Update in neoplastic lung diseases and mesothelioma.
Context.--Lung cancer is a common disease frequently seen by the
surgical pathologist. Although secondary to improvements in screening
and radiologic techniques and aggressive resection of small pulmonary
nodules, the diagnosis of preneoplastic lesions is increasing in
frequency and importance. Consequently, a greater understanding of their
role in the development of lung carcinoma is needed for optimal patient
care. Two lesions often encountered as small pulmonary nodules are
bronchioloalveolar carcinoma and adenocarcinoma, which can be
challenging to distinguish. Recently, updates to the TNM classification
of non-small cell lung carcinoma have been reported that directly impact
prognosis and treatment algorithms. Identification of new molecular
targets in pleural mesothelioma and in preneoplastic lesions may lead to
improved therapeutic strategies.
Objective.--To present recent advances in our understanding of neoplastic lung diseases and mesothelioma and to describe how these advances relate to the current practice of pulmonary pathology.
Data Sources.--Published literature from PubMed (National Library of Medicine) and primary material from the authors' institution.
Conclusions.--It is important for the surgical pathologist to understand current diagnostic classifications of non-small cell lung cancer and to be aware of the range of preneoplastic lesions, as well as the features useful for distinguishing bronchioloalveolar carcinoma from adenocarcinoma in small pulmonary nodules. Although pleural mesothelioma has distinct features, it can also overlap histologically with adenocarcinoma, and immunohistochemistry can greatly aid in accurate diagnosis. New therapies targeting molecular markers in both non-small cell lung cancer and mesothelioma rely on accurate histopathologic diagnosis of these entities.
|Article Type:||Disease/Disorder overview|
Lung cancer, Non-small cell
Lung cancer, Non-small cell (Prevention)
Lung cancer, Non-small cell (Development and progression)
Lung cancer, Non-small cell (Genetic aspects)
Mesothelioma (Development and progression)
Mesothelioma (Genetic aspects)
Alfacalcidol (Health aspects)
Calcifediol (Health aspects)
Vitamin D (Health aspects)
Gordon, Ilyssa O.
Mackinnon, A. Craig
Husain, Aliya N.
|Publication:||Name: Archives of Pathology & Laboratory Medicine Publisher: College of American Pathologists Audience: Academic; Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2009 College of American Pathologists ISSN: 1543-2165|
|Issue:||Date: July, 2009 Source Volume: 133 Source Issue: 7|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
Despite a declining incidence in males, (1) lung cancer continues
to be a common disease which is frequently encountered by the surgical
pathologist. It remains the most common cause of cancer-related death in
the United States and is relatively untreatable, even with more than
1000 currently open clinical trials. (2)
Recent studies have advanced our understanding of the molecular changes underlying the progression of some preneoplastic lesions. These changes may lead to new approaches for lung cancer prevention, such as those using vitamin D. Also, improvements in radiologic detection techniques have led to the discovery of smaller lesions, which may be successfully treated with less rigorous chemotherapeutic and surgical protocols.
Improved radiologic imaging techniques have also affected the clinical staging of lung tumors. Recent recommendations for revisions to the TNM classification and staging system for non-small cell lung carcinoma (NSCLC) attempt to incorporate these new data, with the intent of refining clinical groups to lead to more appropriate therapy for individual patients. New treatment strategies include therapies targeted to specific proteins expressed by the tumor, which can be identified by immunohistochemistry, tissue microarray, tumor protein expression profiling, and other techniques. Some of these therapies may also be useful for malignant pleural mesothelioma (MPM), and are currently being tested in clinical trials. A large body of literature identifies different molecular targets for developing therapeutic interventions, a few of which are in early clinical trials. However, as these are not included in the current standard of care, a detailed discussion will not be presented here.
PREINVASIVE EPITHELIAL LESIONS
The World Health Organization lung classification lists 3 main forms of preinvasive neoplastic lesions: squamous dysplasia and carcinoma in situ, atypical adenomatous hyperplasia, and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH). (3) Identification of pre-invasive lesions supports the concept of a stepwise progression to lung cancer development. (4) Patients with pre-invasive lesions are ideal candidates for chemopreventive therapy, based on molecules which may be involved in the pathogenesis of lung carcinoma, such as vitamin D. (5)
Squamous Dysplasia and Carcinoma In Situ
Mucosal abnormalities that accompany squamous cell carcinoma include basal cell hyperplasia, squamous metaplasia, dysplasia, and carcinoma in situ. These lesions are usually seen in smokers and their frequency correlates with the number of cigarettes smoked. Dysplasia and carcinoma in situ are preinvasive and all are reversible and may regress with the cessation of smoking. (6) However, some studies have shown that approximately 25% of dysplastic lesions progress to invasive carcinoma during a mean period of 36 months, while in more than 50% of patients with carcinoma in situ, the disease was found to progress to invasive carcinoma within 30 months. (7,8)
Chronic irritation and stimulation (eg, from smoking) results in hyperplasia of multipotent progenitor basal cells residing in the respiratory epithelium (basal cell hyperplasia). Basal cells can also differentiate toward the squamous phenotype (squamous metaplasia), an adaptation favoring survival and protection in a harsh environment. Normally, there are no squamous cells in the airways. Persistent insults cause cellular damage, resulting in squamous dysplasia and carcinoma in situ. (8-10)
Grossly, the lesions of squamous dysplasia and carcinoma in situ are not visible. However, the use of fluorescent bronchoscopy such as lung-imaging fluorescent endoscopy has increased the sensitivity of detection. Seventy-five percent of lesions are flat or superficial, while 25% are nodular or polypoid. (8,9)
Mild squamous dysplasia is characterized by a minimal alteration of cytology and architecture of the bronchial epithelium. The basal zone is expanded but limited to the lower third of the epithelium. The cells are vertically oriented and mitoses are absent. Moderate dysplasia shows more cytologic atypia but the cells remain vertically oriented. The basal zone is expanded to two-thirds of the epithelium and mitotic figures are limited to the expanded basal zone. Severe dysplasia exhibits significant cytologic atypia with little cell maturation. The basal zone is expanded to the upper third of the epithelium with flattening of the superficial cells. Mitotic figures are present within the expanded basal zone. Carcinoma in situ usually arises near bifurcations in the segmental bronchi and extends proximally into adjacent lobar bronchi and distally into subsegmental branches. (8,9) This lesion is characterized by monotonous cells with cytologic atypia, coarse nuclear chromatin, and mitotic figures throughout the epithelium. There is no maturation of the epithelium, and there may or may not be epithelial thickening. (6,8-10) Overlap between dysplasia and carcinoma in situ is considerable and in many cases a range of dysplasia is seen (Figure 1, A through D).
Current theories for the pathogenesis of squamous cell carcinoma describe a progression of genetic changes which begin in the normal epithelium and increase in severity in the dysplastic epithelium. The mutations follow a sequence with allelic losses at multiple 3p sites (3p21, 3p14, 3p22-24, and 3p12) and loss of heterozygosity at chromosome 9p21 (CDKN2A) as the early changes. (8,9) Later, changes at 8p21-23, 13q14 (retinoblastoma), and 17p13 (TP53) occur. (8,9) Precursor lesions show more focal losses, whereas advanced tumors show complete or partial loss of chromosomal arms. (6)
Atypical Adenomatous Hyperplasia
Atypical adenomatous hyperplasia (AAH) is considered to be the adenoma in the adenoma-carcinoma sequence leading to bronchioloalveolar carcinoma (BAC) and invasive adenocarcinoma of the lung. Atypical adenomatous hyperplasia is defined by the World Health Organization as a localized proliferation of mild to moderately atypical cells lining involved alveoli, and sometimes respiratory bronchioles, resulting in focal lesions in peripheral alveolated lung that are usually less than 5 mm in diameter. (3)
Atypical adenomatous hyperplasia consists of peripheral lesions, found in centriacinar regions close to terminal and respiratory bronchioles, that arise from bronchioloalveolar epithelium. (8,9) The lesions can be single or multiple and may appear as ground-glass opacities on computed tomography of the chest, but are usually incidental findings in up to 40% of lungs resected for other reasons, usually adenocarcinoma (6,8,9) and, less commonly, squamous cell carcinoma.
Grossly, AAH may be visible as discrete gray to yellow foci although they are difficult to see on casual inspection. Larger lesions with greater thickening of the alveolar walls by collagen may be seen if the lung is well inflated and fixed in formalin. (10) They range in size from 1 to 10 mm with most being less than 3 mm. (8,9)
Microscopically, AAH is characterized by alveolar septa lined by rounded, cuboidal, low columnar cells with round to oval nuclei showing either Clara cell or type II pneumocyte differentiation. Intranuclear inclusions can be seen in up to 25% of cells. Ciliated and mucin-producing cells are absent and mitoses are extremely rare. Most cases show a discontinuous lining of septa with cells having minimal atypia, while some cases show cells with more continuous and moderate atypia. The cells "respect each other's borders" and gaps between cells are often seen (Figure 2, A and B). Pseudopapillae and tufts may be present. Alveolar septa may be thickened by collagen, fibroblasts, and lymphocytes. (6)
Molecular changes present in smoking-related lung adenocarcinomas are also present in AAH, further supporting the idea that AAH is a preneoplastic lesion. One of the most significant is the presence of KRAS mutations, which are frequent in lung adenocarcinomas and seen in up to 39% of AAH cases. (9) Other abnormalities include overexpression of cyclin D1 (70%), p53 (10%-58%), survivin (48%), and HER2/neu (7%) proteins. (9) Additionally, in some cases, AAH is associated with loss of heterozygosity of chromosomes 3p (18%), 9p (CDKN2A;13%), 9q (53%), 17q, and 17p (TP53; 6%), changes that are also found in lung adenocarcinomas. (8,9) In addition, loss of LKB1, a serine/threonine kinase tumor suppressor gene, has been described in lung adenocarcinomas as well as in AAH with severe cytologic atypia (21%) and is a rare finding in AAH with mild atypia (5%). (8,9) These data suggest that LKB1 may play a role in AAH progression to malignancy. (8,11) Interestingly, molecular changes found in nonsmoking-related lung cancers, including epidermal growth factor receptor (EGFR) mutations, are infrequent in AAH. (8,12,13)
The differential diagnosis of AAH includes reactive pneumocyte hyperplasia, peribronchiolar metaplasia, and BAC. Reactive pneumocyte hyperplasia is associated with parenchymal inflammation, fibrosis, and obvious lung injury. The diagnosis of AAH cannot be made in this context. Reactive pneumocytes do not form discrete lesions and are diffusely distributed. Cytologic atypia is unusual, except when associated with chemotherapy or radiation, where single cells with bizarre nuclei can be seen. (6) Peribronchiolar metaplasia is also a reaction to injury resulting in fibrosis. However, in contrast to AAH, the cells lining alveoli in this entity are ciliated, bronchiolar-type cells. (6) Bronchioloalveolar carcinoma shows morphologic overlap with AAH, and it has been suggested that these lesions are part of the continuum in the adenoma-carcinoma sequence of the development of lung adenocarcinoma. Bronchioloalveolar carcinoma measures more than 5 mm and shows monotonous cellular proliferations, which overlap and have mild stratification. Goblet cells may be seen in BAC and are absent in AAH. Bronchioloalveolar carcinoma usually shows an abrupt transition to adjacent alveolar-lining cells, while AAH often blends imperceptibly into the adjacent alveoli. (6,8-10)
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Diffuse Idiopathic Pulmonary Neuroendocrine Cell Hyperplasia
Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia is a rare lesion that is regarded as a precursor to low-grade, peripherally localized, carcinoid tumors. The relationship between DIPNECH to more central, highgrade neuroendocrine tumors is unclear. (10)
Grossly, DIPNECH lesions are not visible. As they progress to carcinoid tumorlets and tumors they appear as small, well-demarcated, gray-white nodules resembling "miliary bodies." Microscopically, DIPNECH lesions are seen as a widespread proliferation of pulmonary neuroendocrine cells with patterns that include individual cells, small groups, or nests. Proliferation is centered in the bronchial or bronchiolar epithelium (Figure 3, A and B). Nodules of neuroendocrine cells can protrude into airway lumina causing occlusion. As the lesions advance, the neuroendocrine cells break through the basement membrane and form 2 to 5 mm carcinoid tumorlets, often with associated fibrosis. Aggregates of neuroendocrine cells greater than 5 mm are regarded as typical carcinoid tumors. (6,8-10)
BRONCHIOLOALVEOLAR CARCINOMA AND
A landmark study of small (<2 cm) peripheral adenocarcinomas by Noguchi et al (14) defined the prognostic significance of the lepidic growth pattern and lack of invasion seen in BAC. Since then, recognition of BAC as a noninvasive tumor distinct from small adenocarcinomas with areas of BAC-like architecture has continued to evolve. Classic BAC presents in a wide age distribution and is not strongly associated with smoking. The location is usually peripheral, and the defining microscopic feature is that of neoplastic cells growing along preexisting alveolar septa with no evidence of invasion (ie, lepidic growth pattern). Three-quarters of BACs are nonmucinous type (Figure 4) and most likely arise from foci of AAH, and one-quarter are mucinous type (Figure 5), with tumor cells resembling endocervical or goblet cells. A diagnostic pitfall may occur in the interpretation of the immunophenotype because mucinous BAC often expresses both cytokeratin (CK) 7 and CK20, but not thyroid transcription factor 1, and so may be mistaken for a metastatic gastrointestinal tumor. (15) CDX2, an intestinal epithelial marker of proliferation and differentiation, may be useful as it is expressed in metastatic colorectal adenocarcinoma but not in BAC, (16) although its expression in primary pulmonary mucinous carcinomas still presents a diagnostic dilemma. (17) Classic histologic architectural features and lack of invasion can aid in the diagnosis. Nonmucinous BAC expresses CK7 and thyroid transcription factor 1, but not CK20, similar to primary pulmonary adenocarcinoma.
Several studies have investigated various aspects of small adenocarcinomas and BACs. The consensus is that small tumors with pure BAC, or those with alveolar collapse or sclerosis, are not likely to be invasive or metastatic (18) and can be resected with no expectation of recurrence and with excellent prognosis for patient survival. (19) The same excellent survival that is observed in cases with pure BAC tumors is seen even for tumors with questionable single-cell invasion, as well as minimal stromal invasion in areas of BAC pattern (Figure 6) or at the edges of fibrotic areas. (18,20) In one study by Terasaki et al, (18) small adenocarcinomas, with up to 5 mm of contiguous linear invasion, had no lymph node metastases, similar to pure BAC.
In small adenocarcinomas with definitive invasion, those tumors with minimal or with no BAC-like component were found to be more aggressive than those classified as mixed BAC pattern (at least 10% lepidic growth pattern). (21) Interestingly, male smokers with small adenocarcinomas were more likely to have the more aggressive tumor patterns, (22) and outcomes were the most dire for patients with the heaviest smoking history. (23) Tumors with mixed BAC pattern and definitive invasion demonstrate increased frequency of lymphatic and pleural invasion, (18) and tumors with less BAC-like component were more likely to recur. (24) The presence of micropapillary pattern, found in more than half of small adenocarcinomas in one study, was associated with an almost 50% decrease in 5-year survival when present in mixed BAC-pattern tumors and was also significantly associated with pleural invasion and lymph node metastases. (25) Okudera et al (26) showed evidence of increased vessel density in the central fibrotic areas of small adenocarcinomas, which was associated with decreased disease-free survival, suggesting that the presence of central fibrosis may be a poor prognostic factor because of its association with lymphangiogenesis and angiogenesis.
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There have been several recent studies assessing the presence of EGFR mutations in BAC and in adenocarcinomas with a BAC-like component. Mucinous BAC and adenocarcinoma with a mucinous BAC-like component more often contain EGFR mutations, but not KRAS mutations, while nonmucinous BAC and adenocarcinoma with a nonmucinous BAC-like component more often harbor a KRAS mutation, but not EGFR mutations. (27,28) Thus, careful histologic descriptions in the diagnostic report can aid clinicians in determining when to treat with tyrosine kinase inhibitors (29) and potentially avoid the need for outright EGFR gene analysis. (28) The difference in the gene mutation pattern of mucinous and nonmucinous BAC also emphasizes the concept that these 2 tumors are distinct entities despite similar histologic growth patterns. (29)
In summary, these studies support a strict histopathologic definition of BAC, allowing for only certain minimal amounts of invasion. Synoptic summaries should include a comment on the amount of BAC-like component, as well as the presence of micropapillary component, as these variables can aid the clinician in determining each patient's prognosis. Because the diagnosis of BAC essentially depends on not finding significant invasion, these tumors should be entirely submitted for histologic evaluation, and BAC should never be diagnosed on transbronchial or needle biopsies. (30)
Chemopreventive Therapy and Vitamin D
The concept of chemoprevention for lung carcinoma involves exploring the mechanism of action of agents with suspected antineoplastic properties in murine models and human cell lines, as well as identifying molecules in human preinvasive and invasive lung lesions that can be specifically targeted to prevent growth progression. Because smokers constitute a known high-risk population for the development of certain types of lung cancer, the development of murine lung tumors by using a known tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, also called NNK, has become a refined model for the testing of chemopreventive agents. (31) Agents with chemopreventive effects in this and other murine models include 8-methoxypsoralen, (31) farnesol, (32) fatty acid synthase inhibitors, (33) and compounds found in fruits and vegetables, such as hespiridin (34) and quercetin. (35) A compound in green tea, epigallocatechin gallate, or EGCG, along with caffeine, has also been shown in murine lung carcinoma models to inhibit the progression of development of adenocarcinoma from adenoma (36) and to reduce oxidative damage to DNA. (37) The addition of atorvastatin to epigallocatechin gallate and caffeine had synergistic effects on tumor cell apoptosis. (38) The immune system may also be a valuable target for lung cancer chemoprevention, with ongoing clinical trials assessing agents that target the cyclooxygenase-2 pathway (39), and with a decreased incidence of lung cancer in patients with chronic obstructive pulmonary disease who take high-dose corticosteroids. (40)
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The expanding body of literature (reviewed by Ingraham et al (5)) describing vitamin D as a protective molecule against cancer has illustrated its role in the regulation of cellular processes involved in tumorigenesis and metastasis. Various aspects of the vitamin D metabolic pathway have been specifically implicated in lung cancer, including increased levels of cytochrome P24 expression by NSCLC cells, resulting in increased catabolism of vitamin D, (41) and increased levels of circulating 25-hydroxyvitamin D, associated with improved survival in patients with NSCLC. (42) Importantly for its potential use as a chemopreventive agent, the vitamin D receptor is expressed in human NSCLC, as well as metaplastic and dysplastic lesions from bronchial biopsies. (43) Unfortunately, the chemopreventive effects of other vitamins and related compounds studied in clinical trials, including [beta]-carotene, 13-cis-retinoic acid, and [alpha]-tocopherol, have had disappointing results, (44-48) denoting the importance of using appropriate caution when translating findings to the clinical setting.
REVISED TNM CLASSIFICATION FOR NON-SMALL CELL LUNG CARCINOMA
The 7th edition of the TNM Classification of Malignant Tumours will be released in 2009 and will contain revisions to the existing classification for non-small cell lung carcinoma. (49) The current 6th edition of the TNM classification system (50) did not contain any revisions adopted in 1997 by the American Joint Committee on Cancer and the Union Internationale Contre le Cancer. (51) Although it addressed problems of heterogeneity among the outcomes of the different stages of disease, (52) the 1997 classification needed updating based on current information regarding prognostic implications of tumor size, ipsilateral pulmonary nodules, and other pathologic factors. (53) To this end, the International Association for the Study of Lung Cancer created its Lung Cancer Staging Project, which has been acknowledged as the primary source for recommendations on revisions to the current classification system. (49)
The recommended revisions for the TNM staging classification of NSCLC are based on more than 65 000 cases from 19 countries that were diagnosed during the 10-year period from 1990 to 2000, a time during which staging methods included the regular use of computed tomography scans, and for which at least 5 years of follow-up were available. (49) All modifications have undergone intensive validation. (54) The tumor size (T) descriptor has been modified to reflect nuances in tumor size and the presence of additional tumor nodules in the lungs, as these parameters have been found to be related to prognosis. The Table outlines proposed changes to the TNM system that include the following for the T descriptor: T1a ([less than or equal to] 2 cm); T1b (>2 cm but [less than or equal to] 3 cm);T2a (>3 cm but [less than or equal to] 5 cm);and T2b (>5 cm but [less than or equal to] 7 cm) (55); tumors greater than 7 cm with or without additional nodules in the same lobe will now be T3, and those greater than 7 cm with ipsilateral nodules in the nonprimary lobe will be T4. (49,55) Regarding the node (N) component of the TNM system, the current N classifications were found to define distinct prognostic groups, and there was insufficient data to support subdividing the N descriptor. (56) Modifications for the metastasis (M) component have also been recommended: malignant pleural effusions and nodules in the contralateral lung will be categorized as M1a and distant metastases will be M1b. (55,57) A prospective database to further validate these modifications is being developed. (54)
Malignant pleural mesothelioma (MPM) is a rare tumor that has been extensively studied because of its association with environmental exposures, such as asbestos, as well as its extremely poor prognosis. Most MPMs are the epithelioid type, with bland round nuclei, vesicular chromatin, prominent nucleoli, and a moderate amount of cytoplasm. Architecturally, the tumor can grow in papillary, glandular, solid, or mixed patterns. The sarcomatoid type consists of pleomorphic spindle cells in a storiform pattern within a fibrous stroma. Desmoplastic mesothelioma is a variant of the sarcomatoid type with dense collagenous stroma associated with a disordered fascicular growth pattern and tumor necrosis. Biphasic tumors must have both epithelioid and sarcomatoid components, with the minor component representing at least 10% of the tumor area. A proposed diagnostic category of heterologous mesothelioma contains malignant heterologous elements, such as chondrosarcoma or osteosarcoma, in addition to the usual mesothelioma features. (58)
The diagnosis of MPM is difficult because of nonspecific clinical symptoms and challenges in obtaining adequate tissue for diagnosis. Initial attempts are typically by cytologic evaluation of pleural effusions, which yield positive results in 30% to 50% of cases. (59) Fluorescence in situ hybridization analysis for a homozygous deletion of the 9p21 locus containing the CDKN2A gene may help distinguish MPM from benign mesothelial proliferations in cytologic specimens. (60) Percutaneous pleural biopsies are diagnostic in about one-third of patients, but often yield little tissue, and thoracoscopic pleural biopsy remains the most effective method of diagnosis. (59)
When diagnostic tissue is obtained, a panel of immunohistochemical markers should be used to distinguish epithelioid MPM from metastatic adenocarcinoma. (61) At least 2 mesothelial markers, such as calretinin, CK5/6, WT1, or D2-40, and 2 carcinoma markers, such as MOC31, BG8, or thyroid transcription factor-1 in cases with a lung primary tumor, should be used to support the diagnosis (Figure 7, A through E; Figure 8, A through C). Positive markers stain strongly and extensively. If results are discordant or there is less than 10% staining of cells with any of the markers, additional markers can be used. The differential diagnosis of sarcomatoid MPM includes melanoma, and sarcomas such as epithelioid angiosarcoma. Melanoma markers such as HMB-45, Melan-A, and MITF1, and angiosarcoma markers, such as Factor VIII and CD31, can aid in diagnosis. Desmoplastic MPM can be distinguished from chronic fibrosing pleuritis by the finding of definitive invasion into muscle or adipose tissue, which can often be better visualized with cytokeratin immunohistochemical staining. Reactive mesothelial proliferations can also be ruled out by finding definitive invasion of mesothelial cells. Also, the combination of cytoplasmic desmin staining, more often seen in reactive mesothelium, and diffuse membranous epithelial membrane antigen staining and/or GLUT1 staining, suggestive of epithelioid MPM, can help support the diagnosis.
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The pathophysiologic mechanism of MPM development is incompletely understood. Numerous studies have explored the role of various types of asbestos fibers in both MPM and other asbestos-related lung diseases. A recent study by Yang et al (62) demonstrated that asbestos-induced production of tumor necrosis factor [alpha] and subsequent signaling through nuclear factor [kappa]B resulted in increased proliferation of mesothelial cells in culture. The role of SV40, a virus contaminant in some polio vaccines,63 is not clear, although Kroczynska et al64 recently showed that SV40 is indeed an asbestos cocarcinogen. More study is needed to further elucidate the mechanisms involved in MPM pathophysiology, and the recent development of the National Mesothelioma Virtual Bank, which contains both clinical data and accessibility to human MPM specimens, will be a rich resource for future translational research studies. (65)
A major area of MPM research has been the identification of overexpressed proteins that may be potential therapeutic targets. For some of these targets, therapeutic agents have already been developed for use in other malignancies. Overexpression of EGFR, (66) vascular endothelial growth factor, (67) and mesenchymal-epithelial transition factor (68) has been shown in the epithelioid variant of MPM. Protein kinase C-[beta], which can signal through nuclear factor [kappa]B, has been shown to be overexpressed in human MPM, and its positive effects on cell migration can be overcome in vitro by the protein kinase C inhibitor enzastaurin. (69) The G protein-coupled receptors for lysophosphatidic acid, LPA1 and LPA2, which can signal through nuclear factor [kappa]B or Akt, were recently shown by Yamada et al (70) to be expressed in MPM cell lines and human samples, and the addition of LPA enhanced cell proliferation and motility via LPA1 and LPA2, respectively. YAP1, another Akt signaling pathway molecule important for apoptosis of damaged cells and involved in mesothelial cell growth, has been shown to be overexpressed in MPM cell lines. (71) Other potential therapeutic targets over-expressed in MPM include MUC1, (72) p21/WAF1, (73) the nicotinic acetylcholine receptor, (74) and several others. (75)
Pathologists may increasingly be asked to perform immunohistochemistry analysis to assess for potential prognostic markers in MPM patients. The presence of intratumoral [CD8.sup.+] T lymphocytes has been found to be associated with improved survival in patients with MPM. (76) Expression of activated cSrc, which can signal through nuclear factor [kappa]B and affects a variety of cellular processes involved in malignancy, has been shown to correlate with advanced-stage MPM. (77) Expression of EGFR, although correlated with epithelioid histology and intratumoral necrosis, has not been shown to be an independent prognostic factor in MPM in one study. (78) On the other hand, Baldi et al (79) found EGFR expression to negatively correlate with survival, along with advanced tumor stage, lymph node involvement, and the sarcomatoid variant. Occult disease in both resection margins from extrapleural pneumonectomy and lymph nodes also negatively impacts survival, and the use of immunohistochemistry should be considered strongly for evaluating these specimens when no tumor is identified in hematoxylin-eosin preparations. (80)
In summary, MPM is a rare disease with uncertain pathophysiologic appearance and recent data suggest that a variety of cell proteins with possible therapeutic or prognostic implications may lead to better treatment. Pathologists must be aware of these entities to facilitate communication and extend optimized information to patients.
Although the overall survival for patients diagnosed with lung cancer (15%) has remained essentially unchanged during the last 20 years, a better understanding of the molecular events involved in the development of lung cancer should ultimately lead to improved therapies. Accurate diagnosis of preinvasive and small malignant lesions will identify groups of patients who may benefit from specialized therapeutic interventions. Also, prognostically relevant revisions to the TNM classification for NSCLC will aid in the accurate interpretation of the effects of novel therapies for patients with more advanced disease. The identification of therapeutic targets in MPM is also valuable, as the consequences of asbestos exposure continue to be seen around the world.
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Ilyssa O. Gordon, MD, PhD; Stephanie Sitterding, MD; A. Craig Mackinnon, MD, PhD; Aliya N. Husain, MD
Accepted for publication December 11, 2008.
From the Department of Pathology, University of Chicago, Chicago, Illinois.
Presented in part at the Biennial Meeting of the Pulmonary Pathology Society, Sante Fe, New Mexico, June 2007.
The authors have no relevant financial interest in the products or companies described in this article.
Reprints: Aliya N. Husain, MD, Department of Pathology, University of Chicago, MC6106, Room S627, 5841 S Maryland Avenue, Chicago, IL 60637 (e-mail: firstname.lastname@example.org).
Proposed Modifications to the TNM Classification System for Non-Small Cell Lung Carcinoma AJCC 6th Edition IASLC Proposed TNM Classification for Cancer Staging AJCC 7th Edition Cancer Staging Manual TNM Manual (49,a) (Specific Revision) Classification (Specific Feature to Be Revised) T1 (tumor S3 cm) T1a (tumor S2 cm) T1b (tumor >2 cm but S3 cm) T2 (tumor >3 cm) T2a (tumor >3 cm but S5 cm) T2b (tumor >5 cm but S7 cm) T4 (separate tumor T3 (tumor >7 cm, [+ or -] nodule[s] in additional nodules in same lobe) same lobe) T4 (any size), M1 T4 (tumor >7 cm, with ipsilateral (separate tumor nodule[s] in nonprimary lobe) nodule[s] in ipsilateral nonprimary lobe) T4 (tumor with malignanM1a (malignant pleural or pericardial effusion) M1 (tumor nodule[s] in M1a (tumor nodule[s] in contralateral lung) M1 (distant metastasis)M1b (distant metastasis) Abbreviations: AJCC, American Joint Committee on Cancer; IASLC, International Association for the Study of Lung Cancer. (a) Note: AJCC 7th edition of Cancer Staging Manual is expected to be published in 2009.
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