Four variables were used as measures of the neighborhood socioeconomic status: 1) median income; 2) proportion of employment; 3) proportion separated, divorced, or widowed; and 4) proportion not graduated from high school. Exploratory data analysis was performed to determine cutoff levels for categorical variables. Descriptive statistics were calculated for the overall cohort with respect to patient and clinical characteristics. Chi-square or Fisher exact tests, as appropriate, were used to assess associations between patient/clinical characteristics and the timing of receiving chemotherapy. Metabolism inhibitor
The patient and clinical characteristics that were evaluated included sex, age at diagnosis, region of residence at diagnosis, neighborhood socioeconomic selleck chemical
factors, number of comorbidities, and year of diagnosis. Time from the date of surgery to the date of first chemotherapy session was calculated, and patients were categorized into the following 4 groups for survival analysis: received chemotherapy 1) within 8 weeks after surgery, 2) 8 to 12 weeks after surgery, 3) 12 to 16 weeks after surgery, or 4) no treatment within 16 weeks. The last group originally was separated into ��received chemotherapy >16 weeks�� and ��never received chemotherapy.�� In the final analysis, these 2 groups were combined, because the hazard ratios (HRs) for these 2 groups relative to the reference group (<8 weeks) were very similar. Kaplan-Meier curves were used to describe the patient survival stratified <a href="http://www.selleck.cn/products/Rapamycin.html
">Rapamycin by time from surgery to adjuvant chemotherapy. Cumulative incidence curves were used to describe the cumulative mortality from colon cancer-specific deaths, treating the other causes of death as competing risk.14 The Kaplan-Meier and cumulative incidence curves were started at 16 weeks after surgery. This starting time was the earliest time point that allowed us to define all ��time from surgery to adjuvant chemotherapy�� groups before the starting time: Deaths before this starting time were not included in the analysis. Cox proportional hazards models were used to estimate the adjusted colon cancer-specific and overall mortality HRs according to the time from surgery to adjuvant chemotherapy (time-dependent covariate) starting at 16 weeks after surgery. The following covariates were included in the Cox regression models to adjust for relevant factors related to survival to produce adjusted HR estimates for the time-to-adjuvant-treatment variable: sex, age at diagnosis, region of residence at diagnosis, number of comorbidities, year of diagnosis, and neighborhood-level socioeconomic factors. To closely adjust for age at diagnosis, a natural cubic spline of age at diagnosis was used with 4 knots.15P values for the time to adjuvant chemotherapy and year of diagnosis were calculated based on a trend test with 1 degree of freedom. Patients were followed to the earlier of death or March 31, 2009.