Lung tumors with neuroendocrine morphology: essential radiologic and pathologic features.
* Context.--Tumors with neuroendocrine morphology are a distinct
subset of lung neoplasms sharing characteristic histologic,
immunohistochemical, ultrastructural, and molecular features.
Objective.--To review the current histologic classification and the diagnostic criteria for the major categories of neuroendocrine tumors of the lung.
Data Sources.--Published classification systems from the World Health Organization and pertinent peer-reviewed articles indexed in PubMed (National Library of Medicine) form the basis of this review.
Conclusions.--Accurate classification of the neuroendocrine tumors of the lung requires knowledge of specific criteria separating the major categories, which is essential for determining prognosis and treatment.
Franks, Teri J.
Galvin, Jeffrey R.
|Publication:||Name: Archives of Pathology & Laboratory Medicine Publisher: College of American Pathologists Audience: Academic; Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2008 College of American Pathologists ISSN: 1543-2165|
|Issue:||Date: July, 2008 Source Volume: 132 Source Issue: 7|
|Topic:||Canadian Subject Form: Tumours|
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Tumors with neuroendocrine morphology are a distinct subset of lung
neoplasms that share specific morphologic, immunohistochemical,
ultrastructural, and molecular characteristics. The major categories of
morphologically identifiable neuroendocrine tumors include typical
carcinoid (TC), atypical carcinoid (AC), large cell neuroendocrine
carcinoma (LCNEC), and small cell carcinoma of the lung (SCLC) (Table
1). Although these tumors share a variety of characteristics, widely
varying prognosis and response to therapy necessitated placement in
separate categories within the World Health Organization classification.
(1,2) However, it is easiest to conceptualize this group as a spectrum
of malignancy ranging from low-grade TC, to intermediate-grade AC, to
the 2 high-grade malignancies, LCNEC and SCLC. These 4 carcinomas are
distinguished from nonneuroendocrine lung carcinomas on light microscopy
by their display of neuroendocrine morphology including organoid
nesting, rosette formation, peripheral palisading of tumor nests, and
trabeculae and on immunohistochemistry by reactivity with neuroendocrine
markers. Separation within the neuroendocrine tumors rests primarily on
mitotic rate and the presence or absence of necrosis, and, in the case
of separating LCNEC from SCLC, cell morphology (Table 2).
Although the neuroendocrine tumors of the lung are separated into 4 categories and form a spectrum of malignancy, TC and AC as a group share interesting contrasts to LCNEC and SCLC. Typical carcinoid and AC occur in a younger patient population than LCNEC and SCLC; essentially all patients with LCNEC and SCLC are smokers, whereas approximately one third of TCs and ACs occur in nonsmokers; in contrast to LCNEC and SCLC, TC and AC are frequently associated with neuroendocrine cell hyperplasia with or without tumorlets; and other major histologic subtypes of lung carcinoma occur in combination with LCNEC and SCLC but not with TC and AC. (1) Genetic abnormalities in p53, (3,4) cyclin D1, (5) Bcl-2/Bax, (6) and RB loss and loss of heterozygosity at 3p, (7,8) occur in a higher percentage of LCNECs and SCLCs than TCs and ACs further distinguishing the 2 high-grade malignancies from the 2 carcinoids.
Staging, treatment, and survival vary widely among the 4 neuroendocrine lung tumors, thus accurate histologic classification is essential. The TNM classification is the most widely used staging system for TC, AC, and LCNEC; however, it is generally not applied to SCLC as it is a poor indicator of survival. Instead, SCLC is staged as limited or extensive disease (Table 3). There is essentially equal distribution of limited and extensive disease at diagnosis. (9) Typical carcinoid and AC are treated surgically, most often by lobectomy or pneumonectomy depending on location of the tumor. Whether surgery and/or chemotherapy is the optimal treatment for LCNEC is controversial and has yet to be established. Chemotherapy remains the primary treatment for SCLC. The overall 5-year survival rates for TC, AC, LCNEC, and SCLC after stratification for stage are approximately 90%, 60%, 20%, and 3.5% respectively. (9-11)
TYPICAL AND ATYPICAL CARCINOID
Carcinoids comprise 1% to 2% of all lung neoplasms and are the most common lung tumor of childhood. (12) In large studies, men and women are affected equally, with a mean age of approximately 45 years. (13-15) Symptoms vary with location. Central lesions produce early symptoms including cough, wheezing, dyspnea, and hemoptysis because of airway obstruction, whereas peripheral lesions are frequently discovered incidentally on chest imaging studies in asymptomatic patients. (16,17)
Grossly, carcinoids are well-demarcated masses with tan-yellow or red cut surfaces depending on the extent of vascularity. Necrosis and hemorrhage may be present in AC. Size varies from 0.5 cm to 10 cm, with mean diameters of central lesions greater than those in the periphery and AC greater than TC. (21) Central lesions tend to have a large endobronchial component, but varying extension outside the bronchial wall can result in the bulk of tumor residing in the surrounding lung parenchyma (Figure 2).
Histologically, carcinoids are composed of uniform polygonal, spindle cells, and/or oxyphilic cells with moderate amounts of cytoplasm, fine nuclear chromatin, and inconspicuous nucleoli. Carcinoids are typically histologically heterogeneous displaying a spectrum of growth patterns. Organoid, rosette, palisading, and trabecular patterns of growth are common, but papillary, sclerosing, follicular, or glandular patterns also occur (Figure 3). Mitotic rate and presence or absence of necrosis distinguish TC from AC; TC has fewer than 2 mitoses per 2 [mm.sup.2] (10 high-power fields) without necrosis, whereas AC has 2 to 10 mitoses per 2 [mm.sup.2] (10 high-power fields) and/or necrosis. Pleomorphism and nuclear atypia can be prominent but are unreliable features for separating the 2 carcinoids. (11) The majority of carcinoids are immunoreactive with pancytokeratin, and neuroendocrine differentiation can be confirmed with the neuroendocrine markers chromogranin, synaptophysin, and CD56 (N-CAM).
There are several pitfalls in this setting. Size alone distinguishes tumorlets from the carcinoids, the former are arbitrarily defined as less than 0.5 cm and the latter 0.5 cm or greater, so that on limited material this distinction cannot necessarily be made. On small specimens, such as transbronchial or endobronchial biopsies or needle biopsies, separation of TC from AC is possible if necrosis or a sufficient number of mitoses are present; however, a resected specimen is typically required to make this determination. Because carcinoids often present a significant endobronchial component, surface erosions are common and the endobronchial portion is readily accessible to the bronchoscopists' forceps and needles. Care must be taken not to misinterpret necrosis from erosion and biopsy sites as tumor necrosis; if present, necrosis changes the diagnosis of TC to AC and a worse prognosis. Necrosis in AC is described as punctate, usually occurring in the center of tumor nests (Figure 4), rather than diffuse along the surface as in erosion or linear from instrumentation. Because the nuclear morphology of carcinoid is similar to small cell carcinoma--fine chromatin with inconspicuous nucleoli--care must also be taken in small biopsies to evaluate the volume of cytoplasm and number of mitoses to avoid misdiagnosis. Even in small biopsies, the scant volume of cytoplasm and high mitotic rate of small cell carcinoma are usually evident.
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LARGE CELL NEUROENDOCRINE CARCINOMA
Large cell neuroendocrine carcinoma accounts for approximately 3% of lung cancers, (22) and patients are typically male cigarette smokers in the sixth decade of life. (23) Symptoms produced by the primary tumor are similar to other non-small cell lung carcinomas and vary with location.
The radiologic findings in LCNEC are also indistinguishable from those of other non-small cell lung carcinomas. Approximately 80% of LCNECs appear as peripheral nodules or masses; the remainder form central masses frequently contiguous with the mediastinum. (24,25) Tumors are well-defined and lobulated with an increasingly heterogeneous pattern of enhancement in larger examples (Figure 5).
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Large cell neuroendocrine carcinoma is similar to other non-small cell carcinomas on gross examination. Histologically, LCNEC is composed of cytologically malignant large cells demonstrating neuroendocrine morphology, most commonly rosette formation and peripheral palisading of tumor nests. However, these features are often subtle, making distinction from non-small cell lung carcinoma difficult. In some cases, rosettes are the only histologic marker of neuroendocrine differentiation. Tumor cells show cytologic features of non-small cell lung carcinoma including large cell size, low nuclear-cytoplasmic ratio, vesicular or fine chromatin, and frequent nucleoli. Large cell neuroendocrine carcinoma may have fine nuclear chromatin and lack nucleoli but qualify because of large cell size and abundant cytoplasm. (1) Mitotic counts are defined as greater than 10/2 [mm.sup.2] (10 high-power fields); however, the median count is 70/2 [mm.sup.2]. (1) Necrosis is usually present, often in large zones. Cell size, cytoplasmic volume, and presence of nucleoli facilitate separation from SCLC (Figure 6). The histologic diagnosis of LCNEC requires fulfillment of 2 criteria: demonstration of neuroendocrine morphology by light microscopy and positive immunohistochemical staining for 1 or more neuroendocrine markers (other than neuron-specific enolase). (1,2) Chromogranin, synaptophysin, and CD56 (N-CAM) are the most sensitive and specific neuroendocrine markers. One positive marker is sufficient for diagnosis if the staining is clear cut (2); however, most often several markers will be reactive.
Ten percent to 20% of non-small cell lung cancers (squamous cell, adenocarcinoma, and large cell carcinoma) demonstrate neuroendocrine differentiation by immunohistochemistry but not morphologically and should be classified by conventional subtype with neuroendocrine differentiation noted. (1) Whether these tumors have better or worse survival or are more or less responsive to chemotherapy than non-small cell lung cancers without neuroendocrine differentiation is controversial; studies report better, worse, and no difference in prognosis and response to chemotherapy. (2)
SMALL CELL CARCINOMA
Approximately 20% of lung cancers are SCLCs. (26) Similar to LCNEC, most patients with SCLC are older male smokers. The central location of most tumors gives rise to the common clinical manifestations of cough, dyspnea, and hemoptysis. Invasion of mediastinal structures may result in dysphagia, hoarseness, and superior vena cava syndrome.
Small cell carcinoma is relatively distinctive on imaging. Approximately 95% of tumors are central and related to proximal airways, particularly lobar and main bronchi; less than 5% arise in the peripheral lung without obvious airway association. (27) Central tumors are poorly demarcated. Metastases to hilar lymph nodes and mediastinal involvement secondary to metastases to mediastinal lymph nodes and/or direct invasion from a contiguous mass are almost invariably present (Figure 7). Peripheral SCLC is radiologically indistinguishable from other lung neoplasms.
Grossly, SCLC characteristically spreads along airway submucosa and peribronchovascular connective tissue. Subsequent extension into the lung parenchyma results in an expanding mass that obliterates airways and vessels by external compression rather than intraluminal growth. In contrast to squamous cell carcinoma, endobronchial growth is uncommon in SCLC.
Histologically, SCLCs are composed of small cells, defined as less than the size of three small resting lymphocytes, with scant cytoplasm, fine nuclear chromatin, and inconspicuous or absent nucleoli. (1) Although SCLC can display organoid nesting, rosettes, peripheral palisading of tumor nests, and trabeculae, sheetlike growth with rosettes or absent neuroendocrine morphology are more common. Cell borders are indistinct, spindle morphology may be striking, and molding of tumor cells may be present. The mitotic rate is high with a median of 80/2 [mm.sup.2]. (1) Good quality hematoxylin-eosin-stained sections are essential for evaluation. In suboptimal histologic sections, bubble artifact gives cell nuclei the appearance of having vesicular chromatin, which can lead to an erroneous diagnosis of non-small cell carcinoma (Figure 8).
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Small cell carcinoma is immunoreactive with pancyto-keratin, cytokeratin 7, chromogranin, synaptophysin, CD56, and thyroid transcription factor 1 in most cases; however, up to 10% of tumors are negative for all neuro-endocrine markers. (28) In small biopsies, especially those with extensive crush artifact, separation of SCLC from lymphoma on hematoxylin-eosin staining alone can be difficult; pancytokeratin and/or CD45RB (leukocyte common antigen) stains will usually resolve the problem. Merkel cell carcinoma, in cervical lymph node biopsies, and primitive neuroectodermal tumors are also pitfalls in diagnosis because of their histologic similarity to SCLC. In contrast to SCLC, Merkel cell carcinoma is cytokeratin 20 positive, and cytokeratin 7 and thyroid transcription factor 1 negative, whereas primitive neuroectodermal tumor is CD99 positive, is less mitotically active, and the majority are pancytokeratin negative.
In conclusion, the identification of neuroendocrine tumors of the lung is a step-wise process. First, tumors must be recognized as neuroendocrine by the presence on light microscopy of neuroendocrine morphology including organoid nesting, rosette formation, peripheral palisading of tumor nests, and trabeculae. Once a tumor is considered to be neuroendocrine, separation into the 4 major neuro-endocrine categories is achieved using mitotic rate and the presence or absence of necrosis, and in the instance of separating LCNEC from SCLC, cell morphology. The diagnosis of LCNEC requires the presence of both neuroendocrine morphology by light microscopy and demonstration of neuroendocrine differentiation by immunohistochemistry. Tumors of the lung with neuroendocrine differentiation have widely varying prognosis and response to therapy; thus, accurate histologic classification is essential.
(1.) Travis WD, Colby TV, Corrin B, Shimosato Y, Brambilla E. Histological Typing of Lung and Pleural Tumours. 3rd ed. Berlin, Germany: Springer-Verlag; 1999. World Health Organization International Histological Classification of Tumours.
(2.) Travis WD, Brambilla E, Muller-Hermelink HK, Harris CC, eds. Pathology and Genetics of Tumours of the Lung, Pleura, Thymus and Heart. Lyon, France: IARC Press; 2004. World Health Organization Classification of Tumours.
(3.) Onuki N, Wistuba II, Travis WD, et al. Genetic changes in the spectrum of neuroendocrine lung tumors. Cancer. 1999;85:600-607.
(4.) Przygodzki RM, Finkelstein SD, Langer JC, et al. Analysis of p53, K-ras-2, and C-raf-1 in pulmonary neuroendocrine tumors: correlation with histological subtype and clinical outcome. Am J Pathol. 1996;148:1531-1541.
(5.) Gugger M, Burckhardt E, Kappeler A, Hirsiger H, Laissue JA, Mazzucchelli L. Quantitative expansion of structural genomic alterations in the spectrum of neuroendocrine lung carcinomas. J Pathol. 2002;196:408-415.
(6.) Brambilla E, Negoescu A, Gazzeri S, et al. Apoptosis-related factors p53, Bcl2, and Bax in neuroendocrine lung tumors. Am J Pathol. 1996;149:1941-1952.
(7.) Gouyer V, Gazzeri S, Brambilla E, et al. Loss of heterozygosity at the RB locus correlates with loss of RB protein in primary malignant neuro-endocrine lung carcinomas. Int J Cancer. 1994;58:818-824.
(8.) Gouyer V, Gazzeri S, Bolon I, Drevet C, Brambilla C, Brambilla E. Mechanism of retinoblastoma gene inactivation in the spectrum of neuroendocrine lung tumors. Am J Respir Cell Mol Biol. 1998;18:188-196.
(9.) Lassen U, Osterlind K, Hansen M, Dombernowsky P, Bergman B, Hansen HH. Long-term survival in small-cell lung cancer: posttreatment characteristics in patients surviving 5 to 18+ years--an analysis of 1,714 consecutive patients. J Clin Oncol. 1995;13:1215-1220.
(10.) Paci M, Cavazza A, Annessi V, et al. Large cell neuroendocrine carcinoma of the lung: a 10-year clinicopathologic retrospective study. Ann Thorac Surg. 2004;77:1163-1167.
(11.) Travis WD, Rush W, Flieder DB, et al. Survival analysis of 200 pulmonary neuroendocrine tumors with clarification of criteria for atypical carcinoid and its separation from typical carcinoid. Am J Surg Pathol. 1998;22:934-944.
(12.) Wang LT, Wilkins EW Jr, Bode HH. Bronchial carcinoid tumors in pediatric patients. Chest. 1993;103:1426-1428.
(13.) Godwin JD. Carcinoid tumors: an analysis of 2,837 cases. Cancer. 1975; 36:560-569.
(14.) Ducrocq X, Thomas P, Massard G, et al. Operative risk and prognostic factors of typical bronchial carcinoid tumors. Ann Thorac Surg. 1998;65:1410 1414.
(15.) Schreurs AJ, Westermann CJ, van den Bosch JM, Vanderschueren RG, Brutel de la Riviere A, Knaepen PJ. A twenty-five-year follow-up of ninety-three resected typical carcinoid tumors of the lung. J Thorac Cardiovasc Surg. 1992;104: 1470-1475.
(16.) Fink G, Krelbaum T, Yellin A, et al. Pulmonary carcinoid: presentation, diagnosis, and outcome in 142 cases in Israel and review of 640 cases from the literature. Chest. 2001;119:1647-1651.
(17.) Todd TR, Cooper JD, Weissberg D, Delarue NC, Pearson FG. Bronchial carcinoid tumors: twenty years' experience. J Thorac Cardiovasc Surg. 1980;79: 532-536.
(18.) Okike N, Bernatz PE, Woolner LB. Carcinoid tumors of the lung. Ann Thorac Surg. 1976;22:270-277.
(19.) Beasley MB, Thunnissen FB, Brambilla E, et al. Pulmonary atypical carcinoid: predictors of survival in 106 cases. Hum Pathol. 2000;31:1255-1265.
(20.) Chong S, Lee KS, Chung MJ, Han J, Kwon OJ, Kim TS. Neuroendocrine tumors of the lung: clinical, pathologic, and imaging findings. Radiographics. 2006;26:41-57.
(21.) McCaughan BC, Martini N, Bains MS. Bronchial carcinoids: review of 124 cases. J Thorac Cardiovasc Surg. 1985;89:8-17.
(22.) Takei H, Asamura H, Maeshima A, et al. Large cell neuroendocrine carcinoma of the lung: a clinicopathologic study of eighty-seven cases. J Thorac Cardiovasc Surg. 2002;124:285-292.
(23.) Iyoda A, Hiroshima K, Toyozaki T, Haga Y, Fujisawa T, Ohwada H. Clinical characterization of pulmonary large cell neuroendocrine carcinoma and large cell carcinoma with neuroendocrine morphology. Cancer. 2001;91:1992-2000.
(24.) Jung KJ, Lee KS, Han J, et al. Large cell neuroendocrine carcinoma of the lung: clinical, CT, and pathologic findings in 11 patients. J Thorac Imaging. 2001; 16:156-162.
(25.) Oshiro Y, Kusumoto M, Matsuno Y, et al. CT findings of surgically resected large cell neuroendocrine carcinoma of the lung in 38 patients. AJR Am J Roentgenol. 2004;182:87-91.
(26.) Quinn D, Gianlupi A, Broste S. The changing radiographic presentation of bronchogenic carcinoma with reference to cell types. Chest. 1996;110:1474 1479.
(27.) Fraser RS, Muller NL, Colman N, Pare PD. Fraser and Pare's Diagnosis of Diseases of the Chest. 4th ed. Philadelphia, Pa: WB Saunders; 1999.
(28.) Guinee DG Jr, Fishback NF, Koss MN, Abbondanzo SL, Travis WD. The spectrum of immunohistochemical staining of small-cell lung carcinoma in specimens from transbronchial and open-lung biopsies. Am J Clin Pathol. 1994;102: 406-414.
Accepted for publication December 17, 2007.
Teri J. Franks, MD; Jeffrey R. Galvin, MD
From the Departments of Pulmonary and Mediastinal Pathology (Dr Franks) and Radiologic Pathology (Dr Galvin), Armed Forces Institute of Pathology, Washington, DC; and the Departments of Diagnostic Radiology and Internal Medicine, Division of Pulmonary/Critical Care Medicine, University of Maryland School of Medicine, Baltimore (Dr Galvin).
The authors have no relevant financial interest in the products or companies described in this article.
The opinions and assertions contained herein are the expressed views of the authors and are not to be construed as official or reflecting the views of the Departments of the Army or Defense. This is a US Government work, and as such, is in the public domain in the United States of America.
Reprints: Teri J. Franks, MD, Department of Pulmonary and Mediastinal Pathology, Armed Forces Institute of Pathology, 6825 16th St NW, Bldg 54, Room 2071, Washington, DC 20306 (e-mail: firstname.lastname@example.org).
Table 1. Spectrum of Neuroendocrine Proliferations and Neoplasms of the Lung * Neuroendocrine cell hyperplasia and tumorlets Neuroendocrine cell hyperplasia associated with fibrosis and/or inflammation adjacent to carcinoid tumors diffuse idiopathic neuroendocrine cell hyperplasia with or without airway fibrosis/obstruction Tumorlets Tumors with neuroendocrine morphology Typical carcinoid Atypical carcinoid Large cell neuroendocrine carcinoma Small cell carcinoma Non-small cell carcinomas with neuroendocrine differentiation Other tumors with neuroendocrine properties Pulmonary blastoma Primitive neuroectodermal tumor Desmoplastic round cell tumor Carcinomas with rhabdoid phenotype Paraganglioma * Reprinted from Travis et al,1 with permission from the World Health Organization. Table 2. Criteria for the Histologic Diagnosis of Neuroendocrine Tumors Typical carcinoid Carcinoid morphology Less than 2 mitoses per 2 [mm.sup.2] (10 HPFs) * No necrosis 0.5 cm or larger Atypical carcinoid Carcinoid morphology 2-10 mitoses per 2 [mm.sup.2] (10 HPFs) OR Necrosis (often punctuate) Large cell neuroendocrine carcinoma Neuroendocrine morphology: organoid nesting, rosettes, palisading, trabeculae High mitotic rate: 11 or greater per 2 [mm.sup.2] (10 HPFs), median of 70 per 2 [mm.sup.2] (10 HPFs) Necrosis (often large zones) Cytologic features of non-small cell carcinoma (NSCLC): large cell size low nuclear to cytoplasmic ratio vesicular, coarse or fine chromatin, and/or frequent nucleoli (some tumors have fine nuclear chromatin and lack nucleoli, but qualify as NSCLC because of large cell size and abundant cytoplasm) Positive immunohistochemical staining for one or more neuroendocrine markers (other than neuron specific enolase) and/or neuroendocrine granules by electron microscopy Small cell carcinoma Small cell size (less than the diameter of 3 small resting lymphocytes) High nuclear to cytoplasmic ratio Finely granular nuclear chromatin, absent/inconspicuous nucleoli High mitotic rate: 11 or greater per 2 [mm.sup.2] (10 HPFs), median of 80 per 2 [mm.sup.2] (10 HPFs) Frequent necrosis (often large zones) * On some microscopes 2 [mm.sup.2] does not equate to 10 high-power fields (HPFs); explanation of HPF area and mitosis counting is given in Travis et al. (1(p10)) Reprinted with permission from the World Health Organization. Table 3. Staging of Small Cell Lung Cancer * Limited disease (equivalent to TNM stage I-III) Disease restricted to one hemithorax with regional lymph node metastases: Hilar ipsilateral and contralateral Mediastinal ipsilateral and contralateral Supraclavicular ipsilateral and contralateral Ipsilateral pleural effusion Extensive disease (equivalent to TNM stage IV) Sites of disease beyond that of limited disease * Reprinted from Travis et al,2 with permission from the World Health Organization.
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