Rare airway tumors: an update on current diagnostic and management strategies

Introduction

Primary tracheobronchial neoplasms represent approximately 0.1% of all pulmonary tumors (1). They have been a topic of interest for many decades due to the challenge in their diagnosis and management. Many of tracheobronchial tumors are found incidentally. They are sometimes misdiagnosed as asthma or chronic obstructive pulmonary disease. The past few decades have seen an increase in the diagnosis of these tumors due to the rising popularity of flexible bronchoscopy and advancement in related techniques. We present a review of rare airway tumors (RATs) that have been presented in the literature as case reports or case series and discuss pertinent aspects of the different airway tumors with focus on epidemiology, pathology and genetics, clinical presentation, diagnosis, treatment and outcomes. The Cochrane Library and Medline from 1990 to 2015 was searched to identify the rare airway tumors and to provide a comprehensive review for tumors of the tracheobronchial tree that are considered rare. Following search terms were used: rare airway tumor, tracheal tumors, and rare bronchial tumors. We have focused on rare neoplasms based on incidence and atypical presentation that arise in the tracheobronchial tree from the subglottic to the segmental bronchioles. These tumors were classified based on cell type as well as metastatic potential (Table 1) (1).

Table 1 List of rare airway tumors classified based on cell type and malignant potential
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Epidemiology

It is difficult to determine the actual prevalence, geographical distribution, gender predominance, age predominance and associated risk factors of these rare tumors (1-4). Furthermore, there is no epidemiological data due to the lack of large prospective or retrospective clinical studies. Through individual review of most up-to-date case reports and reviews of each individual tumor, we present the prevalence of each tumor as percentage of primary pulmonary tumors (1-15) or as number of reported cases as well as gender predominance, age predominance and associated risk factors, Table 2 (16-28).

Table 2 Epidemiological criteria of rare airway tumors including prevalence, gender predominance, age predominance and associated risk factors
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Pathology, genetics and immunohistochemistry

There have been very limited reports on the genetics, pathology and associations of RATs. Some of that information has been an extrapolation based on known pathogenesis of these tumors that occurs in other organs. In this paper, we discuss available information on some of the unique genetic and pathological criteria as well as the associations of some of these rare tracheobronchial tumors.

Pulmonary salivary gland-type tumors account for <1% of pulmonary tumors but are distinct group (29). Mucoepidermoid carcinoma (MEC) is the most common type (Figure 1) followed by adenoid cystic carcinoma (ACC) (29). These tumors are indistinguishable histologically from their salivary gland counterparts. They originate from the submucosal glands of the tracheobronchial tree and have structural homology to the exocrine glands. They can be distinguished by cell type as MEC is composed of mucoid and epidermoid cells that are squamous cells while ACC is composed of cribriform, tubular, or solid growth patterns with monomorphic tumor cells. A recent review on the salivary gland tumor reports the difference in term of immunohistochemistry (IHC) and molecular features between these tumors (30). Pulmonary MEC was reported to have positive immune sensitivity for p63, p40, cytokeratin (CK)7 and CK5/6 and negative IHC for CK20, thyroid transcription factor-1 (TTF-1), and napsin A (6,31). This immunohistochemical distinction is important because adenocarcinoma and adenosquamous carcinoma of the lung are difficult to differentiate from MEC by cytomorphology. On the other hand, ACC was determined to be immunoreactive to pan Cytokeratin, CD117 and proto-oncogene MYB (30). In term of molecular features, around 40% to 75% of MEC of the head and neck region have shown a characteristic association with translocation, t(11;19)(q21;p13). In one study 24 cases of pulmonary MEC showed a mastermind-like 2 (MAML2) on chromosome 11q21 rearrangement by fluorescence in situ hybridization thus demonstrating an importance of this test in diagnostic work up (31). Recent review also showed that around 50% of studied ACC demonstrate tumor-specific t(6;9)(q22-23;p23-24) translocation generating a MYB (v-myb avian viral oncogene homolog) proto-oncogene fusion with the transcription factor gene NFIB (nuclear factor IB) (30).

Figure 1 Mucoepidermoid carcinoma. (A) axial chest CT image showing the complete obstruction of the left main stem bronchus. The obstructive lesion is highly vascularized with a bronchial artery branch originating from the descending aorta (arrow); (B) chest CT three-dimensional reconstruction showing the complete obstruction of the left main stem (arrow); (C) bronchoscopic image showing the complete obstruction of the left main stem by a large tumor (arrow); (D) microscopic image of biopsy showing mucoepidermoid carcinoma. The image shows neoplastic tissue composed of round to oval epithelioid cells and occasional goblet cells (red arrow) punctuated by mucin containing cystic spaces (yellow arrow). Hematoxylin and Eosin stain (200×); (E) microscopic image showing mucicarmine staining of mucoepidermoid carcinoma. The image shows intracellular (blue arrow) and extracellular mucin (yellow arrow). Mucicarmine stain (200×).

Another interesting rare malignant airway tumor is the epithelial-myopeithelial carcinoma. P53 gene and adenomatous polyposis coli (APC) gene has been implicated in the pathogenesis of epithelial-myoepithelial carcinoma (32-34). Although involvement was shown in a case report, more information is needed to show direct association. The immunohistochemical stain for Ki-67 (a cellular marker for proliferation) revealed increased mitotic activity (32).

Papilloma is another unusual tumor due to its various cell types and association with human papilloma virus (HPV) (Figure 2). Papilloma is classified into 3 categories: squamous, glandular and mixed. Squamous cell papillomas have been associated with tobacco smoking as well as HPV (8). A study by Inamura et al. reported 78% of HPV identification in squamous papilloma while none in mixed and glandular cases suggesting that sub types of papilloma’s differ in etiology (8). Katial et al. found HPV DNA in squamous papilloma (reference). The study by Shibuya et al. and Lang et al. showed that HPV serotype 6 and 11 is the most common type associated with papilloma with low risk of malignant transformation (35,36). Go et al. showed that p53 status is not a molecular marker for malignant transformation in papillomas and its expression is variable (37).

Figure 2 Endobronchial papilloma. (A) bronchoscopic view showing a small a polypoid endobronchial lesion (arrow) in the lateral wall of the bronchus intermedius; (B) ablation using argon plasma coagulation of the endobronchial lesion in the bronchus intermedius; (C) a six-month follow up showing endobronchial minimal scaring and no evidence of recurrence; (D) microscopic image of a papilloma. The image shows tissue fragments composed of fibrovascular core lined by benign squamous epithelium. Hematoxylin and Eosin stain (100×).

The World Health Organization (WHO) have classified neuroendocrine tumors of the lung into three main entities: carcinoid tumors (typical/atypical), large cell neuroendocrine carcinomas (LCNEC), and small cell carcinomas (SCC) (9). Classification of typical and atypical carcinoid tumors, LCNEC and SCC are based on the histologic appearance, and presence of necrosis and mitoses (9). This review focused on typical carcinoid (TC) and atypical carcinoid (AC) tumors. The WHO diagnostic criteria for TC are: a tumor with neuroendocrine morphology and <2 mitoses/2 mm² (10 high power fileds (HPF), lacking necrosis and tumor 0.5 cm or larger. AC are tumors with neuroendocrine morphology with 2 to 10 mitoses/2 mm² and/or necrosis (often punctate). About 75–90% of bronchopulmonary carcinoids are centrally located while only 10–25% are peripheral. TCs represent 90% of pulmonary carcinoid tumors. They tend to occur in younger patients and metastasize to lymph node in 5–15% and to distant sites in 3% at the time of presentation (38). On the contrary, AC are rare (0.1–0.2%) lung tumors; however, metastasis to lymph node (40–50%) or distant sites (20%) are common at presentation. Furthermore, neuroendocrine tumors have also been associated with multiple endocrine neoplasia type I (MEN1), an autosomal dominant disorder associated with the gene locus on 11q13. In one series around 5% of patient with MEN1 were associated with pulmonary carcinoid, while higher incidence of 31% was reported in another study (39). Inactivation of the MEN1 gene by mutation is evident in TC (47%), AC (70%), LCNEC (52%), and SCLC (41%) (40-42). Onuki et al. noted that 11q13 gene mutation was more common in LCNEC (71%) and SCLC (67%). Abnormal expression or loss of heterogenosity and point mutations of the p53 locus have been detected less commonly in TC (4%) than AC (29%) (43,44). Expression of p53 protein in AC is correlated with a higher apoptotic index. An older study reports 10q and 13q sequences and allow further cytogenetic differences between AC and TC (45).

Leiomyoma is a benign tumor, which arises from smooth muscle fibers surrounding the airway or in the blood vessels. Multiple cases of leiomyoma have been reported in patients with HIV/AIDS and cellular immunity deficiency (46). Along with HIV virus, leiomyoma have been reported in immunocompromised patients with Epstein-Barr Virus (EBV) infection. The exact pathophysiology is not yet clear and many cases of leiomyoma have been reported in immunocompetent patients suggesting the possibility of multiple etiologies (47,48).

Inflammatory myofibroblastic tumors (IMT) are distinctive tumors composed of myofibroblastic spindle cell population as well as inflammatory infiltrate of plasma cells, lymphocytes and eosinophils. The etiology for this tumor is not well understood but many believe it is initiated due to an inflammatory process like trauma or surgery and even infection (49). One study suggests COX2 and VEGF, as mediators of angiogenesis, which may play a role in the pathogenesis and growth of IMT (50). In the past couple of years, IMT have got recognition as true tumors than inflammatory process due to reported cases showing presence of clonal chromosomal abnormalities of 2p23 and rearrangement of the anaplastic lymphoma kinase (ALK) receptor tyrosine-kinase gene locus or fusion of ALK with the clathrin heavy chain gene localized on 17q23 (51,52).

Diagnosis

Clinical presentation

Many of the RATs are diagnosed incidentally on computed tomogram (CT) imaging or bronchoscopy. Although they tend to have similar clinical presentation and course, RATs may present with different degree of symptomatic severity, depending on the location, size, degree of obstruction, growth rate, and other characteristics of these neoplasms (3-26). However, when symptomatic, they all share common constellation of signs and symptoms attributed to tracheobronchial obstruction (Figure 3). Most RATs present with cough and dyspnea, and sometimes with hemoptysis, wheezing and stridor. Other less common symptoms include pleuritic chest pain, hoarseness and dysphagia (1). Associated signs include hypoxia, wheezing and stridor. In some cases, RATs may be misdiagnosed as asthma or chronic obstructive pulmonary disease especially when the onset of symptoms is gradual.

Figure 3 Endobronchial lipoma. (A) axial chest CT showing an endobronchial abnormality in the superior segment of the right lower lobe; (B) bronchoscopic image of the large endobronchial soft polypoid lesion originating from the superior segment of the right lower lobe; (C) microscopic image of an airway lipoma. The image shows airway epithelium on the right lower corner and submucosal tissue replaced by benign adipocytes. Hematoxylin and Eosin stain (200×).

Diagnostic radiology and bronchoscopy

Conventional chest radiographs are not usually diagnostic, yet are commonly obtained as the initial radiological test. Chest CT is the most useful radiologic method to assess the airway tumors and to delineate the extraluminal extent of the tumor (5). MRI provides no clear advantage over CT in the assessment of airway tumors, except for those with salivary gland-type tumors (53). In those cases, MRI T1-weighted imaging provides better visualization of the glands hyper-intense fatty tissue and delineates the border of the tumor. Pulmonary function testing can be sometimes helpful if there is presence of obstructive pattern or abnormal flow-volume loops that have characteristic flattening as seen in dynamic extrathoracic/intrathoracic obstruction or fixed airway obstruction (1). Bronchoscopy is the diagnostic modality of choice for airway tumors as it allows for direct visualization for localization, tissue sampling and staging (5,54) The extent of the airway tumor and its relation to the surrounding structure can be evaluated using the radial probe endobronchial ultrasound (RP-EBUS) (55,56). Besides, the curvilinear EBUS can be used to evaluate the mediastinal lymph nodes for metastasis (57).

The diagnostic approach for most the rare airway tumors discussed in this review follow the above approach (1-15). There are subtle differences in the diagnostic work-up for these tumors depending on the extent of the disease. General summary of the diagnostic tool and associated findings of each tumor is presented below (Table 3) (16-26,30-33,36,38,48,58,59) .

Table 3 Radiological, endoscopic and histochemical diagnostic findings of rare airway tumors based on literature reports
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Treatment

The treatment of airway tumors requires a multi-disciplinary approach. The interventional pulmonologist, surgeon, anesthesiologist and pathologist all play a crucial role in the management of these tumors. While the treatment of these tumors is complex, good short and long-term outcomes that are possible with a well-planned and well-executed treatment paradigm justify the effort involved.

The first step in the treatment includes a diagnostic biopsy. Easy as that seems, bronchoscopic biopsy requires astute clinical judgment and comfort level and experience with rigid bronchoscopy and multiple hemostatic techniques utilized to control airway hemorrhage that may ensue from a biopsy. The goals of bronchoscopy are:

• To assess the precise location and extent of the disease along with the depth of invasion: this may require the use of regular adult bronchoscopes along with low profile, ultra-slim bronchoscopes to bypass the tumor and assess the distal airway. Assessment of a patent distal airway confers a certain degree of safety should an endoscopic destruction be considered. It also provides invaluable guidance for surgical planning, something a virtual bronchoscopy may not be able to provide;
• To obtain a histologic diagnosis: the histology of the disease process guides treatment. Most pathology identified in the Table 1 is curable with complete resection. However, some pathology may be better dealt with by chemotherapy or radiation. For example, it is only in the rare situation that resection, surgical or endoscopic would be recommended for metastatic melanoma of the airway. The need for a histologic diagnosis must be balanced against the risk of bleeding. For example, if a lesion looks like a classic carcinoid in an eminently resectable location in a fit patient, it may be entirely reasonable to go for surgery without histologic diagnosis. However, as a general rule, it is useful to have histology before treatment. The risk of bleeding can be often assessed by pre-operative scanning with IV contrast (useful for identifying hemangiomas) or with the use of curvilinear or radial endobronchial ultrasound;
• To render a blocked airway patent: there are two situations in which this becomes particularly important. First, in the case of a patient with metastatic disease where the stage of the disease precludes curative resection, a palliative endobronchial destruction to improve the quality of life is the optimal course. Second, in the case of a patient with a completely obstructing endobronchial tumor with distal collapse or infection, opening up the airway helps with assessment of resectability as well as to obtain time to optimize the patient for surgery. In addition, this may be necessary for anesthetic management. The classic example of this situation is a carinal tumor that near-obstructs the left mainstem bronchus. As the surgical approach would be through a right thoracotomy, intubation of the left mainstem to obtain lung isolation is critical. In this situation, the optimal approach would be to open up the left mainstem with multimodality bronchoscopic techniques, place an endotracheal tube in the left mainstem bronchus to obtain good lung isolation and then approach the resection via right thoracotomy.

Bronchoscopic destruction of endobronchial tumors can be accomplished in several ways. These include electrocautery, cryotherapy, argon plasma coagulation (APC), and laser (light amplification by stimulated emission of radiation) using Neodymium-Yttrium-Aluminum-Garnet (Nd:YAG), Neodymium-Yttrium-Aluminum-Perovskite (Nd:YAP), carbon dioxide lasers and others (60). Electrocautery involves tissue destruction using an electric current. It is best suited for small intraluminal tumors in early stages with curative intent (61). It has risk of intraluminal bleeding and perforation. APC, on the other hand, is a mode of noncontact electro-coagulation that involves forming plasma at the tip of a probe which produces coagulative necrosis in the targeted tissue (61). APC is useful in targeting lesions at sharp angles and provides excellent hemostasis. Laser therapy is useful for tumor debulking and among other used laser types, Nd:YAG is the most commonly used (61). Nd:YAG Laser has an invisible beam with wavelength that lies in the infrared region with depth up to 10 mm (compared to 1–5 mm for APC). With the exception of the carbon dioxide laser that requires rigid bronchoscopy, most other laser types can be used through the flexible bronchoscope. In contrast, cryotherapy relies on the repeated freeze-thaw cycles using extremely cold temperatures to destroy tumor tissue (61). Cryotherapy results in both physical and vascular damage of the tumor. It has very low risk of bleeding and perforation. Airway dilation using sequential balloon or rigid bronchoscopy techniques is another approach that is usually used in combination with other bronchoscopic modalities or as a palliative measure to maintain airway patency (61).

The factors that impact the successful bronchoscopic intervention are the extension of the tumor to the distally beyond the central airways, complex tumors with wider mucosal extension (more than three bronchial rings), bronchial wall invasion toward other mediastinal structures, and determining cartilage invasion with radial probe EBUS (54). Endoscopic approach is preferred over surgical approach in patients with multiple co-morbidities and high surgical risk. Other treatment such as chemotherapy, radiotherapy and anti-inflammatory drugs may be used in conjunction with surgical or endoscopic management or as palliation for patient who have tumors that are candidates for endoscopic or surgical management (3,4,6,7,9,13-23). A summary of most employed treatment modalities for rare airway tumors is provided in Table 4 (26,32,36,47,49,58-60,62-67).

Table 4 Treatment modalities for rare airway tumors
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Surgical treatment is aimed at obtaining negative surgical margins while sparing as much lung parenchyma as possible. In tumors distal to the carina, sleeve resection is preferred over pneumonectomy whenever feasible. In lesions at or proximal to the carina, often, complete sparing of all lung parenchyma is possible. While it is beyond the scope of this article to discuss the details of all possible combinations of resection, it is important to note that the resections should be carefully planned by an experienced team that includes the interventional pulmonologist, surgeon and anesthesiologist. All patients should be planned on being extubated on the table. The interventional pulmonologist’s involvement continues into the post-operative period in order to handle post-resection stenosis, even though this should be rare (<5%).

Outcomes

The overall survival of rare airway tumors depends on multiple factors including tumor malignant potential, patient’s co-morbidities, location, and risks of treatment modality. Benign tumors are usually localized and amendable to resection with no or minimal risk of recurrence (1). Benign tumors are usually treated with surgical resection with very low recurrence rate. Tumors that are treated with endoscopic excision have varying degrees of recurrence, but re-excision is usually feasible (1,54,62). Imaging and bronchoscopy are usually used to survey for possible recurrence (5,54). The outcome of malignant tumors is variable and depends on location, lymph node involvement and mediastinal invasion of vital organs (1,26).

Acknowledgements

None.

Footnote

Conflicts of Interest: KH is a consultant for cook medical. The other authors have no conflicts of interest to declare.

References

1. Macchiarini P. Primary tracheal tumours. Lancet Oncol 2006;7:83-91. [Crossref] [PubMed]
2. Kim TS, Lee KS, Han J, et al. Sialadenoid tumors of the respiratory tract: radiologic-pathologic correlation. AJR Am J Roentgenol 2001;177:1145-50. [Crossref] [PubMed]
3. Hsu AA, Tan EH, Takano AM. Lower Respiratory Tract Adenoid Cystic Carcinoma: Its Management in the Past Decades. Clin Oncol (R Coll Radiol) 2015;27:732-40. [Crossref] [PubMed]
4. Hu MM, Hu Y, He JB, et al. Primary adenoid cystic carcinoma of the lung: Clinicopathological features, treatment and results. Oncol Lett 2015;9:1475-81. [PubMed]
5. Park CM, Goo JM, Lee HJ, et al. Tumors in the tracheobronchial tree: CT and FDG PET features. Radiographics 2009;29:55-71. [Crossref] [PubMed]
6. Liu X, Adams AL. Mucoepidermoid carcinoma of the bronchus: a review. Arch Pathol Lab Med 2007;131:1400-4. [PubMed]
7. Paganin F, Prevot M, Noel JB, et al. A solitary bronchial papilloma with unusual endoscopic presentation: case study and literature review. BMC Pulm Med 2009;9:40. [Crossref] [PubMed]
8. Inamura K, Kumasaka T, Furuta R, et al. Mixed squamous cell and glandular papilloma of the lung: a case study and literature review. Pathol Int 2011;61:252-8. [Crossref] [PubMed]
9. Hadda V, Madan K, Mohan A, et al. Successful flexible bronchoscopic management of dynamic central airway obstruction by a large tracheal carcinoid tumor. Case Rep Pulmonol 2014;2014:349707.
10. Park JS, Lee M, Kim HK, et al. Primary leiomyoma of the trachea, bronchus, and pulmonary parenchyma--a single-institutional experience. Eur J Cardiothorac Surg 2012;41:41-5. [Crossref] [PubMed]
11. Swarnakar R, Sinha S. Endobronchial leiomyoma: A rare and innocent tumour of the bronchial tree. Lung India 2013;30:57-60. [Crossref] [PubMed]
12. Dumoulin E, Gui X, Stather DR, et al. Endobronchial schwannoma. J Bronchology Interv Pulmonol 2012;19:75-7. [Crossref] [PubMed]
13. Sim JK, Choi JH, Oh JY, et al. Two Cases of Diagnosis and Removal of Endobronchial Hamartoma by Cryotherapy via Flexible Bronchoscopy. Tuberc Respir Dis (Seoul) 2014;76:141-5. [Crossref] [PubMed]
14. Jennings S, Tharion J, Jones P, et al. Bronchial haemangioma: exceptionally rare cause of haemoptysis. Heart Lung Circ 2013;22:1030-2. [Crossref] [PubMed]
15. Triviño A, Mora-Cabezas M, Vallejo-Benitez A, et al. Endobronchial lipoma: a rare cause of bronchial occlusion. Arch Bronconeumol 2013;49:494-6. [Article in English, Spanish]. [Crossref] [PubMed]
16. Fernandez-Bussy S, Labarca G, Descalzi F, et al. Endobronchial chondromas. Respir Care 2014;59:e193-6. [Crossref] [PubMed]
17. Choi IH, Song DH, Kim J, et al. Two cases of glomus tumor arising in large airway: well organized radiologic, macroscopic and microscopic findings. Tuberc Respir Dis (Seoul) 2014;76:34-7. [Crossref] [PubMed]
18. Sakr L, Palaniappan R, Payan MJ, et al. Tracheal glomus tumor: a multidisciplinary approach to management. Respir Care 2011;56:342-6. [Crossref] [PubMed]
19. Jivan V, Litwin D, Kaini N. Submucosal Granular Cell Tumor-A Rare Case Of Lower Airway Involvement. Am J Respir Crit Care Med. 2013;187:A6136.
20. Matsumoto S, Fujimoto N, Fuchimoto Y, et al. Endobronchial T-cell lymphoma in a patient with chronic pyothorax. Respirol Case Rep 2015;3:44-7. [Crossref] [PubMed]
21. Ding J, Chen Z, Shi M. Tracheal stenting for primary tracheal mucosa-associated lymphoid tissue lymphoma. Eur J Med Res 2013;18:8. [Crossref] [PubMed]
22. Solomonov A, Zuckerman T, Goralnik L, et al. Non-Hodgkin's lymphoma presenting as an endobronchial tumor: report of eight cases and literature review. Am J Hematol 2008;83:416-9. [Crossref] [PubMed]
23. Gladish GW, Sabloff BM, Munden RF, et al. Primary thoracic sarcomas. Radiographics 2002;22:621-37. [Crossref] [PubMed]
24. Massey C, Laver N, Bedi H, et al. Primary fibrosarcoma of the trachea presenting with acute airway loss. Am J Otolaryngol 2015;36:287-9. [Crossref] [PubMed]
25. Özgül MA, Toru Ü, Acat M, et al. A rare tumor of trachea: Inflammatory myofibroblastic tumor diagnosis and endoscopic treatment. Respir Med Case Rep 2014;13:57-60. [PubMed]
26. Woo Park C, Kim W, Jae Oh I, et al. Solitary extramedullary plasmacytoma presenting as an endobronchial mass. Intern Med 2013;52:2113-6. [Crossref] [PubMed]
27. Yang FF, Gao R, Miao Y, et al. Primary tracheobronchial non-Hodgkin lymphoma causing life-threatening airway obstruction: a case report. J Thorac Dis 2015;7:E667-71. [PubMed]
28. Joung MK, Lee YJ, Chung CU, et al. A case of granular cell tumor of the trachea. Korean J Intern Med 2007;22:101-5. [Crossref] [PubMed]
29. Molina JR, Aubry MC, Lewis JE, et al. Primary salivary gland-type lung cancer: spectrum of clinical presentation, histopathologic and prognostic factors. Cancer 2007;110:2253-9. [Crossref] [PubMed]
30. Falk N, Weissferdt A, Kalhor N, et al. Primary Pulmonary Salivary Gland-type Tumors: A Review and Update. Adv Anat Pathol 2016;23:13-23. [Crossref] [PubMed]
31. Roden AC, Garcia JJ, Wehrs RN, et al. Histopathologic, immunophenotypic and cytogenetic features of pulmonary mucoepidermoid carcinoma. Mod Pathol 2014;27:1479-88. [Crossref] [PubMed]
32. Ru K, Srivastava A, Tischler AS. Bronchial epithelial-myoepithelial carcinoma. Arch Pathol Lab Med 2004;128:92-4. [PubMed]
33. Daa T, Kashima K, Gamachi A, et al. Epithelial-myoepithelial carcinoma harboring p53 mutation. APMIS 2001;109:316-20. [Crossref] [PubMed]
34. Young J, Barker M, Robertson T, et al. A case of myoepithelial carcinoma displaying biallelic inactivation of the tumour suppressor gene APC in a patient with familial adenomatous polyposis. J Clin Pathol 2002;55:230-1. [Crossref] [PubMed]
35. Shibuya H, Kutomi T, Kujime K, et al. An adult case of multiple squamous papillomas of the trachea associated with human papilloma virus type 6. Intern Med 2008;47:1535-8. [Crossref] [PubMed]
36. Lang TU, Khalbuss WE, Monaco SE, et al. Solitary Tracheobronchial Papilloma: Cytomorphology and ancillary studies with histologic correlation. Cytojournal 2011;8:6. [Crossref] [PubMed]
37. Go C, Schwartz MR, Donovan DT. Molecular transformation of recurrent respiratory papillomatosis: viral typing and p53 overexpression. Ann Otol Rhinol Laryngol 2003;112:298-302. [Crossref] [PubMed]
38. Davila DG, Dunn WF, Tazelaar HD, et al. Bronchial carcinoid tumors. Mayo Clin Proc 1993;68:795-803. [Crossref] [PubMed]
39. Sachithanandan N, Harle RA, Burgess JR. Bronchopulmonary carcinoid in multiple endocrine neoplasia type 1. Cancer 2005;103:509-15. [Crossref] [PubMed]
40. Zhao J, de Krijger RR, Meier D, et al. Genomic alterations in well-differentiated gastrointestinal and bronchial neuroendocrine tumors (carcinoids): marked differences indicating diversity in molecular pathogenesis. Am J Pathol 2000;157:1431-8. [Crossref] [PubMed]
41. Debelenko LV, Swalwell JI, Kelley MJ, et al. MEN1 gene mutation analysis of high-grade neuroendocrine lung carcinoma. Genes Chromosomes Cancer 2000;28:58-65. [Crossref] [PubMed]
42. Debelenko LV, Brambilla E, Agarwal SK, et al. Identification of MEN1 gene mutations in sporadic carcinoid tumors of the lung. Hum Mol Genet 1997;6:2285-90. [Crossref] [PubMed]
43. Onuki N, Wistuba II, Travis WD, et al. Genetic changes in the spectrum of neuroendocrine lung tumors. Cancer 1999;85:600-7. [Crossref] [PubMed]
44. Gustafsson BI, Kidd M, Chan A, et al. Bronchopulmonary neuroendocrine tumors. Cancer 2008;113:5-21. [Crossref] [PubMed]
45. Laitinen KL, Soini Y, Mattila J, et al. Atypical bronchopulmonary carcinoids show a tendency toward increased apoptotic and proliferative activity. Cancer 2000;88:1590-8. [Crossref] [PubMed]
46. Metta H, Corti M, Redini L, et al. Endobronchial leiomyoma: an unusual non-defining neoplasm in a patient with AIDS. Rev Inst Med Trop Sao Paulo 2009;51:53-5. [Crossref] [PubMed]
47. Cárdenas-García J, Lee-Chang A, Chung V, et al. Bronchial leiomyoma, a case report and review of literature. Respir Med Case Rep 2014;12:59-62. [PubMed]
48. Kwon YS, Kim H, Koh WJ, et al. Clinical characteristics and efficacy of bronchoscopic intervention for tracheobronchial leiomyoma. Respirology 2008;13:908-12. [Crossref] [PubMed]
49. Matsubara O, Tan-Liu NS, Kenney RM, et al. Inflammatory pseudotumors of the lung: progression from organizing pneumonia to fibrous histiocytoma or to plasma cell granuloma in 32 cases. Hum Pathol 1988;19:807-14. [Crossref] [PubMed]
50. Applebaum H, Kieran MW, Cripe TP, et al. The rationale for nonsteroidal anti-inflammatory drug therapy for inflammatory myofibroblastic tumors: a Children's Oncology Group study. J Pediatr Surg 2005;40:999-1003; discussion 1003. [Crossref] [PubMed]
51. Snyder CS, Dell'Aquila M, Haghighi P, et al. Clonal changes in inflammatory pseudotumor of the lung: a case report. Cancer 1995;76:1545-9. [Crossref] [PubMed]
52. Bridge JA, Kanamori M, Ma Z, et al. Fusion of the ALK gene to the clathrin heavy chain gene, CLTC, in inflammatory myofibroblastic tumor. Am J Pathol 2001;159:411-5. [Crossref] [PubMed]
53. Yousem DM, Kraut MA, Chalian AA. Major salivary gland imaging. Radiology 2000;216:19-29. [Crossref] [PubMed]
54. Gao H, Ding X, Wei D, Cheng P, Su X, Liu H, et al. Endoscopic management of benign tracheobronchial tumors. J Thorac Dis 2011;3:255-61. [PubMed]
55. Lund ME, Garland R, Ernst A. Airway stenting: Applications and practice management considerations. Chest 2007;131:579-87. [Crossref] [PubMed]
56. Haas AR, Vachani A, Sterman DH. Advances in diagnostic bronchoscopy. Am J Respir Crit Care Med 2010;182:589-97. [Crossref] [PubMed]
57. Varela-Lema L, Fernandez-Villar A, Ruano-Ravina A. Effectiveness and safety of endobronchial ultrasound-transbronchial needle aspiration: a systematic review. Eur Respir J 2009;33:1156-64. [Crossref] [PubMed]
58. Umezu H, Tamura M, Kobayashi S, Sawabata N, Honma K, Miyoshi S. Tracheal chondrosarcoma. Gen Thorac Cardiovasc Surg 2008;56:199-202. [Crossref] [PubMed]
59. Pecoraro Y, Diso D, Anile M, Russo E, Patella M, Venuta F. Primary inflammatory myofibroblastic tumor of the trachea. Respirol Case Rep 2014;2:147-9. [Crossref] [PubMed]
60. Kim TS, Lee KS, Han J, Im JG, Seo JB, Kim JS, et al. Mucoepidermoid carcinoma of the tracheobronchial tree: radiographic and CT findings in 12 patients. Radiology 1999;212:643-8. [Crossref] [PubMed]
61. Ernst A, Feller-Kopman D, Becker HD, Mehta AC. Central airway obstruction. Am J Respir Crit Care Med 2004;169:1278-97. [Crossref] [PubMed]
62. Wang H, Zhang J, Zhang N, Li D, Zou H, Zhou Y, et al. Bronchoscopic intervention as a main treatment for tracheobronchial adenoid cystic carcinoma. Minim Invasive Ther Allied Technol 2015;24:167-74. [Crossref] [PubMed]
63. Attakkil A, Thorawade V, Jagade M, et al. Tracheal Leiomyoma: A Rare Entity & Role of Diode Laser in Its Management. IJOHNS 2014;3:143-8. [Crossref]
64. Murata T, Shino M, Yasuoka Y, Chikamatsu K. Subglottic Schwannoma: a report of a rare case that was treated with medial thyrotomy. Am J Otolaryngol 2013;34:569-73. [Crossref] [PubMed]
65. Ge X, Han F, Guan W, Sun J, Guo X. Optimal treatment for primary benign intratracheal schwannoma: A case report and review of the literature. Oncol Lett 2015;10:2273-6. [PubMed]
66. Wu HH, Jao YT, Wu MH. Glomus tumor of the trachea managed by spiral tracheoplasty. Am J Case Rep 2014;15:459-65. [Crossref] [PubMed]
67. Ghani S, Desai A, Pokharel S, Demmy T, Dy GK. Pneumonectomy-Sparing NSAID Therapy for Pulmonary Inflammatory Myofibroblastic Tumor. J Thorac Oncol 2015;10:e89-90. [Crossref] [PubMed]