcomes. This suggests that when men are at a high risk of cancer recurrence, obesity is a less effective predictor of recurrence, but obesity should be taken into account when predicting prostate cancer outcomes for moderate to low risk men. These results are not statistically significant. Our study suffered from a small sample of high risk patients, so there is not sufficient evidence that our findings are generalizable to all radical prostatectomy patients.

Citation Format: Aaron Hudson, Charnita Zeigler-Johnson, Karen Glanz, Elaine Spangler, Timothy R. Rebbeck, Knashawn H. Morales. An analysis of the interaction between obesity and measures predicting prostate cancer-free survival. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr A75.