Impact of acquired comorbidities on all-cause mortality rates among older breast cancer survivors.
BACKGROUND
Breast cancer survivors with higher numbers of comorbidities at the time of primary treatment suffer higher rates of all-cause mortality than comparatively healthier survivors. The effect of time-varying comorbidity status on mortality in breast cancer survivors, however, has not been well investigated.


OBJECTIVE
We examined longitudinal comorbidity in a cohort of women treated for primary breast cancer to determine whether accounting for comorbidities acquired after baseline assessment influenced the hazard ratio of all-cause mortality compared with an analysis using only baseline comorbidity.


METHODS
Cox proportional hazards adjusted for age, race/ethnicity, and exercise habits were modeled using (1) only a baseline Charlson index; (2) 4 Charlson index values collected longitudinally and entered as time-varying covariates, with missing values addressed by carrying forward the prior observation; and (3) the 4 longitudinal Charlson scores entered as time-varying covariates, with missing values multiply imputed.


RESULTS
The 3 modeling strategies yielded similar results; Model 1 HR: 1.4 per unit increase in Charlson index, 95% confidence interval (CI): 1.2-1.7; Model 2 HR: 1.3, 95% CI: 1.1-1.5; and Model 3 HR: 1.4, 95% CI: 1.2-1.6.


CONCLUSIONS
Our findings indicate that a unit increase in the Charlson comorbidity index raises the hazard rate for all-cause mortality by approximately 1.4-fold in older women treated for primary breast cancer. The conclusion is essentially the same whether accounting only for baseline comorbidity or accounting for acquired comorbidity over a median follow-up period of 85 months.
Ahern
Thomas P
TP
Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts 02118, USA. tpa@bu.edu
Lash
Timothy L
TL
Thwin
Soe Soe
SS
Silliman
Rebecca A
RA
D000368:Aged; D001943:Breast Neoplasms / Q000150:complications* / Q000401:mortality*; D002423:Cause of Death; D002908:Chronic Disease; D015897:Comorbidity; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D015141:Los Angeles / Q000453:epidemiology; D008910:Minnesota / Q000453:epidemiology; D009657:North Carolina / Q000453:epidemiology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012237:Rhode Island / Q000453:epidemiology; D012307:Risk Factors; D016019:Survival Analysis; D017741:Survivors / Q000706:statistics & numerical data*