Comparative Study of Survival among Small Cell Lung Cancer Patients in the U.S. Military Health System and Those in the Surveillance, Epidemiology, and End Results (SEER) Program

Abstract

Purpose:

The U.S. military health system (MHS) provides universal health care access to beneficiaries. However, whether the universal access has translated into improved patient outcome is unknown. We compared survival of small-cell lung cancer (SCLC) patients in the MHS with that in the U.S. general population. Stage and receipt of cancer treatment were also compared to see if they could contribute to survival difference.

Methods:

The data were obtained from The Department of Defense’s (DoD) Automated Central Tumor Registry (ACTUR) and the national Surveillance, Epidemiology, and End Results (SEER) program, respectively. ACTUR (N=3,040) and SEER patients (N=12,160) were matched on age, sex, race and diagnosis year. Multivariable Cox regression model was used to compare all-cause mortality between ACTUR and SEER. Multivariable logistic regression was performed to compare cancer stage and treatment.

Results:

ACTUR patients exhibited significantly better survival than SEER counterparts (HR = 0.77, 95% CI= 0.71–0.83). ACTUR and SEER patients had similar stage, but ACTUR patients were more likely to receive radiation treatment (OR=1.26, 95% CI=1.12–1.42). The survival advantage of ACTUR patients remained across all tumor stages and radiation groups.

Conclusions:

SCLC patients with universal health care access had better survival than similar patients in the U.S. general population. Future studies are warranted to identify factors that may contribute to the improved survival.

Introduction

Access to health care, as reflected by health insurance, is an important factor influencing survival of lung cancer patients.[1–6] Studies have shown that lung cancer patients without health insurance or with Medicaid had higher mortality than patients with private insurance or Medicare.[1–6] Accessibility to health care affects multiple factors contributing to lung cancer survival, such as early diagnosis, receipt of treatments and quality of care delivered.[1–6]

The U.S. military health system (MHS) provides universal access to health care for 9.6 million beneficiaries, including service members of the seven uniformed services, National Guard and Reserve members, retirees, and their family members.[7] As the beneficiaries receive health care free of charge or with minimal out-of-pocket cost,[7] barriers to health care access are largely reduced. We previously showed that MHS beneficiaries with non-small cell lung cancer (NSCLC), the most common type of lung cancer accounting for 85–90% of lung cancers, had better survival than their counterparts in the U.S. general population,[8] supporting the beneficial role of universal health care in improving survival of NSCLC patients.

Small-cell lung cancer (SCLC) constitutes only 10% to 15% of lung cancer cases,[9] but has the worst prognosis of all pulmonary tumors with a five-year survival rate of only 6.6%, compared to 16.9% of all lung cancers. [10] Expanding our previous study on NSCLC,[8] in the current study, we compared overall survival of SCLC patients in the MHS with that in the U.S. general population. We hypothesized that MHS patients with SCLC would have better survival than SCLC patients in the U.S. general population as a benefit of universal medical care provided by the MHS. Since cancer stage at diagnosis and treatment receipt are important predictors of survival and related to health care accessibility, potentially contributing to the survival difference, we also compared tumor stage and receipt of therapy between the two populations to assess their potential effects on the survival difference.

Materials and Methods

Data Sources

The data for this study were from the Department of Defense’s (DoD) Automated Central Tumor Registry (ACTUR) and the National Cancer Institute’s (NCI) Surveillance, Epidemiology, and End Results (SEER) program. ACTUR collects information on cancer diagnosis and treatment of MHS beneficiaries who are diagnosed or treated at military treatment facilities (MTFs). MTFs are required to report to ACTUR the data on demographics, tumor characteristics, cancer treatment, follow up, vital status and other information. ACTUR complies the data according to the guidelines of the North American Association of Central Cancer Registries (NAACCR).[11]

Cases from the U.S. general population were identified from the National Cancer Institute’s (NCI) Surveillance, Epidemiology, and End Results (SEER) program. The SEER program is collection of cancer registries from around the US that contains data on patient demographics, tumor characteristics, first course of treatment, follow up, vital status and other information within the areas served by the SEER registries. In this study, the SCLC cases were identified from the SEER 18 registries. The SEER data started in 1975 covering nine areas and expanded to more areas over time. This study used SEER 18 that started in 2000, which also contains case data from earlier SEER databases[12]. For this study, the data from 1987 when the ACTUR data became available, were used. The catchment of SEER 18 registries (Atlanta, Connecticut, Detroit, Hawaii, Iowa, New Mexico, San Francisco-Oakland, Seattle-Puget Sound, Utah, Los Angeles, San Jose-Monterey, Rural Georgia, the Alaska Native, Greater California, Greater Georgia, Kentucky, Louisiana, and New Jersey) represents about 28% of the U.S. general population. [13]

This study, based on non-identifiable ACTUR data, was approved by the institutional review boards of Walter Reed National Military Medical Center and Uniformed Services University of the Health Sciences. SEER data are de-identified for public use.

Study Population

SCLC was identified using topography codes (C34.0 to C34.3, C34.8, C34.9) and morphology codes (8041 to 8045) according to the International Classification of Diseases for Oncology, third edition (ICD-O-3).[14] Eligible cases from both ACTUR and SEER were patients with histologically confirmed SCLC between January 1, 1987 and December 31, 2012. Cases with diagnoses from death certificate or autopsy were excluded. Cases with multiple primary tumors were excluded to minimize effects of other cancers on the study outcome. Multiple primary tumors are defined by SEER coding rules. [15] We processed ACTUR data following the SEER multiple tumor guidelines to ensure the definition of multiple primary tumors are the same for ACTUR and SEER patients.

To reduce potential confounding effects from demographic and other variables on the survival, we matched SEER cases to ACTUR cases on age (within 5 years), sex (male and female), race (White, Black, Asian/Pacific islander), and diagnosis year group (1987–1989, 1990–1994, 1995–1999, 2000–2004, 2005–2009, 2010–2012) with a matching ratio of 4:1.

Study Variables

The outcome for this study was all-cause mortality. All-cause mortality was used because the data on cancer-specific mortality from ACTUR were incomplete. In addition to all-cause mortality, we also compared cancer stage at diagnosis and radiation receipt. We defined tumor stages according to American Joint Committee on Cancer’s TNM system (AJCC) criteria[16] including stages I, II, III, and IV. For the earlier years, when the AJCC 6th stages were unavailable in ACTUR, we consolidated the pathologic and clinical T, N, and M stages to the AJCC 6th stages following the AJCC 6th staging rules. Considering clinical application and a larger sample size in each stage, we also used the Veteran Administration Lung Study Group (VALSG) stages, commonly used in clinical practice [17, 18], which defines the tumor stage as “limited stage” or “extensive stage”. The limited-stage corresponds to AJCC stages I to III excluding T3–4 and the extensive-stage corresponds to AJCC stage IV disease or T3–4 with multiple lung nodules.[19] Tumor registries such as SEER and ACTUR use the TNM staging system for SCLC. Tumor grade was defined as well-differentiated (grade I), moderately-differentiated (grade II), poorly differentiated (grade III), non-differentiated (grade IV) using the AJCC’s criteria.[16]

Site-specific cancer-directed surgery codes were used to define cancer-directed surgery types according to SEER guidelines.[20] Radiation treatment, defined as radiation therapy performed as part of the first course of treatment, was grouped into “Radiation therapy administered”, “Radiation therapy not administered”, or “Unknown” according to SEER guidelines.[21]

In addition to the matching variables (age, sex, race, diagnosis year), other demographic variables included in the study were Hispanic ethnicity (Non-Hispanic, Hispanic, or unknown), region of diagnosis (Northeast, South, Midwest, West, and Other, as defined by the U.S. Census Bureau) and age as a continuous variable.

Statistical Analysis

We first compared the distributions of demographic and tumor characteristics between ACTUR and SEER patients using the Chi-square test. In survival analysis, the follow-up time was calculated as the time from diagnosis to death or the end of the study, December 31, 2013. Patients who were not dead (alive or loss to follow up) at the end of the study were censored on the study end date. Kaplan-Meier curves were used to compare survival between patients from ACTUR and SEER overall and by VALSG stage. Multivariable Cox proportional hazards models for matched data were then used to estimate hazard ratios (HRs) and 95% CIs for ACTUR compared with SEER. The proportional hazards assumption was checked by plotting the log-log survival curves.[22] To further control for the effects of potential confounders, we adjusted for the non-matched variables including demographic characteristics (ethnicity, region of diagnosis and continuous age), tumor features (tumor stage, tumor grade), cancer-directed surgery (yes, no, unknown), and radiation treatment (yes, no, unknown ). All Cox models were also stratified by the matching variables to compare survival between the two patient cohorts in demographic subgroups.

For the comparisons of ACTUR and SEER in VALSG tumor stage at diagnosis (extensive stage vs. limited stage) and receipt of radiation therapy, we used multinomial multivariable logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs) adjusted for potential confounding variables. Surgery was not compared between the two populations in multivariable analyses because it is not a main treatment for SCLC and the frequencies of receiving surgery were very low in both populations (Table 1). Nevertheless, it was adjusted for in multivariable analyses because of the significant difference in the frequency between the two populations and its potential effects on survival. Data on chemotherapy were not available in the SEER public-use file and thus comparisons could not be made in chemotherapy receipt.

Table 1.

Demographic and tumor characteristics of SCLC cases diagnosed during 1987–2012 in ACTUR and SEER registries

	ACTUR (N=3040)		SEER (N=12,160)		p-value
	N	%	N	%
Age group					1.00
<50	156	5.13	624	5.13
50–64	1397	45.95	5588	45.95
65–79	1352	44.47	5408	44.47
80 or older	135	4.44	540	4.44
Sex					1.00
Male	1846	60.72	7384	60.72
Female	1194	39.28	4776	39.28
Race					1.00
White	2781	91.48	11124	91.48
Black	184	6.05	736	6.05
Asian or Pacific Islander	75	2.47	300	2.47
Year of diagnosis					1.00
1987–1989	419	13.78	1676	13.78
1990–1994	935	30.76	3740	30.76
1995–1999	662	21.78	2648	21.78
2000–2004	480	15.79	1920	15.79
2005–2009	367	12.07	1468	12.07
2010–2012	177	5.82	708	5.82
Ethnicity
Non-Hispanic	1595	52.47	11664	95.92	<0.001
Hispanic	79	2.60	496	4.08
Unknown	1366	44.93	0	0.00
Region of diagnosis *					<0.001
Northeast	40	1.32	1790	14.72
South	1746	57.43	1844	15.16
Midwest	328	10.79	3218	26.46
West	826	27.17	5308	43.65
Other	100	3.29	0	0.00
Tumor stage					<0.001
Stage I	261	8.59	992	8.16
Stage II	103	3.39	229	1.88
Stage III	678	22.30	3136	25.79
Stage IV	1489	48.98	6211	51.08
Unknown	509	16.74	1592	13.09
Tumor grade					<0.001
Well differentiated, grade1	21	0.69	69	0.57
Moderately differentiated, grade 2	36	1.18	132	1.09
Poorly differentiated, grade 3	368	12.11	1009	8.30
Undifferentiated, grade 4	899	29.57	5138	42.25
Unknown	1716	56.45	5812	47.80
Surgery					<0.001
No	2692	88.55	10744	88.36
Yes	278	9.14	839	6.90
Unknown	70	2.30	577	4.75
Radiation treatment					<0.001
No	1581	52.01	6543	53.81
Yes	1343	44.18	5314	43.70
Unknown	116	3.82	303	2.49

^*Region was derived from state at diagnosis. Specific states in a region follow U.S. Census Bureau definition.

Finally, to assess if survival differences were independent of tumor stage and radiation treatment, the Cox hazard models were stratified by VALSG tumor stage (limited stage, extensive stage, or unknown), and radiation (yes, no, or unknown), respectively.

All statistical analyses were conducted using the SAS software version 9.4.0 (SAS Institute, Inc.). All reported p-values are two sided with the significance level set at p<0.05.

Results

This study included 3,040 ACTUR cases and 12,160 matched SEER cases. The ACTUR and SEER cases had the same distributions in matching variables (age group, sex, race and year of diagnosis) (all p=1.00) (Table 1). There were differences between the two populations in region of diagnosis (p<0.001) and Hispanic ethnicity (p<0.001). There were also significant differences in the distributions of tumor stage (p<0.001) and tumor grade (p<0.001) between the two populations. Specifically, ACTUR cases were more likely to present with stage I (8.59% vs. 8.16%), stage II disease (3.39% vs. 1.88%), or unknown stage (16.74% vs. 13.09%) and less likely to have stage III (22.30% vs. 25.79%) or stage IV disease (48.98% vs. 51.08%) than SEER cases. They were also less likely to have grade IV tumor (29.57% vs. 42.25%) but more likely to have grade III (12.11% vs. 8.30%) or unknown grade (56.45% vs. 47.80%) tumors. ACTUR patients were more likely to receive surgery (9.14% vs. 6.90%). The percentage of radiation receipt was slightly higher in ACTUR than SEER (44.18% vs. 43.70%) and percentage of “unknown” radiation receipt was higher in ACTUR than SEER (3.82% vs. 2.49%).

The median follow-up times for ACTUR and SEER cases were 10 months and 8 months, respectively. The Kaplan-Meier survival analysis showed that ACTUR cases exhibited significantly better overall survival than SEER cases (log-rank p<0.0001) (Figure 1). When stratified by tumor stage, the better survival of ACTUR patients than SEER patients was observed for both limited and extensive stages, respectively (Figure 2). In multivariable Cox model, there was 23% lower mortality among ACTUR cases than SEER cases (HR=0.77, 95% CI=0.71–0.83) (Table 2). In an analysis stratified by the matching variables, the lower mortality in ACTUR than SEER was observed in nearly all subgroups stratified by age group, gender, race (except Asian/Pacific Islander).

Figure 1.

Kaplan-Meier survival curve for ACTUR and SEER patients with SCLC diagnosed during 1987–2012

Figure 2(a).

Kaplan-Meier survival curve for ACTUR and SEER patients with limited stage SCLC diagnosed during 1987–2012

Table 2.

Overall and stratified hazard ratios of all-cause mortality comparing ACTUR with SEER among SCLC diagnosed between 1987 and 2012

Variables	Numbers		Adjusted HRa (95% CI)
	All cases	Deaths
Overall
SEER	12160	11656	1.00 (ref.)
ACTUR	3040	2947	0.77 (0.71–0.83)
By Age
<50
SEER	624	583	1.00 (ref.)
ACTUR	156	140	0.55 (0.37–0.81)
50–64
SEER	5588	5314	1.00 (ref.)
ACTUR	1397	1353	0.72 (0.64–0.80)
65–79
SEER	5408	5235	1.00 (ref.)
ACTUR	1352	1319	0.88 (0.79–0.98)
80 or older
SEER	540	524	1.00 (ref.)
ACTUR	135	135	0.52 (0.37–0.73)
By Gender
Male
SEER	7384	7151	1.00 (ref.)
ACTUR	1846	1804	0.78 (0.71–0.87)
Female
SEER	4776	4505	1.00 (ref.)
ACTUR	1194	1143	0.75 (0.67–0.84)
By Race
White
SEER	11124	10683	1.00 (ref.)
ACTUR	2781	2698	0.76 (0.70–0.82)
Black
SEER	736	717	1.00 (ref.)
ACTUR	184	178	0.70 (0.53–0.92)
Asian/Pacific Islander
SEER	300	256	1.00 (ref.)
ACTUR	75	71	1.34 (0.87–2.07)

^aHRs were estimated from Cox proportional hazard models for matched data further adjusting age as a continuous variable, Hispanic origin, region at diagnosis, tumor stage, tumor grade, surgery and radiation receipt.

HR=Hazard ratio; CI=Confidence Interval

Table 3 shows the comparisons of tumor stage and radiation receipt between the two populations. There was no significant difference in VALSG stage between the two populations (OR=1.05; 95% CI=0.93–1.19). The comparison of radiation treatment receipt showed that ACTUR cases had higher odds of receiving radiation treatment than SEER patients (OR=1.26, 95% CI=1.12–1.42) after adjustment for potential confounders.

Table 3.

Odds ratios of stage at diagnosis and radiation receipt comparing ACTUR with SEER among SCLC cases diagnosed between 1987 and 2012

	ACTUR	SEER	Odds ratio (95% CI) ACTUR vs. SEER
Tumor stage
Limited Stage	1042	4357	Ref.
Extensive Stage	1489	6211	1.05 (0.93–1.19)a
Radiation receipt
No	1581	6543	Ref.
Yes	1343	5314	1.26 (1.12–1.42)b

^aAll ORs were estimated from multivariable logistic regression model. ORs were adjusted for age (as a continuous variable), sex, race, Hispanic origin, year of diagnosis, region of diagnosis and tumor grade.

^bOR was estimated from multivariable logistic regression model adjusted for age (as a continuous variable), race, Hispanic origin, year of diagnosis, region of diagnosis, tumor stage, tumor grade and surgery.

Table 4 shows the differences in survival between the two populations stratified by tumor stage and radiation. The better survival of ACTUR cases was observed for all tumor stages (HR=0.81, 95% =0.71–0.93 for limited stage; HR=0.74, 95% CI=0.67–0.82 for extensive stage). When the analysis was stratified by radiation treatment receipt, better survival in ACTUR than SEER remained significant in both strata (HR=0.84, 95% CI=0.78–0.92 for radiation; HR=0.82, 95% CI=0.75–0.89 for no radiation).

Table 4.

Stratified hazard ratios of all-cause mortality comparing ACTUR with SEER among SCLC patients diagnosed between 1987 and 2012

Variables	Numbers		Adjusted HRa (95% CI)
	All Cases	Deaths
By tumor stage
Limited Stage
SEER	4357	4032	1.00 (ref.)
ACTUR	1042	971	0.81 (0.71–0.93)
Extensive Stage
SEER	6211	6069	1.00 (ref.)
ACTUR	1489	1475	0.74 (0.67–0.82)
Unknown stage
SEER	1592	1555	1.00 (ref.)
ACTUR	509	501	0.80 (0.61–1.08)
By Radiation
Radiation-Yes
SEER	5314	5057	1.00 (ref.)
ACTUR	1343	1292	0.84 (0.78–0.92)
Radiation-No
SEER	6543	6305	1.00 (ref.)
ACTUR	1581	1540	0.82 (0.75–0.89)
Unknown
SEER	303	294	1.00 (ref.)
ACTUR	116	115	0.58 (0.41–0.81)

^aAll HRs were estimated from multivariable Cox proportional hazard model adjusted for age (as continuous variable), sex, race, diagnosis year, Hispanic origin, region of diagnosis, tumor stage, tumor grade, surgery and radiation, except for the stratified variable itself. HR=Hazard ratio; CI=Confidence Interval

Discussion

To the best of our knowledge, our study is the first one comparing survival among SCLC patients between MHS and the U.S. general population. In this study, we found that MHS beneficiaries with SCLC exhibited better overall survival than similar patients from the U.S. general population. The survival advantage was present in patients of all age groups, races, and genders. The 23% reduction in mortality in this study is consistent with our previous study on non-small-cell lung cancer, which showed a significant 22% reduction in mortality in the MHS compared to SEER.[8] The consistent findings of the two studies supports a survival benefit of the universal care system over the general population for lung cancer as a whole.

Access to care or insurance status is associated with survival among cancer patients in the U.S.[1, 23–27] However, most lung cancer studies have been on NSCLC, while studies on SCLC have been limited. In a study of limited-stage SCLC identified from the National Cancer Database, patients without health insurance or with Medicaid had shorter survival compared to those with private or managed care insurance.[5] Two other studies compared survival of SCLC patients between the U.S. general population and patients in the Veterans Health Administration (VHA) health system, a large integrated health care system with improved care access to its beneficiaries.[28, 29] Landrum et al. compared survival of patients 65 or older in the Veteran Health Administration (VHA) and those from SEER-Medicare.[28] The VA patients had both VA and Medicare insurance and therefore may have better access to care. While they reported no significant difference in all-cause mortality among SCLC patients after adjusting for demographic characteristics, comorbidity, tumor stage and tumor size, further propensity score adjustment for performance status and severity of comorbidities showed that VHA patients had better survival than SEER-Medicare patients (HR=0.84, 95% CI=0.79–0.89).[28] However, an alternative study, which compared survival between SCLC cancer patients from VHA Medical Centers in Pennsylvania and those from the Pennsylvania Cancer Registry, reported shorter 5-year age-adjusted survival for patients in the VHA.[29] However, the study did not control for the effects of potential confounding factors other than age, such as tumor stage, which may bias the findings.

SCLC is characterized by rapid growth, early metastatic spread, and poor survival.[17] The better survival that we reported in the current study suggests that the survival benefit of a universal care system extends to highly aggressive tumors, such as SCLC. The MHS is one of the largest health care systems in the United States and provides universal access to health care to its 9.6 million beneficiaries.[7] MHS beneficiaries receive health care free of charge or with minimal out-of-pocket cost,[7] thus financial barriers to health care access are largely reduced. In conjunction with similar findings of our studies on other cancers,[8, 30, 31] this study suggests that the MHS’s universal health care may have translated into the improved survival outcome across various cancer sites.

Tumor stage at diagnosis is a significant predictor of survival in cancer. While MHS beneficiaries with SCLC had better survival than their SEER counterparts, stage at diagnosis was similar between the two populations. Furthermore, in stratified analysis of survival by stage, the survival advantage of MHS beneficiaries (ACTUR patients) remained regardless of cancer stage. This suggests that tumor stage at diagnosis may not be a significant factor in the difference between the two populations in survival. Given that lung cancer screening was not yet standard practice during the time period of our study, future studies are warranted to assess whether the universal care system is beneficial to SCLC early diagnosis.

Thoracic radiation therapy is part of the recommended combination therapies for SCLC patients to improve survival. The higher likelihood of receiving radiation therapy among MHS beneficiaries than SEER counterparts in our study is an indication of higher utilization of cancer treatment services in MHS. In a study comparing treatment between patients age 65 or older in the VHA and the SEER-Medicare population, Keating et al. (2011) reported higher rates of receiving chemotherapy and radiotherapy in patients with limited stage SCLC from VHA, only after propensity score adjustment for severe comorbid illness.[6] In a National Cancer Database study, the odds of receiving radiation therapy and/or chemotherapy for limited stage SCLC were higher among patients with private or managed care insurance than patients without insurance, Medicaid or Medicare alone.[5] The odds of surgical resection for stage I SCLC were significantly lower among persons who were uninsured or had Medicaid than among persons with non-Medicaid insurance in a SEER study.[32] While the studies differed on patient variables, tumor characteristics, and measures of treatment, both results supported an association between better insurance and higher utilization of cancer treatment services. However, the better survival of ACTUR than SEER patients regardless of radiation therapy in the current study suggests that radiation therapy may not significantly contribute to the survival difference. Nevertheless, due to the lack of chemotherapy data in the SEER public-use data, we are unable to assess how differences in chemotherapy, combined therapy, therapy modality, and the timing of the therapies could contribute to the survival difference, as these are important factors to SCLC prognosis.[33–36] Given that chemotherapy is a main treatment for stage IV lung cancer, the lack of chemotherapy data limits the scope of the treatment comparison in the current study. Thus, we were unable to evaluate whether the difference in chemotherapy could contribute to the survival. A more comprehensive analysis is warranted in the future to assess the role of treatment in the identified survival difference.

In addition to treatment, other factors may be associated with survival at the levels of patient, provider, and health care delivery[1, 24, 25, 37–39] . These factors include adherence to screening and treatment guidelines,[25, 37–39] comorbidities, health belief and literacy and social support, [1, 25, 37] overall quality of care received,[24] other health delivery factors (such as variations in health care management),[38] and healthy worker effect. In regard to healthy worker effect, active-duty military personnel are healthier than the general population and thus might have a better survival overall. However, 97% of the ACTUR patients included in the study were non-active duty patients (family members of active duty, retirees and their family members), most of whom are similar to the general population. Future studies are warranted to identify whether these and other factors that might contribute to the improved survival outcome in the MHS.

The current study had some limitations. First, the coverage of the areas in the SEER data increased over time and thus the representativeness of the SEER data for the U.S. population varied by time. Second, due to the features of cancer registry data, data on some potential confounders such as socioeconomic status and comorbidities were not available and thus their influences on the study results could not be evaluated. Third, in addition to the lack of chemotherapy data, radiation therapy data may not completely capture information to accurately distinguish “No” and “Unknown” categories [40], which could lead to misclassifications. Finally, since all-cause mortality rather than cancer-specific death was used as the study outcome, the potential effects on survival from causes other than SCLC could not be excluded. However, this may not be a major concern, given that most patients with SCLC die of the disease.

Conclusions

Our study suggests that universal health care may play an important role to improve survival of patients with highly aggressive SCLC. Future studies are warranted to identify components of the universal health care and other factors that may contribute to the improved survival.

Figure 2(b).

Kaplan-Meier survival curve for ACTUR and SEER patients with extensive stage SCLC diagnosed during 1987–2012

List of Abbreviations and Acronyms

ACTUR

Automated Central Tumor Registry

AJCC

American Joint Committee on Cancer

CI

Confidence Interval

DoD

Department of Defense

HR

Hazard Ratio

ICD-O-3

International Classification of Diseases for Oncology, third edition

MHS

Military Health System

MTFs

Military Treatment Facilities

NAACCR

North American Association of Central Cancer Registries

NCI

National Cancer Institute

NSCLC

Non-Small Cell Lung Cancer

OR

Odds Ratio

SCLC

Small-Cell Lung Cancer

SEER

Surveillance, Epidemiology, and End Results

VALSG

Veteran Administration Lung Study Group

VHA

Veteran Health Administration