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Department of Surgery, Division of Thoracic and Cardiovascular Surgery, University of Virginia Health System, Charlottesville, Virginia
Accepted for publication April 11, 2011.
* Address correspondence to Dr Lau, Department of Surgery, University of Virginia School of Medicine, PO Box 800679, Charlottesville, VA 22908 (Email: cll2y{at}virginia.edu).
Presented at the Poster Session of the Forty-seventh Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 31–Feb 2, 2011.
| Abstract |
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Methods: From 2003 to 2007, 129,207 patients undergoing lung cancer resections were evaluated using the Nationwide Inpatient Sample (NIS) database. Multiple regression analysis was used to estimate the effects of gender, race, and socioeconomic status on risk-adjusted outcomes.
Results: Average patient age was 66.8 ± 10.5 years. Women accounted for 5.0% of the total study population. Among racial groups, whites underwent the largest majority of operations (86.2%), followed by black (6.9%) and Hispanic (2.8%) races. Overall the incidence of mortality was 2.9%, postoperative complications were 30.4%, and pulmonary complications were 22.0%. Female gender, race, and mean income were all multivariate correlates of adjusted mortality and morbidity. Black patients incurred decreased risk-adjusted morbidity and mortality compared with white patients. Hispanics and Asians demonstrated decreased risk-adjusted complication rates. Importantly low income status independently increased the adjusted odds of mortality.
Conclusions: Female gender is associated with decreased mortality and morbidity after lung cancer resections. Complication rates are lower for black, Hispanic, and Asian patients. Low socioeconomic status increases the risk of in-hospital death. These factors should be considered during patient risk stratification for lung cancer resection.
| Introduction |
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Disparities in medical and surgical outcomes are often influenced by several patient- and health system–related factors. Patient outcomes after surgical lung cancer resection may be related to inherent differences in gender, race, or socioeconomic status. Although other reported series have identified these factors as potential determinants of patient outcomes and survival [3–13], many of these reports are limited by single institutional experiences or statewide databases. In addition many published analyses lack critical social- and hospital-related data required for rigorous risk adjustment and are subject to biases that limit their generalizability to patients nationwide.
The present study used a nationwide administrative database to examine the influence of gender, race, and socioeconomic status on risk-adjusted morbidity and mortality after appropriate adjustment for various demographic, social, operation, and institutional factors. Understanding the independent influence of these variables is critical to reducing disparities in lung cancer care and identifying methods to improve patient outcomes.
| Material and Methods |
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The University of Virginia Institutional Review Board (IRB) exempted this study from formal review because it failed to meet the regulatory definition of human subject research because of the lack of controlled patient identifiers and because the data is not collected for research purposes only.
Patients and Hospitals
A total of 26,189 discharge records representing a weighted estimate of 129,207 patients undergoing lung cancer resections was identified by querying the first 5 diagnosis and procedure categories with the NIS using the following International Classification of Diseases—Ninth Revision, Clinical Modifications (ICD-9-CM) procedure and diagnostic codes: lung resection (ICD-9-CM codes 323, 3230, 3239, 324, 3241, 3249, 325, 3250, 3259) and primary diagnosis of lung cancer (ICD-9-CM codes 162, 1622, 1623, 1624, 1625, 1628, 1629). The presence of patient admission-level comorbid disease was assessed using available Agency for Health Research and Quality comorbidity categories within the NIS datasets developed by Elixhauser and colleagues [14]. Hospital-related details were available within the NIS database. Thoracic surgery teaching hospital status was determined by linking the American Hospital Association identification numbers of all hospitals within the NIS study dataset with hospital reports from the Association of American Medical College's Graduate Medical Education tracking system. Hospital operative volume was categorized into quartiles: low (< 25th percentile), medium (26th to 49th percentile), high (50th to 74th percentile], and very high (> 75th percentile].
Outcomes Measured
All measured outcomes were established a priori. The primary outcomes in this study were the effects of gender, race, and socioeconomic status on risk-adjusted mortality and morbidity after lung cancer resections. Secondary outcomes of interest included observed differences in the overall incidence of mortality and postoperative complication rates. The incidence of postoperative and pulmonary complications was determined using previously described methodology [15, 16].
Statistical Analysis
All statistical methodology used in this study was designed to test the null hypothesis that risk-adjusted outcomes after lung cancer resections in the United States are not significantly different with respect to gender, race, and socioeconomic status. Statistical significance for all analyses was defined by an alpha of less than 0.05. Because of the complex sampling methods used by the NIS, all data analyses were performed using Predictive Analytics SoftWare (PASW) Statistics version 18.0.0 complex samples module (IBM Corporation, Somers, NY).
Descriptive Statistics and Univariate Analyses
Descriptive and inferential statistics were used to compare observed differences in the incidence of mortality, composite postoperative complication rate, and pulmonary complication rate as a function of gender, race, and mean income. Continuous variables with normal distributions are reported as means ± standard deviation, whereas the median (interquartile range) is used to express nonnormally distributed data. Continuous variables were compared using either the Student's t test or the Mann-Whitney U test. Comparisons of categorical variables used the Pearson's
2 or Fisher's exact test where appropriate. All categorical variables are expressed as a percentage of the total study population or respective study group. Independent sample group comparisons were unpaired. All calculated test statistics were used to derive reported 2-tailed p values. Two additional effect size statistics were calculated to provide an estimate of the strength of the relationship between 2 variables within a given population and to provide a clinically practical interpretation of the reported results The phi coefficient was calculated for all univariate comparisons with 1 degree of freedom, and the Cramer's V statistic was computed for comparisons of categorical ordinal variables with greater than 1 degree of freedom.
Multivariable Analysis
Because of the complex structure of this study dataset, hierarchical multiple logistic regression was used to estimate risk-adjusted associations between female gender, race, and mean income quartile and the outcomes of in-hospital death, composite incidence of postoperative complications, and pulmonary complications for patients undergoing lung cancer resections. Three separate logistic regression models were used for each outcome. Missing data for individual covariates accounted for less than 5% of the total study dataset. All covariates considered potential confounders for model outcomes were selected a priori and were retained in each final model. The predictive strength and relative contribution of each model covariate was assessed by the Wald
2 statistic. Results of each logistic regression model are reported as confounder adjusted odds ratio (AOR) with 95% confidence interval (CI). Model performance was assessed by the area under the receiver operating characteristics curve (AUC) and the Nagelkerke Pseudo R
2 statistic. Sensitivity analyses were performed by reestimating each model after removing the strongest individual predictor as determined by the Wald statistic [17]. Using this technique, model performance is validated if the observed effects remain statistically significant and are not substantially attenuated (> 10%) after reestimation.
| Results |
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2 statistics when compared with the effect of race. With respect to postoperative complications, female gender was a significant positive predictor of any postoperative complication (AOR = 0.83) as well as pulmonary complications (AOR = 0.93) after lung cancer resection. Among racial groups, black, Hispanic, and Asian patients incurred decreased risk-adjusted complication rates compared with white patients. No significant associations were observed for the effect of income on the odds of postoperative complications.
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| Comment |
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In this study, the effect of gender was a significant correlate of postoperative mortality and morbidity and is in agreement with other reported series [3, 4, 8, 10, 11]. In 1 recent series reporting on outcomes from the national Society of Thoracic Surgeons (STS) General Thoracic Surgery Database, male gender was associated with elevated odds of mortality (OR = 1.37; p = 0.013) as well as the composite outcome of mortality and major morbidity (OR = 1.12; p = 0.031) after lung cancer resections [3]. Furthermore the beneficial effects of female gender on 5-year survival rates for women with stage I/III tumors were noted in another prospective series of 1,085 patients with non-small cell lung carcinoma [8]. Important to consider in the results of the present study is the relative disproportion of females to males within this NIS dataset as well as the relative strength of female gender as an independent risk factor for the primary outcomes of interest. Considering the estimated associations between female gender and outcomes, we would expect that the effect of female gender on risk-adjusted outcomes may be even more dramatic in datasets with more equal distribution of gender. Moreover although not directly assessed in the present study, the influences of tumor type and disease stage must be considered as contributing to the improved perioperative outcomes for women undergoing lung cancer resections.
The present results provide a valuable extension to accumulated data regarding the influence of race and socioeconomic status on lung cancer treatment and outcomes [5–7, 13, 18]. In a recent population-based study of 76,086 lung cancer resection patients (1998 to 2002) within a Florida cancer registry, black patients were diagnosed with lung cancer at an earlier age and with more advanced disease. They composed the largest proportion of low-income patients and were less likely to undergo surgical resection, which resulted in reduced median survival times compared with whites (7.5 years vs. 8.8 years; p < 0.001) [13]. However after risk-factor adjustment, race failed to be a multivariate correlate of survival in this series, whereas severe poverty was an independent predictor of worse survival (HR = 1.05; p = 0.001). Importantly in this series no significant differences were observed for patients undergoing surgical resections, and the study is limited by the fact that only 22% of their cohort underwent surgical resection, their analysis failed to address postoperative morbidity, and the results reflect trends that may not be current. Other series however corroborate these findings among single institutional experiences and various cancer registries and are complementary to those of the present analysis [5, 18].
The potential explanations for disparities in outcomes related to gender, race, and socioeconomic status in this study are complex and multifactorial. Substantial evidence exists describing the interaction of various factors on patient outcomes, including ethnicity, education level, language barriers, socioeconomic status, cultural values, poor physician-patient communication, provider bias, disparities in hospital resource use, and access to specialized care [16, 19–24]. In this large observational analysis, we also demonstrate the independent influence of several of these factors. Specifically these results indicate that many of the racial and socioeconomic influences that have been documented as potential culprits for disparities in patient outcomes appear related. When individually accounted for through regression analysis, various modifiable social, health system, and economic factors largely account for the observed differences. In fact these data, as well as those presented elsewhere [5, 18], demonstrate that many ethnic disparities in lung cancer outcomes could be reduced, and even improved, with appropriate use of operative intervention and adjuvant therapy.
The presented results are subject to select limitations. Because of the retrospective study design, selection bias must be considered. In addition we are unable to account for certain data, including tumor type, pathologic or clinical stage, preoperative performance status, or predicted pulmonary function. Use of community-level income status, such as mean income by ZIP code, is admittedly imperfect, and this definition of socioeconomic status may differ compared with other studies. However previous research has supported the use of such definitions as a valid proxy for socioeconomic status [25–28]. The use of de-identified data and the lack of long-term follow-up within the NIS limits the ability to scrutinize the data further, and this study also did not directly examine the effects of insurance or primary payer status on risk-adjusted outcomes. The impact of varying insurance types on risk-adjusted outcomes however has been documented in other recent surgical series [16, 29]. Despite these limitations, use of the NIS provides important benefits because the data represented is broadly applicable to patients nationwide and allows for the effective adjustment for certain social and economic influences that are often poorly captured or unavailable in other institutional or registry datasets.
Conclusions
The results reported herein demonstrate important differences in lung cancer resection outcomes as they relate to disparate differences in gender, race, and socioeconomic status. Based on these analyses, female gender is associated with decreased risk-adjusted mortality and morbidity after lung cancer resection, whereas the odds of postoperative complications are lower for black, Hispanic, and Asian patients. Low socioeconomic status increases the risk of in-hospital death. These factors should be considered during individual patient risk stratification for lung cancer resection, and optimization of modifiable patient-, provider-, and system-related factors may help to reduce health disparities and outcomes for this patient population.
| Acknowledgments |
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| References |
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This article has been cited by other articles:
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D. J. LaPar, C. M. Bhamidipati, C. L. Lau, D. R. Jones, and B. D. Kozower The Society of Thoracic Surgeons General Thoracic Surgery Database: Establishing Generalizability to National Lung Cancer Resection Outcomes Ann. Thorac. Surg., July 1, 2012; 94(1): 216 - 221. [Abstract] [Full Text] [PDF] |
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