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Original Research: Lung Cancer |

Natural History of Typical Pulmonary Carcinoid TumorsNatural History of Pulmonary Carcinoid Tumors: A Comparison of Nonsurgical and Surgical Treatment FREE TO VIEW

Dan J. Raz, MD, MAS; Rebecca A. Nelson, PhD; Frederic W. Grannis, MD; Jae Y. Kim, MD
Author and Funding Information

From the Division of Thoracic Surgery (Drs Raz, Grannis, and Kim) and Department of Biostatistics (Dr Nelson), City of Hope Medical Center, Duarte, CA.

CORRESPONDENCE TO: Dan J. Raz, MD, MAS, Division of Thoracic Surgery, City of Hope Medical Center, 1500 E Duarte Rd, Duarte, CA 91010; e-mail: draz@coh.org


FUNDING/SUPPORT: This work was supported by the National Cancer Institute of the National Institutes of Health [Grant NIH 5K12CA001727-20].

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(4):1111-1117. doi:10.1378/chest.14-1960
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BACKGROUND:  The natural history of typical pulmonary carcinoid tumors has not been described and has important implications for counseling elderly patients or patients with high operative-risk about surgical resection.

METHODS:  Data from the Surveillance, Epidemiology, and End Results Program were used to identify 4,111 patients with biopsy specimen-proven lymph node-negative typical carcinoid tumor of the lung between 1988 and 2010; 306 had no resection, 929 underwent sublobar resection, and 2,876 underwent lobectomy. Overall survival and disease-specific survival (DSS) were analyzed using Kaplan-Meier plots. Multivariate analysis was used to determine predictors of survival.

RESULTS:  Five-year overall survival in patients who underwent lobectomy, sublobar resection, or no surgery was 93%, 92%, and 69%, respectively (P < .0001); 5-year DSS was 97%, 98%, and 88%, respectively (P < .0001). Among T1 tumors, DSS was 98% for patients who underwent lobectomy and sublobar resection and 92% for no surgery; among T2 tumors, DSS was 97%, 100%, and 87%, respectively, and among T3 and T4 tumors, it was 96%, 100%, and 75%, respectively. On multivariate analysis, nonoperative management was associated with an increased risk for disease-specific mortality compared with lobectomy (hazard ratio, 2.14; 95% CI, 1.35-3.40; P = .0013).

CONCLUSIONS:  In this population-based cohort, surgical resection of lymph node-negative carcinoid tumors is associated with a survival advantage over nonoperative treatment. However, the DSS at 5 years was still high without any treatment, suggesting that observation of asymptomatic peripheral typical carcinoid tumors or endoscopic management of symptomatic central carcinoid tumors may be considered in patients at high risk for surgical resection.

Figures in this Article

Little is known about the natural history of pulmonary carcinoid tumors. Pulmonary carcinoid tumors may present as incidental peripheral lung lesions or as symptomatic endobronchial lesions.1 Typical carcinoid tumors, the most common pulmonary carcinoid tumors, are associated with 90% to 95% 5-year overall survival (OS) with surgical resection.1,2 One small patient series reported that the doubling time of pulmonary carcinoid tumors averages 80 months for typical carcinoid tumors.3 As the number of lung nodules detected incidentally on CT screening for lung cancer or other indications increases, it is important to understand the natural history of nonresected typical pulmonary carcinoid tumors. This information can be useful in informing elderly patients, patients with limited life expectancy, or patients at high operative risk about the expected outcomes with nonoperative management of asymptomatic peripheral carcinoid tumors or endobronchial treatment of central tumors. Using data from the Surveillance, Epidemiology, and End Results (SEER) program, we describe the survival of patients with biopsy specimen-proven, lymph node-negative typical carcinoid tumors who did not undergo surgical resection compared with who did.

Patients

Patient data were obtained from the SEER website.4 The SEER catchment area covers approximately 28% of the United States, and the dataset contains clinicopathologic information, treatment specifics, OS, and disease-specific survival (DSS). Disease-specific death codes are used if the index cancer is the patient’s first primary, with “disease specific” defined as death caused by cancer of the same site or cancer of the same body system. In addition, if the patient had only one cancer in his or her lifetime (sequence code = 00), any cause of death by cancer and death due to noncancer diseases related to the site of cancer are considered disease specific. Another cancer or cancers that develop (sequence code = 01) in addition to cancer of the same site and cancer of the same body system, death from cancer attributed to multiple cancers with an unknown primary, and death from noncancer diseases related to the site of first cancer diagnosis are coded as disease specific. Tumor location, grade, and histology were coded according to the International Classification of Diseases for Oncology, Version 3 (ICD-O-3). Tumor stage was coded according to the seventh edition of the American Joint Committee on Cancer TNM staging system.5 SEER requires registries to update disease and vital status on all cases annually. This study was reviewed by our institutional review board and was determined to be exempt research.

Table 1 summarizes the inclusion and exclusion of patients in the study. Included in the analyses were patients aged ≥ 18 years with histologically confirmed nonmetastatic lung cancer (ICD-O-3 site code C34) between January 1988 and December 2010. Only patients classified with typical carcinoid histology (ICD-O-3 morphology code 8240) were included in the study dataset. In addition, patients with lymph node-positive disease or insufficient staging information or who received radiation were excluded. Since 2002, SEER has provided information on whether lymph node status was determined based on clinical stage or pathologic examination of lymph nodes with or without excision of the primary tumor. In 1,796 patients with information on lymph node status, diagnosis in 1,181 (66%) was based on histologic examination of lymph nodes, 41 patients (2%) may have had lymph nodes examined without primary tumor, and diagnosis in 574 (32%) was based on clinical staging alone. Cases where T stage was not coded or unknown (TX) were included in the study but analyzed separately. Patients with a history of cancer were excluded, as were patients receiving a diagnosis at autopsy or while in hospice. Of the 782,468 patients with lung cancer in the SEER registry between 1988 and 2010, the final sample comprised 4,111 patients. Procedure codes available in SEER were then assigned to one of three groups: lobectomy, sublobar resection, and no surgery. Within the lobectomy category, we included sleeve lobectomy, bilobectomy, and pneumonectomy, and within the sublobar resection category, we included bronchial sleeve resection (resection of bronchus alone without lung parenchyma). Among patients coded as having no surgery, we included 51 who had local tumor destruction with laser, cautery/fulguration, or tumor destruction not otherwise specified.

Table Graphic Jump Location
TABLE 1 ]  Stepwise Cohort Selection
Statistical Analysis

Patient demographic and clinical characteristics were compared across treatment groups using the Pearson χ2 test for categorical nominal data and the Jonckheere-Terpstra nonparametric test for categorical ordinal data. As a continuous variable, age was compared across groups using the Student t test. Univariate and multivariate Cox proportional hazard models identified factors associated with improved DSS and OS, with results reported using hazard ratios (HRs) and 95% CIs. In addition, the proportional hazard assumptions for the Cox models were tested by calculating scaled Schoenfeld residuals. Results indicated model fit or flat residuals secondary to large sample sizes.

Kaplan-Meier curves were used to calculate median and 5- and 10-year DSS and OS rates, with the log-rank test used to determine statistical differences across groups. Survival time, in years, was calculated from the date of diagnosis until the date of death. If the patient was alive, he or she was censored at the date of last contact. For the DSS analyses, patients who died of lung cancer (SEER variable dth_class = 1) were identified using cause of death on the death certificate. Patients who died of causes unrelated to their lung cancer were censored at the date of death. Median follow-up time for the 3,494 patients (85%) alive at last contact was 5.8 years (interquartile range, 2.7-10.2 years; mean ± SD, 7.1 ± 5.5 years). All analyses were performed using SAS software (SAS Institute Inc) with two-sided P ≤ .05 considered statistically significant.

OS at 5 years was 93% for lobectomy, 92% for sublobar resection, and 69% without surgery (P < .0001) (Fig 1A). Median survival was not reached for the lobectomy or sublobar resection groups and was 10 years for nonsurgical patients (95% CI, 8-not reached years). DSS at 5 years (Fig 1B) was 97% for lobectomy, 98% for sublobar resection, and 88% without surgery. DSS at 10 years was 95%, 96%, and 85%, respectively (P < .0001, log-rank test). There was no clinically meaningful difference in 10-year DSS among patients undergoing lobectomy with increasing T stage (96% for T1 and 95% for T2, P = .012) or sublobar resection (96% for T1 and 93% for T2, P = .71). However, among patients who did not undergo surgery, DSS at 10 years was 87% for T2 tumors and 92% for T1 tumors, although the difference was not statistically significant (P = .16). We did not include values for T3/T4 tumors because of the small numbers of nonsurgical patients with these tumors. Median DSS time was not reached in the lobectomy, sublobar resection, or nonsurgical groups. Among sublobar resections were 519 wedge resections and 129 segmentectomies; 10-year DSS was 96% for both categories (P = .56).

Figure Jump LinkFigure 1 –  A, B, Overall (A) and disease-specific (B) survival in patients with lymph node-negative typical pulmonary carcinoid tumors undergoing lobectomy, sublobar resection, or no surgery.Grahic Jump Location

Patient characteristics stratified by lobectomy, sublobar resection, or nonsurgical treatment are summarized in Table 2. Nonsurgical patients were older; in fact, 23.2% of these patients were aged ≥ 80 years compared with 5.9% of the patients undergoing sublobar resection and 2.6% undergoing lobectomy (P < .0001). Black patients underwent surgery less often than nonblack patients (P = .006) and presented with higher T stages than nonblack patients (P = .0027). Patients who did not undergo surgical lung resection had a higher proportion of tumors within the mainstem bronchus (13.4% vs 4.3% for lobectomy, P < .001); however, due to limitations with the coding system, it is unclear how many patients with nonmainstem locations actually had centrally located vs peripheral tumors. Patients undergoing sublobar resection were more likely to have T1 disease than those undergoing lobectomy or nonsurgical treatment (79%, 65%, and 36%, respectively; P < .001), although a large proportion of nonsurgical patients had tumors coded as TX (35%). Not surprisingly, fewer lymph nodes were examined among patients undergoing sublobar resection or no surgery (82% and 94%, respectively, had 0-4 lymph nodes examined vs 35% of patients undergoing lobectomy; P < .001). At least nine patients (3%) who did not undergo surgery had lymph nodes sampled by mediastinoscopy, endobronchial ultrasound, or other methods.

Table Graphic Jump Location
TABLE 2 ]  Patient, Tumor, and Treatment-Related Characteristics in Patients Stratified by Treatment Status

Data are presented as median (interquartile range), No. (%), or mean ± SD. P values for follow-up time reflect nonparametric testing using the Kruskal-Wallis test. NOS = not otherwise specified.

a 

P values shown are based on the Jonckheere-Terpstra test for ordinal data. All other P values are based on χ2 test across groups.

On multivariate analysis, nonsurgical patients were more than twice as likely to die than patients who underwent lobectomy (OS HR, 2.23; 95% CI, 1.67-2.96; P < .0001) after controlling for age, sex, race/ethnicity, and T stage. Based on DSS data, the risk of dying from disease was also twice as likely in nonsurgical patients than in patients who underwent lobectomy (HR, 2.14; 95% CI, 1.35-3.40; P = .001). Increasing age was associated with disease-specific mortality, with patients aged ≥ 80 years having an HR of 14.10 (95% CI, 6.53-29.10; P < .001) compared with patients aged 18 to 49 years.

Blacks had a higher rate of disease-specific mortality (HR, 2.13; 95% CI, 1.26-3.59; P = .005) than whites on multivariate analysis. Comparing various clinical variables, blacks were less likely to undergo surgery than whites (no surgery, 14% vs 7%, respectively; P = .0004) and were less likely to have T1 disease (56% vs 67%, respectively; P = .0054). Among the 306 patients who did not undergo a resection, 156 (51%) were not recommended surgery, 51 (17%) underwent bronchoscopic management instead of resection (reasons not given), 18 (6%) refused recommended surgery, 13 (4%) had conditions that contraindicated surgery, and 68 (22%) had unknown or other reasons for not undergoing resection. Table 3 lists the reasons for not undergoing resection stratified by age category.

Table Graphic Jump Location
TABLE 3 ]  Reasons for No Surgery, Stratified by Age Group

Data are presented as No. (%).

a 

Minor surgical procedures included local tumor destruction, laser excision, and cryosurgery.

In this population-based cohort, surgical resection of typical carcinoid tumors is associated with greater OS and DSS than nonsurgical treatment in patients with lymph node-negative biopsy specimens. Patients undergoing lobectomy, sublobar resection, and no surgery had different clinical characteristics, which may influence survival. Specifically, patients who did not undergo surgical resection were older. In addition, patients who underwent sublobar resection were more likely to have T1 disease than those undergoing lobectomy or no surgery. These and other unmeasured variables may have led to decreased survival rates in patients undergoing nonoperative treatment. Despite this, the DSS at 10 years is still high without resection. Specifically, we found that 10-year DSS was 85% for those undergoing nonsurgical treatment compared with 95% for those undergoing lobectomy.

Patients who underwent no surgery were more likely to have mainstem bronchus involvement than those who underwent surgery. It is possible that the presence of main bronchial involvement was a reason for nonoperative treatment because resection would have involved a more complex procedure than that for a peripheral carcinoid tumor. We did not identify any significant survival difference between patients with a mainstem vs a nonmainstem location undergoing nonsurgical treatment. However, aside from mainstem location, SEER does not provide data on whether a tumor was peripheral or central, which limits the interpretation of data on tumor location and outcome.

The present findings are consistent with a report from our institution describing an average doubling time of close to 7 years for typical carcinoid tumors.3 The present results are also consistent with series reporting no difference in outcomes between sublobar resection and lobectomy for typical carcinoid tumors.6,7 The OS and DSS rates described herein are in line with other series of treated pulmonary carcinoid tumor, which show very few cases of disease recurrence among patients with typical carcinoid tumors.1,2

We also observed that black race and older age were associated with a higher rate of disease-specific mortality on multivariate analysis. These findings have not been reported elsewhere to our knowledge, and the reasons for these findings are unclear. Erroneous attribution of cause of death to carcinoid tumor is possible, which would account for an increased disease-specific mortality with increasing age. Blacks with carcinoid tumors were less likely than whites to undergo surgery and had a more advanced T stage, two variables that were associated with increased mortality. However, these variables should have been controlled for in multivariate analysis. It is unclear whether higher disease-specific mortality in blacks in multivariate modeling is a result of incompletely controlled confounding variables, such as socioeconomic status or access to care, or whether the biology of carcinoid tumors in blacks is more aggressive. This possible disparity should be addressed with further research. Consistent with prior reports, we also found that the proportion of women with typical carcinoid tumors was double that of men, but sex did not seem to have an effect on prognosis.8

The present findings have important implications for counseling patients with incidentally detected carcinoid tumors. Patients who can tolerate surgical resection seem to have a survival benefit compared with no treatment, although the magnitude of that difference is unclear due to selection bias. However, patients with limited life expectancy or those at high risk for surgery may have excellent survival long term without surgical resection. Unfortunately, the data do not provide any insight into the degree to which symptoms may develop over time or into the quality of life of patients who choose not to undergo resection. It is possible that respiratory symptoms develop with time in patients who do not undergo resection of peripheral carcinoid tumors, and this should be factored into the decision-making regarding continued expectant management. Although the data do not have the granularity to address this specific question, patients with endobronchial tumors who are not fit for thoracotomy and surgical resection may be considered for palliation with endobronchial tumor resection. Stereotactic body radiation therapy is another option for treatment of small peripheral lung tumors, although there are few data on its efficacy in pulmonary carcinoid tumors.

This study has several limitations. Patients who did not undergo surgical resection were older and more likely to have comorbidities that precluded surgical resection than patients who underwent surgical resection. We did not have sufficient data on comorbidities to analyze the effect of this variable on survival in this study cohort. Nonetheless, we had data on DSS and reasons for not undergoing surgical resection. DSS may overestimate true DSS in an indolent disease such as carcinoid tumor in patients with competing risk factors for death. In other words, because patients in this population are much more likely to die of a disease other than their carcinoid tumor, it is difficult to estimate a precise DSS. Therefore, the present estimate of DSS should be interpreted with caution, especially when counseling patients with a life expectancy of at least 5 to 10 years. Moreover, patients who did not undergo surgical resection were unlikely to have mediastinal or hilar lymph nodes sampled and, therefore, may have had occult nodal metastases, leading to understaging. This would have resulted in worse-than-expected DSS among nonsurgical patients and would not have altered the conclusion that survival without surgical resection is still high. The lack of nodal sampling in nonsurgical patients may lead to an underestimation of the true long-term survival. In addition, biopsy specimens from nonsurgical patients were likely to be small in the amount of material for examination, which may have resulted in misclassification of tumor type.9,10 In this study, we only included patients given a histologic diagnosis based on, for example, endobronchial forceps biopsy or core needle biopsy and excluded patients given a diagnosis based on cytology or unspecified methods to minimize the possibility of tumor misclassification. Finally, these data came from SEER, a cancer registry database. There are limitations of using SEER, such as a lack of individual case review and variability in treatment patterns. Although a prospective study of expectant management of asymptomatic typical carcinoid tumors would be ideal, such a study is unlikely to ever be organized.

To our knowledge, this study is the largest of untreated lung carcinoid tumors reported to date. It provides important information for counseling patients with asymptomatic typical carcinoid tumors of the lung regarding the outcome with and without surgical resection. We emphasize that patients who are fit for surgery should still undergo resection. Although there was selection bias in the assignment of treatment in this study, the data demonstrate a survival benefit to resection on multivariate analysis. Moreover, the mortality of lobectomy in high-volume centers is approximately 1%, whereas the mortality of sleeve lobectomy and sleeve resection is only about 2%.11,12 In patients with limited life expectancy who are symptomatic, these data may be useful regarding palliation of endobronchial lesions with endobronchial therapies. Although surgical resection is probably associated with improved survival, survival without resection is still excellent.

Author contributions: D. J. R. had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. D. J. R., R. A. N., F. W. G., and J. Y. K. contributed to the study design; D. J. R. and R. A. N. contributed to the data analysis and interpretation and writing of the manuscript; and F. W. G. and J. Y. K. contributed to editing the manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Role of sponsors: The content is solely the responsibility of Dr Raz and does not necessarily represent the official views of the National Institutes of Health.

Other contributions: Research was performed at City of Hope Medical Center, Duarte, CA.

DSS

disease-specific survival

HR

hazard ratio

ICD-O-3

International Classification of Diseases for Oncology, Version 3

OS

overall survival

SEER

Surveillance, Epidemiology, and End Results

Detterbeck FC. Management of carcinoid tumors. Ann Thorac Surg. 2010;89(3):998-1005. [CrossRef] [PubMed]
 
Lou F, Sarkaria I, Pietanza C, et al. Recurrence of pulmonary carcinoid tumors after resection: implications for postoperative surveillance. Ann Thorac Surg. 2013;96(4):1156-1162. [CrossRef] [PubMed]
 
DeCaro LF, Paladugu R, Benfield JR, Lovisatti L, Pak H, Teplitz RL. Typical and atypical carcinoids within the pulmonary APUD tumor spectrum. J Thorac Cardiovasc Surg. 1983;86(4):528-536. [PubMed]
 
Surveillance, Epidemiology, and End Results (SEER) research data (1973-2010). National Cancer Institute SEER website. http://www.seer.cancer.gov. Accessed April 1, 2014.
 
Edge S, Byrd DR, Compton CC, Fritz AG, Greene FL, Trotti A., eds. AJCC Cancer Staging Manual.7th ed. New York, NY: Springer; 2010.
 
Fox M, Van Berkel V, Bousamra M II, Sloan S, Martin RC II. Surgical management of pulmonary carcinoid tumors: sublobar resection versus lobectomy. Am J Surg. 2013;205(2):200-208. [CrossRef] [PubMed]
 
Yendamuri S, Gold D, Jayaprakash V, Dexter E, Nwogu C, Demmy T. Is sublobar resection sufficient for carcinoid tumors? Ann Thorac Surg. 2011;92(5):1774-1778. [CrossRef] [PubMed]
 
Modlin IM, Lye KD, Kidd M. A 5-decade analysis of 13,715 carcinoid tumors. Cancer. 2003;97(4):934-959. [CrossRef] [PubMed]
 
Frierson HF Jr, Covell JL, Mills SE. Fine needle aspiration cytology of atypical carcinoid of the lung. Acta Cytol. 1987;31(4):471-475. [PubMed]
 
Szyfelbein WM, Ross JS. Carcinoids, atypical carcinoids, and small-cell carcinomas of the lung: differential diagnosis of fine-needle aspiration biopsy specimens. Diagn Cytopathol. 1988;4(1):1-8. [CrossRef] [PubMed]
 
Merritt RE, Mathisen DJ, Wain JC, et al. Long-term results of sleeve lobectomy in the management of non-small cell lung carcinoma and low-grade neoplasms. Ann Thorac Surg. 2009;88(5):1574-1581. [CrossRef] [PubMed]
 
Paul S, Altorki NK, Sheng S, et al. Thoracoscopic lobectomy is associated with lower morbidity than open lobectomy: a propensity-matched analysis from the STS database. J Thorac Cardiovasc Surg. 2010;139(2):366-378. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1 –  A, B, Overall (A) and disease-specific (B) survival in patients with lymph node-negative typical pulmonary carcinoid tumors undergoing lobectomy, sublobar resection, or no surgery.Grahic Jump Location

Tables

Table Graphic Jump Location
TABLE 1 ]  Stepwise Cohort Selection
Table Graphic Jump Location
TABLE 2 ]  Patient, Tumor, and Treatment-Related Characteristics in Patients Stratified by Treatment Status

Data are presented as median (interquartile range), No. (%), or mean ± SD. P values for follow-up time reflect nonparametric testing using the Kruskal-Wallis test. NOS = not otherwise specified.

a 

P values shown are based on the Jonckheere-Terpstra test for ordinal data. All other P values are based on χ2 test across groups.

Table Graphic Jump Location
TABLE 3 ]  Reasons for No Surgery, Stratified by Age Group

Data are presented as No. (%).

a 

Minor surgical procedures included local tumor destruction, laser excision, and cryosurgery.

References

Detterbeck FC. Management of carcinoid tumors. Ann Thorac Surg. 2010;89(3):998-1005. [CrossRef] [PubMed]
 
Lou F, Sarkaria I, Pietanza C, et al. Recurrence of pulmonary carcinoid tumors after resection: implications for postoperative surveillance. Ann Thorac Surg. 2013;96(4):1156-1162. [CrossRef] [PubMed]
 
DeCaro LF, Paladugu R, Benfield JR, Lovisatti L, Pak H, Teplitz RL. Typical and atypical carcinoids within the pulmonary APUD tumor spectrum. J Thorac Cardiovasc Surg. 1983;86(4):528-536. [PubMed]
 
Surveillance, Epidemiology, and End Results (SEER) research data (1973-2010). National Cancer Institute SEER website. http://www.seer.cancer.gov. Accessed April 1, 2014.
 
Edge S, Byrd DR, Compton CC, Fritz AG, Greene FL, Trotti A., eds. AJCC Cancer Staging Manual.7th ed. New York, NY: Springer; 2010.
 
Fox M, Van Berkel V, Bousamra M II, Sloan S, Martin RC II. Surgical management of pulmonary carcinoid tumors: sublobar resection versus lobectomy. Am J Surg. 2013;205(2):200-208. [CrossRef] [PubMed]
 
Yendamuri S, Gold D, Jayaprakash V, Dexter E, Nwogu C, Demmy T. Is sublobar resection sufficient for carcinoid tumors? Ann Thorac Surg. 2011;92(5):1774-1778. [CrossRef] [PubMed]
 
Modlin IM, Lye KD, Kidd M. A 5-decade analysis of 13,715 carcinoid tumors. Cancer. 2003;97(4):934-959. [CrossRef] [PubMed]
 
Frierson HF Jr, Covell JL, Mills SE. Fine needle aspiration cytology of atypical carcinoid of the lung. Acta Cytol. 1987;31(4):471-475. [PubMed]
 
Szyfelbein WM, Ross JS. Carcinoids, atypical carcinoids, and small-cell carcinomas of the lung: differential diagnosis of fine-needle aspiration biopsy specimens. Diagn Cytopathol. 1988;4(1):1-8. [CrossRef] [PubMed]
 
Merritt RE, Mathisen DJ, Wain JC, et al. Long-term results of sleeve lobectomy in the management of non-small cell lung carcinoma and low-grade neoplasms. Ann Thorac Surg. 2009;88(5):1574-1581. [CrossRef] [PubMed]
 
Paul S, Altorki NK, Sheng S, et al. Thoracoscopic lobectomy is associated with lower morbidity than open lobectomy: a propensity-matched analysis from the STS database. J Thorac Cardiovasc Surg. 2010;139(2):366-378. [CrossRef] [PubMed]
 
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