Immunocytochemical localization of neuron specific enolase in small cell carcinomas and carcinoid tumours of the lung

Carcinoid tumours and small cell carcinomas of the lung share many characteristics with normal neuroendocrine cells. While carcinoid tumours contain many dense-cored neurosecretory granules and are frequently argyrophil, small cell carcinomas are poorly granulated and rarely argyrophil, which casts doubt on their neuroendocrine nature. Immunostaining of the enzyme neuron specific enolase (NSE) was recently used to demonstrate the neuroendocrine components of the lung including nerves and neuroendocrine cells. We therefore used NSE immunostaining to investigate neuroendocrine differentiation in 79 lung tumours, including 18 bronchial carcinoids and 31 small cell carcinomas, and compared these results with those obtained with silver stains. Thirteen of the 18 carcinoids were reactive to silver, all other types being negative. NSE-immunoreactivity occurred in 16 carcinoids and 18 small cell carcinomas. None of the squamous cell carcinomas, large cell anaplastic carcinomas and adenocarcinomas examined showed NSE-immunoreactivity. Radioimmunoassay of extractable NSE from 10 fresh lung tumours correlated well with the immunostaining results, demonstrating large amounts in two small cell carcinomas (334 and 517 ng/mg protein) and three carcinoids (152, 908, and 1143 ng/mg protein). Values were much lower for four squamous cell carcinomas (31-44 ng/mg protein) and one large cell anaplastic carcinoma (30 ng/mg protein) and were accounted for by the presence of NSE-positive nerves and neuroendocrine cells in the surrounding lung. NSE immunostaining is a useful marker of neuroendocrine differentiation in lung tumours and should prove particularly valuable in the diagnosis of small cell anaplastic tumours and their metastases.     

Immunoexpression of villin in neuroendocrine tumors and its diagnostic implications.

BACKGROUND: Villin, a 95-kd cytoskeletal protein associated with axial microfilament bundles of brush border microvilli, is mostly restricted to intestinal glandular tumors. Villin immunoexpression was recently observed in a small number of carcinoids of the intestinal tract and lung, but its significance in a broad category of neuroendocrine tumors has not been evaluated. DESIGN: A total of 114 neuroendocrine tumors of different origins were tested for villin expression. They included gastrointestinal carcinoids (n = 30), lung carcinoids (n = 15), small cell carcinomas of the lung (n = 24), small cell carcinomas of other sites (n = 15), islet cell tumors (n = 8), Merkel cell carcinomas (n = 6), paragangliomas (n = 6), and others (n = 10). Nine round cell sarcomas were tested as well. RESULTS: Villin immunoreactivity was present in 85% of gastrointestinal carcinoids and small cell carcinomas, but was found in only 40% of lung carcinoids. Other tumors tested were virtually negative for villin. In general, while cytoplasmic reactivity was most common, a characteristic apical membranous pattern simulating brush border was seen in 76% of the gastrointestinal carcinoids and in 50% of the lung carcinoids. CONCLUSIONS: We found that villin was predominantly restricted to gastrointestinal neuroendocrine tumors (excluding islet cell tumors), although a small number of bronchial carcinoids may be positive as well. These results suggest a role for villin in the differential diagnosis of neuroendocrine tumors.     

Expression of the alpha subunit of human chorionic gonadotropin in normal and neoplastic neuroendocrine cells. An immunohistochemical study

The alpha subunit of human chorionic gonadotropin (HCG) was localized Immunohistochemically in paraffin sections of normal human tissues and neuroendocrine tumors. A small subset of dispersed neuroendocrine cells was positive in normal adult tissues, including gastric antrum, urachal remnant, anal glands and prostate. Positive cells were consistently present in perinatal lung but rare in adult lung. In contrast, the beta subunit was absent from these cells. Seventy-two of 151 extrapituitary neuroendocrine tumors (48%) were alpha subunit-positive. Thirty-three of 37 bronchial carcinoids (92%) were immunoreactive, with a high percentage of the tumors (54%) containing moderate to large numbers of positive cells. The alpha subunit was further demonstrated in 9 of 45 small cell lung carcinomas (20%), 19 of 35 extrapulmonary carcinoids (54%), 3 of 11 islet cell tumors (27%) and 8 of 13 medullary thyroid carcinomas (62%). Two of three malignant islet cell tumors were positive. Positive cells were usually few in number, except for two small cell lung carcinomas, two rectal carcinoids, one thymic carcinoid and one malignant islet cell tumor. Pheochromocytomas (n = 10) were negative. Eleven of 19 pulmonary tumorlets (58%) were alpha subunit-immunoreactive. A few beta subunit-positive cells were detected in only 6 lung lesions. The physiological significance of the imbalance of expression of HCG subunits by certain neuroendocrine cells and their tumors remains unknown.     

JLP5B9: new monoclonal antibody against polysialylated neural cell adhesion molecule is of value in phenotyping lung cancer

Non-small-cell lung cancer (NSCLC) is currently one of the most prevalent malignant tumors. It displays a wide variety of phenotypes which includes neuroendocrine markers commonly found on small-cell lung cancers (SCLC) such as the neural cell adhesion molecule (NCAM) and in particular its highly polysialylated isoform, embryonic NCAM (eNCAM). NSCLC with neuroendocrine differentiation may represent a subset of tumors whose cells have a more aggressive biological behavior. A tumor marker that distinguishes this latter sub-type could be of clinical relevance. Accordingly, we have raised a monoclonal antibody of the IgM type (JLP5B9) directed against capsular polysaccharides of N. meningitidis B which bears polysialic acid groups. We have demonstrated that JLP5B9 recognizes eNCAM with high affinity and that it is specifically directed against the polysialic acid moieties of NCAM. JLP5B9 was also found to react with human SCLC, NSCLC and neuroblastoma cell lines. We then used JLP5B9 as a specific probe for the detection of tissue eNCAM and found that it was expressed on up to 20% of tumor cells obtained from 5 out of 13 patients with NSCLC. This mAb deserves further investigation to evaluate its potential as a tool for serodiagnosis of lung cancer.     

Expression of the Alpha Subunit of Human Chorionic Gonadotropin in Normal and Neoplastic Neuroendocrine Cells

The alpha subunit of human chorionic gonadotropin (HCG) was localized Immunohistochemically in paraffin sections of normal human tissues and neuroendocrine tumors. A small subset of dispersed neuroendocrine cells was positive in normal adult tissues, including gastric antrum, urachal remnant, anal glands and prostate. Positive cells were consistently present in perinatal lung but rare in adult lung. In contrast, the beta subunit was absent from these cells. Seventy two of 151 extrapituitary neuroendocrine tumors (48%) were alpha subunit positive. Thirty three of 37 bronchial carcinoids (92%) were immunore-active, with a high percentage of the tumors (54%) containing moderate to large numbers of positive cells. The alpha subunit was further demonstrated in 9 of 45 small cell lung carcinomas (20%), 19 of 35 extrapulmonary carcinoids (54%), 3 of 11 islet cell tumors (27%) and 8 of 13 medullary thyroid carcinomas (62%). Two of three malignant islet cell tumors were positive. Positive cells were usually few in number, except for two small cell lung carcinomas, two rectal carcinoids, one thymic carcinoid and one malignant islet cell tumor. Pheochromocytomas (n=10) were negative. Eleven of 19 pulmonary tumorlets (58%) were alpha subunit immunoreactive. A few beta subunit positive cells were detected in only 6 lung lesions. The physiological significance of the imbalance of expression of HCG subunits by certain neuroendocrine cells and their tumors remains unknown. Acta Pathol Jpn 39: 413 419, 1989.     

Gastrin-releasing peptide gene expression in small cell and large cell undifferentiated lung carcinomas.

Gastrin-releasing peptide (GRP; mammalian bombesin) is present in the neuroendocrine cells of human fetal lung and in small cell lung carcinomas (SCLCs), where it may act as a growth factor. Considering the potential importance of GRP as a tumor marker, we have conducted a retrospective immunohistochemical analysis of 176 lung tumors for markers of GRP gene expression, as well as several other markers of neuroendocrine cell differentiation: chromogranin A, neuron-specific enolase, and calcitonin. The majority of carcinoids contained mature GRP, in contrast to only a minority of SCLCs and large cell lung carcinomas (LCLCs). However, a majority of SCLCs and LCLCs contained proGRP immunoreactivity. In situ hybridization did not add any information beyond what was obtained using proGRP antisera. In spite of sharing these neuroendocrine cell markers, SCLCs are associated with a graver prognosis than LCLCs. No prognostic significance was associated with immunostaining for GRP or several other markers of neuroendocrine cell differentiation.     

Histidine decarboxylase expression as a new sensitive and specific marker for small cell lung carcinoma.

Histidine decarboxylase is one of the enzymes of the amine precursor uptake and decarboxylation system and is known to be distributed in mast cells and enterochromaffin-like cells. With the hypothesis that histidine decarboxylase expression is a marker for neuroendocrine differentiation, we studied the immunoreactivity of histidine decarboxylase in neuroendocrine cells and tumors of the thyroid gland, adrenal medulla, lung, and gastrointestinal tract. Formalin-fixed paraffin sections were subjected to immunohistochemistry using anti-histidine decarboxylase antibody, and the sensitivity and specificity were compared with those of conventional neuroendocrine markers (CD56, chromogranin A, synaptophysin, and neuron-specific enolase). Enterochromaffin or enterochromaffin-like cells, adrenal chromaffin cells, and thyroid C-cells were positive for histidine decarboxylase, and related tumors (carcinoid tumor, pheochromocytoma, medullary carcinoma) showed a high percentage of positive staining. Furthermore, we used the antibody to distinguish small cell lung carcinoma from non-neuroendocrine lung carcinoma and also to detect neuroendocrine differentiation in large-cell neuroendocrine carcinoma and gastrointestinal small-cell carcinoma. The anti-histidine decarboxylase antibody stained most small cell lung carcinoma (18 of 23, sensitivity 0.78), and was rarely reactive with non-neuroendocrine lung tumors (2 of 44; specificity, 0.95). These values were close to those obtained from CD56 staining (sensitivity/specificity, 0.87/0.98). Histidine decarboxylase was also positive for 6 of 12 large cell neuroendocrine carcinomas and 4 of 7 gastrointestinal small cell carcinomas. In conclusion, we demonstrated that histidine decarboxylase is useful to distinguish between small cell lung carcinoma and non-neuroendocrine carcinoma and to demonstrate neuroendocrine differentiation.     

Abnormal p53 expression in lung neuroendocrine tumors. Diagnostic and prognostic implications.

The diagnostic and prognostic implications of p53 immunostaining have been investigated in 59 pulmonary neuroendocrine tumors, including typical carcinoids (n = 15), so-called "atypical carcinoids" (n = 22), and small cell lung carcinomas (SCLCs; n = 22). Immunocytochemistry was performed on formalin-fixed, paraffin-embedded samples using the monoclonal antibody PAb1801, which has been shown to be suitable for staining fixed and embedded tissue sections. p53 immunoreactivity was restricted to atypical carcinoids (45% of the cases being immunoreactive) and to SCLCs (which were positively stained in 59% of the cases), whereas it was consistently lacking in typical carcinoid tumors. When the group of the so-called "atypical carcinoids" was further reclassified, p53 immunostaining was strictly confined to those cases belonging to the histologically more aggressive subsets (well differentiated neuroendocrine carcinoma subsets II and III). Within the same tumor type, however, p53 immunoreactivity did not correlate with the clinical outcome of the disease and was not predictive of the length of survival. The data indicate that abnormal p53 expression (which is strictly dependent on structural abnormalities of the p53 gene) is detectable in the majority of neuroendocrine carcinomas of the lung and might represent a useful adjunct in the differential diagnosis of pulmonary neuroendocrine neoplasms, particularly in routinely fixed and embedded small bronchoscopic biopsies.     

Malignancy-associated X chromosome allelic losses in foregut endocrine neoplasms: further evidence from lung tumors.

Association of X chromosome allelic losses with tumor malignancy has been identified in foregut but not in midgut endocrine neoplasms. The aim of this study was to investigate the association of deletions on X chromosome with malignancy in lung neuroendocrine tumors, another family of foregut neoplasms comprising four categories with increased malignancy: typical and atypical carcinoids, large cell neuroendocrine and small cell lung carcinomas. To evaluate loss of heterozygosity, DNA extracted from nine typical carcinoids, 17 atypical carcinoids, six large cell neuroendocrine carcinomas and five small cell lung carcinomas was PCR-amplified for 18 microsatellite markers spanning the whole X chromosome. All tissue samples were formalin-fixed and paraffin-embedded. X chromosome losses were absent in typical carcinoids, whereas they were found in nine out of 17 atypical carcinoids and in five out of six large cell neuroendocrine carcinomas (involving 28 and 70% of informative loci, respectively). On the contrary, deletions on X chromosome were an extremely rare event in small cell lung carcinomas. In atypical carcinoids, the presence of losses was associated with larger tumor size, higher pT status and advanced stage. No death occurred in atypical carcinoid patients without deletions on X chromosome, whereas all atypical carcinoid patients who had died from disease showed allelic losses. In conclusion, X chromosome allelic losses, absent in benign 'typical' carcinoids, progressively increased in frequency from intermediate-grade 'atypical' carcinoids to high-grade large cell neuroendocrine carcinomas. These results extend the association of deletions on X chromosome with malignancy, already demonstrated in other foregut endocrine neoplasms, to lung neuroendocrine tumors. The absence of X chromosome allelic losses in small cell lung carcinomas underlines a striking difference from large cell neuroendocrine carcinomas, possibly linked to different pathogenetic mechanisms of these two highly aggressive neuroendocrine lung tumors.     

High-grade neuroendocrine carcinomas of the lung highly express enhancer of zeste homolog 2, but carcinoids do not

Enhancer of zeste homolog 2, the catalytic subunit of polycomb repressive complex 2, is a histone methyltransferase and plays an important role in cell proliferation and cell cycle regulation. It has been shown to be overexpressed in a number of malignant neoplasms. This study aimed to determine the expression pattern of enhancer of zeste homolog 2 in neuroendocrine tumors of the lung and the potential of enhancer of zeste homolog 2 to serve as a biomarker to segregate carcinoids from high-grade neuroendocrine carcinomas. Fifty-four cases, including 25 typical carcinoids, 7 atypical carcinoids, 9 large-cell neuroendocrine carcinomas, and 13 small-cell lung carcinomas, were immunohistochemically studied using a monoclonal antibody against enhancer of zeste homolog 2. All 13 small-cell lung carcinomas demonstrated moderate to strong nuclear staining with 12 exhibiting more than 90% of tumor cells staining. All 9 large-cell neuroendocrine carcinomas were moderately to strongly positive for enhancer of zeste homolog 2, with 6 cases having staining in more than 80% of tumor cells. In contrast, all 25 typical carcinoids and 6 atypical carcinoids showed only rare scattered enhancer of zeste homolog 2-positive tumor cells, with 1 case of atypical carcinoid exhibiting moderate staining in 40% of tumor cells. A subsequent validation study of the 14 specimens of lung or mediastinal lymph node biopsy and fine-needle aspiration, including 6 small-cell lung carcinomas, 2 large-cell neuroendocrine carcinomas, 5 typical carcinoids, and 1 atypical carcinoid, was performed. Enhancer of zeste homolog 2 was diffusely and strongly positive in all small-cell lung carcinomas and large-cell neuroendocrine carcinomas, even with severe crush artifact, whereas it was only positive in rare tumor cells in carcinoids. These findings support the formulation that enhancer of zeste homolog 2 may play an important role in the regulation of biologic behavior of high-grade neuroendocrine carcinomas and as a diagnostically useful marker in distinguishing high-grade neuroendocrine carcinomas from carcinoids.     

Bcl-2 protein expression in lung cancer and close correlation with neuroendocrine differentiation.

For determination of the cellular distribution of bcl-2 expression in lung cancer and clarification of its correlation with cell neuroendocrine differentiation, Bcl-2 immunostaining was carried out on a large series of formalin-fixed, paraffin-embedded lung cancer samples, and four general neuroendocrine marker and seven peptide hormone stainings were carried out on all Bcl-2-positive squamous cell carcinomas and adenocarcinomas of the lung as well as on 8 pulmonary neuroendocrine carcinomas histologically diagnosed. In addition, 3 small cell lung cancer cell lines were studied by Western blotting. Neuroendocrine differentiation in Bcl-2-negative squamous cell carcinomas and adenocarcinomas was examined with chromogranin A and alpha-subunit of Go protein stainings. Bcl-2 protein was detected in 104/111 small cell carcinomas, 8/8 neuroendocrine carcinomas, 0/6 typical (well differentiated) carcinoids, 23/64 squamous cell carcinomas, 4/65 adenocarcinomas, and all 3 small cell lung cancer cell lines. All 8 neuroendocrine carcinomas, 11 of the Bcl-2-positive squamous cell carcinomas, and all 4 Bcl-2 positive adenocarcinomas expressed multiple neuroendocrine markers. The distributions of Bcl-2 and neuroendocrine marker immunoreactivity closely paralleled each other on consecutive sections. In squamous cell carcinomas, Bcl-2-positive cells could be roughly subdivided into those with neuroendocrine differentiation features, usually demonstrating intense Bcl-2 staining, with basaloid tumor cells usually expressing weak to moderate Bcl-2 staining. The present study clearly shows Bcl-2 protein expression to be remarkably differentially regulated according to histological types of lung cancers and to appear to quite likely be closely associated with neuroendocrine differentiation of tumor cells, indicating that bcl-2 is importantly involved in cell development and differentiation, in addition to protecting cells from apoptosis. Bcl-2 might be usable as a neuroendocrine marker in lung cancers and possibly also in neural-crest-derived tumors.     

Immunohistochemical demonstration of phosphorylated and nonphosphorylated forms of human neurofilament subunits in human pulmonary carcinoids

Using immunohistochemical tests and monoclonal antibodies specific for phosphorylated isoforms of the high-molecular-weight human neurofilament subunit (NF-H) or for nonphosphorylated isoforms of NF-H and the middle-molecular-weight NF protein, we detected phosphorylated and nonphosphorylated NF protein isoforms in typical central bronchial carcinoids but not in atypical or peripheral carcinoids or in small cell undifferentiated carcinomas of the lung. Immunoreactive NF protein was seen largely in juxtanuclear globular aggregates which may correspond to cytoplasmic whorls of intermediate filaments observed in one of the tumors by electron microscopy. A monoclonal antibody to low-molecular-weight keratin polypeptides immunostained similar aggregates in central bronchial carcinoids. The precursor cells of human pulmonary carcinoids and the mechanisms leading to abnormal aggregates of NF and keratin immunoreactivity are unknown. However, the preponderance of phosphorylated NF epitopes as compared with nonphosphorylated forms in the cell bodies of carcinoid tumor cells implicates abnormal phosphorylation states in the formation of these intermediate filament aggregates. Our data do not confirm that antibodies to NF-H are helpful for the diagnosis of undifferentiated lung carcinomas, but they can distinguish subsets of bronchial carcinoids with different biological behaviors and growth potentials.     

P63 expression in lung carcinoma: a tissue microarray study of 408 cases.

p63 is a recently discovered member of the p53 family that has been shown to be important in the development of epithelial tissues. p63 may also play a role in squamous cell carcinomas of the lung, head and neck, and cervix, and its expression is increased in these tumors. The purpose of this study was to investigate the expression of p63 in a broad spectrum of histologic types of lung tumors. A total of 441 cases of primary lung tumors with follow-up data were identified, and the paraffin-embedded tissue blocks were used to construct a duplicate core tissue microarray. After review of the tissue cores, 408 cases, consisting of 123 squamous cell carcinomas, 93 adenocarcinomas, 68 large cell carcinomas, 68 classic carcinoids, 31 atypical carcinoids, 11 large cell neuroendocrine carcinomas, and 14 small cell carcinomas, were adequate for analysis. Immunohistochemistry was performed at 2 different laboratories using monoclonal antibody 4A4 to detect the expression of p63, using different staining protocols. p53 expression was also studied with immunohistochemistry using monoclonal antibody DO-7. Kaplan-Meier curves were plotted to compare the survival of p63-expressing versus nonexpressing tumors. A large proportion of squamous cell carcinomas expressed p63 (96.9%), most showing strong positive nuclear immunoreactivity. Expression in other nonsmall cell lung cancers was also present. Thirty percent of adenocarcinomas and 37% of large cell carcinomas showed p63 expression. In the neuroendocrine tumors, an increasing proportion of tumors stained for p63 as tumor grade increased; 1.9% of classic carcinoids, 30.8% of atypical carcinoids, 50% of large cell neuroendocrine carcinomas, and 76.9% of small cell carcinomas were positive. Approximately half of the positively staining neuroendocrine cases showed strong staining. Expression of p63 was of prognostic significance in neuroendocrine tumors (P < 0.0001), with higher-grade tumors more likely to express p63. Correlation between p63 and p53 expression was not observed (P = 0.18) in nonsmall cell lung cancer; however, a significant correlation between the 2 markers was found in neuroendocrine tumors (P < 0.0001). p63 staining was repeated with a different staining protocol, yielding similar results overall but a lower percentage of positive cases (34.2% vs. 48.4% of tumors positive). In conclusion, p63 expression is consistently expressed in squamous cell carcinoma in the lung, but is also expressed in a subset of adenocarcinomas and large cell carcinomas. Pulmonary neuroendocrine tumors also show p63 staining in some instances, particularly in higher-grade tumors, and the majority of small cell carcinomas are p63-positive. These results suggest that p63 may be involved in oncogenesis in a broader range of tumors than was previously thought.     

Immunohistochemical analysis of calcitonin and calcitonin gene-related peptide in human lung

Calcitonin and calcitonin gene-related peptide (CGRP) have been localized immunohistochemically in neuroendocrine cells of normal and diseased human lungs. Cells immunoreactive for calcitonin and CGRP first appeared in immature bronchi in the 27th gestational week. Thereafter, both peptides were found in the same bronchial neuroendocrine cells throughout fetal and neonatal life. In adult lungs with or without neuroendocrine cell hyperplasia, only calcitonin was present. In 17 of 18 (94%) pulmonary tumorlets, variable numbers of calcitonin-positive cells were identified. A few CGRP immunoreactive cells, as a subset of calcitonin-containing cells, were found in only three (17%) lesions. Of 37 bronchial carcinoids, calcitonin was detected in 14 and CGRP was detected in 16 (38% and 43%, respectively), and both peptides were predominantly localized in the same cells. Ten of 45 (22%) small cell lung carcinomas were calcitonin-immunoreactive. CGRP was noted in only one (2%) of these tumors, and both peptides coexisted in single cells. These findings indicate that the patterns of calcitonin/CGRP expression in hyperplastic bronchial neuroendocrine cells, pulmonary tumorlets, and, to some extent, small cell lung carcinomas are similar to those of normal adult lungs. On the other hand, calcitonin/CGRP expression in bronchial carcinoids is similar to that of late fetal and neonatal lungs.     

Kit expression in small cell carcinomas of the lung: effects of chemotherapy.

A significant number of small cell lung carcinomas shows overexpression of the proto-oncogene c-kit product, a tyrosine kinase known as Kit or CD117. This molecular pathway seems somewhat implicated in promoting the neoplastic growth of small cell lung carcinoma. The current pharmacological availability of its selective inhibitor, together with the promising clinical results in the management of CD117-positive neoplasms such as advanced gastrointestinal stromal tumors, aroused great interest among oncologists in also adopting this therapeutic strategy in other CD117-positive tumors. We evaluated a series of 27 small cell lung carcinomas, comparing the expression of CD117 of the primary na?ve tumor (before first-line chemotherapy) with the expression of the same neoplasm after postchemotherapy relapse. All the patients underwent similar chemotherapeutic regimens (cisplatin/carboplatin plus etoposide). At diagnosis, 21 of 27 cases (78%) showed strong immunoreactivity for CD117. Among these 21 originally positive tumors, CD117 remained overexpressed in 10 after relapse (48%), whereas the other 11 cases became negative. No originally CD117-negative small cell carcinomas displayed immunoreactivity after chemotherapy. CD117 expression was not statistically correlated with overall survival, occurrence of chemoresistance, or clinical response to chemotherapy. We also evaluated CD117 expression in a series of 46 surgically resected non-small cell lung carcinomas (8 squamous cell carcinomas, 10 adenocarcinomas, 5 pleomorphic carcinomas, 10 typical and 3 atypical carcinoids, and 10 large cell neuroendocrine carcinomas). Apart from small cell carcinomas, CD117 overexpression was observed in 6 of 10 large cell neuroendocrine carcinomas, whereas all the other histotypes resulted unstained. We speculate that loss of CD117 expression after chemotherapy in a high proportion of SCLC indicates that in this tumor, Kit unlikely represents the product of a constitutive mutation, as instead shown in gastrointestinal stromal tumors. Keeping this finding in mind, oncologists could re-test CD117 expression in relapsing small cell lung carcinomas in order to establish the best candidates for enrollment in ongoing clinical trials with Kit inhibitors. Practically speaking, CD117 may be helpful in discriminating between pulmonary high-grade neuroendocrine tumors and other histotypes, but pathologists should be aware that treated small cell lung carcinomas may remain unstained in a not insignificant number of cases.     

34betaE12 Cytokeratin Immunodetection in the Differential Diagnosis of Small Cell Tumors of Lung

The group of small cell tumors of the lung includes fine following: (1) small cell carcinoma (SCC) of neuroendocrine (NE) origin, (2) poorly differentiated squamous carcinoma, (3) the rare basaloid (basal cell) carcinomas, and (4) malignant lymphomas, primitive neuroectodermal tumors (PNETs), and rhabdomyosarcomas. The differential diagnosis among these entities carries a heavy therapeutic impact but may be difficult in small biopsy specimens or in cytologic material, especially if necrosis or artifactual alterations are present. The use of additional techniques such as immunostaining for NE markers is not always helpful, since immunoreactive chromogranin A is detectable in only a small percentage of small cell carcinomas. It has recently been reported that in the aerodigestive tract 34betaE12 cytokeratin (CK) immunostaining selectively labels non-NE carcinomas, including squamous cell carcinoma, adenocarcinoma, and the rare basaloid carcinoma. We evaluated the role of such CK immunodetection in the differential diagnosis of small cell lung tumors in cytologic and biopsy specimens. Eighty-one lung tumors diagnosed by means of endoscopic bronchial biopsy, fine needle aspirate, or bronchial washing were collected. They included 43 small cell NE carcinomas and 38 cases used as controls (comprehensive of 2 large cell neuroendocrine carcinomas, 4 carcinoid tumors, 30 cases of non-NE lung carcinomas, 2 cases of bronchial infiltration by non-Hodgkin lymphomas). 34betaE12 CK immunoreactivity was found in 29/30 cases of non-NE carcinomas, but in only 3/43 SCCs. The latter showed positivity in only a few scattered cells. The 2 cases of bronchial infiltration by malignant lymphoma as well as the 4 cases of carcinoid tumors and the 2 cases of large cell neuroendocrine carcinomas were negative. These findings were confirmed in the surgical specimens of operatedon cases. We conclude that, in lung carcinoma biopsies showing a small cell pattern, presence of 34betaE12 CK immunoreactivity favors a non-NE carcinoma, whereas its absence supports the diagnosis of SCC. Int J Surg Pathol 8(4):317-322, 2000