Ethnic Disparities in the Treatment of Stage I Non-small Cell Lung Cancer Juan P. Wisnivesky, MD, MPH, Thomas McGinn, MD, MPH, Claudia Henschke, PhD, MD, Paul Hebert, PhD, Michael C. Iannuzzi, MD, and Ethan Halm, MD, MPH Online Data Supplement
Methods The Surveillance, Epidemiology and End Results (SEER) Program is a national database that has been collecting data on all incident cancer cases in selected geographic areas of the US since 1973. This registry contains information on the date of diagnosis, the location, histologic type, stage at diagnosis, and type of treatment provided. The SEER Program encompasses nearly 14% of the total US population and about 22% of the US Hispanic population (E1). We identified all cases of non-small-cell lung cancer (tumor site codes 34.0-34.9 and ICD-O-2 morphology codes 8010-8040, 8050-8076, 8140, 8143, 8250-8260, 8310, 8320, 8323, 8470-8490, 8550-8573), diagnosed prior to autopsy from the SEER registry 2003 (E1). This study included 119,928 cases that were diagnosed as having a first invasive cancer during last decade reported in SEER (1991 to 2000). We excluded cases that had not undergone a complete evaluation to determine the stage of disease or for whom there was no documentation of survival in the SEER data (23,211 cases). Among these subjects, we identified cases of Stage I cancer by the American Joint Committee on Cancer (E2): T1 (SEER tumor extent code 10) or T2 (SEER tumor extent code 20 and 40), N0 (SEER lymph node code 0), and M0 (SEER tumor extension less than 40). We found 19,160 Stage IA (T1N0M0) or Stage IB (T2N0M0) cases that were potentially eligible. From this group we identified 16,036 subjects classified as white or Hispanic.
Cases were classified as resected if the SEER site-specific variable indicated that a surgical procedure (local resection, segmentectomy, wedge resection, lobectomy, and partial or total pneumonectomy [SEER codes 10 to 70]) had been performed. Cancer site and morphology were coded according to the International Classification of Diseases for Oncology, Second Edition (E3). The cause of death provided in the SEER registry is abstracted from the National Center for Health Statistics database of consolidated death certificates from Vital Statistics Office in each state. Information about age at diagnosis, sex, race, marital status, and area of residence was obtained from SEER. Statistical Analysis The Kaplan-Meier method was used to estimate survival rates (E4). First, we compared the overall (all case mortality) survival proportions for Hispanics and whites. A proportion of patients with lung cancer however, dies of unrelated causes. Since the purpose of the study was to evaluate disparities in the treatment of lung cancer, we used lung-cancer specific mortality for all other comparisons, since it allows for controlling for unrelated causes of death. To estimate cancer-specific survival rates, deaths attributed to causes other than lung cancer were censored at the date of death. Survival curves were compared using the log-rank statistic. All reported p-values are two sided using a significant level of 0.05.
To evaluate whether differences in the rate of surgical treatment between Hispanics and whites were attributable to unbalances in the distribution of coexisting illnesses, survival curves were constructed considering only deaths from causes other than lung cancer as an event (non-lung cancer survival). In these analyses, deaths due to lung cancer were treated as random censored observations. When stratifying by ethnicity, these survival curves represent the overall burden of comorbid conditions influencing survival in an ethnic group. If, for example, the rate of surgical treatment for Hispanics is lower as a consequence of a higher prevalence of serious comorbid conditions that preclude resection, the non-lung cancer survival would be expected to be lower among Hispanics than whites. Adjusted associations between ethnicity and mortality risk were evaluated using the Cox proportional hazard regression model (E5).
References E1. Suveillance, Epidemiology and End Results (SEER) Program Public-Use Data (1973-2000). Washington, DC: National Cancer Institute, DCCPS, Surveillance Research Program, Cancer Statistics Branch, released April 2003. E2. Mountain CF. Revisions in the International System for Staging Lung Cancer. Chest. 1997;111(6):1710-1717. E3. Percy C, V. H. V., Muir C, editors. 1990. International Classification of Diseases for Oncology, 2nd Edition ed. Geneva, Switzerland, World Health Organization. E4. Kaplan EL, M. P. 1958. Nonparametric estimation for incomplete obserbations. J Am Stat Assoc 53:457-81. E5. Hosmer DW, L. S. Applied Survival Analysis. Regression Modeling in Time to Event Data. New York: J Wiley; 1999: 87-112.