Braun et al. BMC Cancer 2011, 11:353 http://www.biomedcentral.com/1471-2407/11/353 the patients into those who have received definitive can- cer treatment elsewhere before coming to our institution and those who were newly diagnosed at the time of pre- sentation to our institution. These data were obtained from the tumor registries of MRMC and SRMC. Data Analysis and Statistical Methods Patient survival was the primary end point and defined as the time interval between the date of first patient visit to the hospital and the date of death from any cause or the date of last contact/last known to be alive. The overall survival was calculated using the Kaplan-Meier or product-limit method. Clinical and QoL variables were also evaluated using univari- ate Cox regression analyses to determine which para- meters showed individual prognostic value for survival. Multivariate Cox regression analyses were then performed to evaluate the joint prognostic signif- icance of those QoL and clinical factors that were shown to be prognostic in univariate analyses. We used both forward stepwise method as well as the block entry method (all variables entered together at the same time in one block). Forward stepwise method was used because, as is common in QoL data, many of the individual QoL scales are highly corre- lated. Stepwise regression avoids the problem of mul- ticollinearity because two highly correlated attributes will normally not both be entered in the model. Since the global QoL scale of the QLQ-C30 is highly corre- lated with other scales, it was not included in prog- nostic indicator analyses when other variables from QLQ-C30 were used, in order to achieve model stabi- lity [28]. Instead, global QoL was analyzed separately after adjusting for clinical and demographic factors. Separate analyses stratified by prior treatment history were conducted to identify QoL factors prognostic of survival in both newly diagnosed and previously trea- ted patients. Cox regression with time-invariant covariates assumes that the ratio of hazards for any two groups remains constant in proportion over time. We checked this assumption by first examining log-minus-log plots for the categorical predictors and then fitting a Cox regres- sion with a time-varying covariate for each predictor in turn. Each QLQ-C30 scale was treated as a continuous variable for the purpose of Cox regression analyses. The effect of QoL parameters on patient survival was expressed as Hazard Ratios (HRs) with 95% confidence intervals (CIs). Pearson’s correlation coefficients were used to investigate the association between different QoL variables. An effect was considered to be statisti- cally significant if the p value was less than or equal to 0.05. All data were analyzed using SPSS version 17.0 (SPSS, Chicago, IL, USA). Page 3 of 9 Table 1 Baseline characteristics of 1194 lung cancer patients Characteristic Categories Number Percent Age at presentation (years) ■ Mean 58.3 ■ Median 58.5 ■ Range 21.6-86.4 Gender ■ Male 601 ■ Female 593 Tumor Stage at Diagnosis ■ Stage 1 100 ■ Stage 2 63 ■ Stage 3 348 ■ Stage 4 656 ■ Indeterminate 27 Vital Status ■ Expired 778 ■ Alive 416 Treatment History ■ Newly diagnosed 605 ■ Previously treated 589 50.3 49.7 8.4 5.3 29.1 54.9 2.3 65.2 34.8 50.7 49.3 Results Patient characteristics Table 1 describes the baseline characteristics of our patient cohort while Table 2 provides descriptive statis- tics for the population from the QLQ-C30 scale scores. Among the QLQ-C30 functioning scales, role function- ing had the lowest (worst) mean score of 58.9 while the highest (best) mean score of 74.9 was recorded for cog- nitive functioning. Among the QLQ-C30 symptom scales, diarrhea had the lowest (best) mean score of 9.9 while the highest (worst) mean score of 46.8 was recorded for fatigue. Relationship between QoL and other covariates Table 3 describes the distribution of QoL scores by stage of disease and prior treatment history using 2 Table 2 Baseline QoL scores of 1194 lung cancer patients Mean Median QLQ-C30 Scale Global Physical Role Emotional Cognitive Social Fatigue Nausea/Vomiting Pain Dyspnea Insomnia Appetite Loss Constipation Diarrhea 53.6 68.7 58.9 64.1 74.9 61.2 46.8 14.5 37.1 37.6 39.9 31.3 24.2 9.9 58.3 73.3 66.7 66.7 83.3 66.7 44.4 0 33.3 33.3 33.3 33.3 0 0 SD 26.3 25.5 34.3 25.8 25.9 32.9 28.4 22.2 32.8 33.6 33.5 34.1 31.3 19.7 Range 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 0-100 Higher scores in the global and functioning scales and lower scores in the symptom scales indicate better QoL.