Comorbidity and body mass index (BMI) as predictors of survival for African Americans and Caucasians following surgery for adenocarcinoma of the colon

Abstract

There is a survival disparity between African Americans and Caucasians having colon cancer. Among the reasons given as possible causes for the increased risk of death in African Americans following a diagnosis of colon cancer are comorbidity and body habitus. The primary question this dissertation sought to answer was whether or not comorbidity and/or BMI could account for any of the increased risk of death seen in African Americans with colon cancer. However, before answering this question, the matter of which comorbidity index to use in assessing the comorbidity burden in this population of colon cancer patients had to be addressed.

The study population consisted of colon cancer patients (n = 496) who underwent surgery at the University of Alabama at Birmingham (UAB) Hospital from 1981-2002. In the first manuscript, hazard ratios (HR) with 95% confidence intervals (CI) were obtained by Cox proportional hazards models for the three comorbidity indices and the association with death. In the second manuscript, hazard ratios were obtained for the association of race, comorbidity, BMI, and covariates with mortality. The confounding influence of comorbidity and BMI for the increased risk of death associated with African American race was evaluated. Effect modification by tumor stage and race was also assessed.

In the comparison of the three comorbidity indices, the highest comorbidity burden for each index was significantly associated with poorer overall survival (ACE-27: HR = 1.63, 95% CI, 1.24-2.15; NIA/NCI: HR = 1.83, 95% CI, 1.29-2.61; CCI: HR = 1.46, 95% CI, 1.14-1.88). For BMI, with those of normal weight serving as the referent group, being underweight increased the risk of death (HR = 1.54; 95% CI, 0.96-2.45) while being overweight/obese was protective (HR = 0.77; 95% CI, 0.61-0.97). After adjustment for comorbidity, BMI, and other risk factors, African American race was still associated with a 34% increased risk of death relative to Caucasians (HR = 1.34; 95% CI, 1.06-1.68).

Comorbidity and BMI are both associated with death following surgery for colon cancer. However, neither comorbidity nor BMI accounts for any of the excess mortality associated with African American race.