Introduction:

About one third of prostate cancer (PCa) patients who undergo radical prostatectomy (RP) are upgraded between biopsy and RP. Improved prediction of upgrading is needed to inform treatment decisions. We investigated whether body mass index (BMI) is associated with upgrading in a large, multi-center study.

Methods:

We included 1,586 men with localized PCa who received RP as initial treatment within one year of biopsy in the Prostate Cancer Progression Study in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Using self-reported, pre-diagnostic BMI, we evaluated any upgrading compared to no change in Gleason score (GS), and separately analyzed upgrading in men with GS 6 at biopsy and GS 7 at biopsy. We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for BMI and upgrading, adjusting for age at diagnosis (continuous), race (white, non-white, missing), RP year (1994-2004 and 2005-2010) and smoking (never, former, current, missing). We ran separate models additionally adjusting for time from biopsy to RP to assess its potential role as a mediator of the association between BMI and upgrading. We also assessed interactions between BMI and age, race, RP year and smoking. We computed p-values for interaction using likelihood ratio tests comparing nested models with and without the interaction terms.

Results:

Upgrading occurred in 27.2% of our study population. The median age of PCa diagnosis was 66 years for both men who were upgraded and those who were not, with an age range of 55-84 years. The majority of men in our sample were white (90.1%). About 60.8% of the men had a clinical T stage of T1, and 39.2% had T2 disease. Most of the men in our sample had a prostate-specific antigen (PSA) concentration <10 ng/mL at diagnosis (77.7%). There tended to be a longer time between biopsy and surgery for those who were upgraded (median=56 days) than those who were not (median=54 days; Wilcoxon p-value=0.08). Comparing obese to normal weight men, we observed borderline significantly increased odds of any upgrading (OR=1.24, 95% CI: 0.90-1.70) and upgrading from GS 6 to 7 or greater (OR=1.34, 95% CI=0.91-1.97), but no association for GS 7 to 8 or greater (OR=1.49, 95% CI=0.70-3.19). Additional adjustment for time from biopsy to RP did not appreciably alter the results (OR for any upgrading=1.24, 95% CI=0.90-1.71). We observed some evidence of differences in the association between obesity and upgrading by RP year, with a positive association for men who underwent RP in 1994-2004 (OR for any upgrading=1.41, 95% CI=0.97-2.04), but not for 2005-2010 (OR=0.82, 95% CI=0.44-1.55; p-interaction=0.05). There were no differences by age, race or smoking (p-interaction=0.63, 0.88 and 0.54, respectively).

Conclusion:

Our results suggest a positive association between obesity and upgrading, which could not be explained by a delay in the time from biopsy to surgery and may in part reflect increased disease progression associated with obesity. These findings may help inform the patient-provider treatment decision making process.

Funding: N/A