Expression of p53, p21 and bcl-2 in prognosis of lung carcinomas

Expression of suppressor genes 53 and bcl-2 as well as of protein p21 (partly induced by p53 gene) was analyzed in a group of 77 resection specimens and bronchial excision of lung carcinomas (of all basic histological types--squamous cell, neuroendocrine, adenocarcinoma, undifferentiated). Simultaneously the relation of tumor immunophenotype and level of differentiation, cell death and 2-year-survival of patients was evaluated. Gene p53 showed non-only an expected strong expression in squamous cell carcinomas but especially in adenocarcinomas, which were newly characterized by exceptional hyper-expression of p53 in lowly differentiated variants. Expression level of protein p21 and gene p53 was parallel only in adenocarcinomas and undifferentiated carcinomas but discordant in squamous cell and neuroendocrine carcinomas. Positivity of p21 slightly prevailed in well-differentiated variants of the histological types but an exceptional positivity was found even in all the undifferentiated carcinomas. Gene bcl-2 revealed a paradox of strong expression in lowly differentiated neuroendocrine and undifferentiated carcinomas. The level of bcl-2 expression in squamous cell carcinomas was found higher than in references. Among tumors with cell death there was an inverted relation of bcl-2 and p53 expression (high/low) in neuroendocrine carcinomas but both of them were mostly negative in squamous cell carcinomas. A more frequent 2-year-survival of squamous cell carcinomas was verified for bcl-2 positive tumors and newly for p53 positive squamous cell carcinomas. Evaluation of the expression of p53, p21 and bcl-2 in lung carcinomas is so equivocal that its prognostic usage was found to be only complementary to the direct immunohistochemical investigation of the growth activities.     

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.     

Microtubule-associated protein-2: a new sensitive and specific marker for pulmonary carcinoid tumor and small cell carcinoma.

Microtubule-associated proteins (MAPs) are a major component of cytoskeleton family proteins associated with microtubule assembly. MAP-2 has been shown to be specifically expressed in neuronally differentiated cells. Pulmonary neuroendocrine carcinomas such as carcinoid tumors and small cell carcinomas are derived from neuroendocrine cells. We hypothesize that neuroendocrine cells may also express MAP-2, and therefore, MAP-2 may be used as a marker for pulmonary carcinomas of neuroendocrine differentiation. To investigate the utility of using MAP-2 expression to separate pulmonary neuroendocrine from non-neuroendocrine tumors, we examined the expression of MAP-2 immunohistochemically in 100 cases of pulmonary carcinomas. The immunoperoxidase method with antigen retrieval was used to characterize the expression of MAP-2, chromogranin, synaptophysin, and neuron-specific enolase in 25 small cell carcinomas, 25 carcinoid tumors, 25 adenocarcinomas, and 25 squamous cell carcinomas. All tumors were lung primaries. All 25 cases of carcinoid tumors (100%) as well as 23 of 25 cases (92%) of small cell carcinomas were positive for MAP-2. Four of 25 cases (16%) of adenocarcinomas were positive for MAP-2 and synaptophysin. Among the 25 squamous carcinomas, 4 cases (16%) were positive for MAP-2, 2 cases (8%) were positive for synaptophysin, 11 cases (44%) were positive for neuron-specific enolase, and none was positive for chromogranin. In conclusion, MAP-2 is a new sensitive and specific marker for the pulmonary tumors of neuroendocrine differentiation. We recommend that MAP-2 be added to immunohistochemical panels to separate non-neuroendocrine from neuroendocrine lung tumors.     

Differential distribution of the neuron-associated class III beta-tubulin in neuroendocrine lung tumors

OBJECTIVE: To study the immunoreactivity profile of the neuron-associated class III beta-tubulin isotype (beta III) in epithelial lung tumors. DESIGN: One hundred four formalin-fixed, paraffin-embedded primary and metastatic lung cancer specimens were immunostained with an anti-beta III mouse monoclonal antibody (TuJ1) and an anti-beta III affinity-purified rabbit antiserum. Paraffin sections from fetal, infantile, and adult nonneoplastic lung tissues were also examined. RESULTS: In the fetal airway epithelium, beta III staining is detected transiently in rare Kulchitsky-like cells from lung tissues corresponding to the pseudoglandular and canalicular but not the saccular or alveolar stages of development. beta III is absent in healthy, hyperplastic, metaplastic, and dysplastic airway epithelium of the adult lung. In contrast, beta III is highly expressed in small cell lung cancer, large cell neuroendocrine carcinoma, and in some non-small cell lung cancers, particularly adenocarcinomas. There is no correlation between expression of beta III and generic neuroendocrine markers, such as chromogranin A and/or synaptophysin, in pulmonary adenocarcinomas. Also, focal beta III staining is present in primary and metastatic adenocarcinomas (to the lung) originating in the colon, prostate, and ovary. beta III is expressed to a much lesser extent in atypical carcinoids and is rarely detectable in typical carcinoids and squamous cell carcinomas of the lung. The distribution of beta III in small cell lung cancer and adenocarcinoma metastases to regional lymph nodes and brain approaches 100% of tumor cells, which is substantially greater than in the primary tumors. CONCLUSIONS: In the context of neuroendocrine lung tumors, beta III immunoreactivity is a molecular signature of high-grade malignant neoplasms (small cell lung cancer and large cell neuroendocrine carcinoma) although its importance in atypical carcinoids must be evaluated further. In addition, beta III may be a useful diagnostic marker in distinguishing between small cell lung cancers and certain non-small cell lung cancers (poorly differentiated squamous cell carcinomas), especially in small biopsy specimens. To our knowledge, beta III is the only tumor biomarker that exhibits a substantially more widespread distribution in poorly differentiated than in better differentiated pulmonary neuroendocrine tumors. However, the significance of beta III phenotypes in non-small cell lung cancer, particularly adenocarcinoma, with respect to neuroendocrine differentiation and prognostic value, requires further evaluation.     

Incidence of latent infection of Epstein–Barr virus in lung cancers—an analysis of EBER1 expression in lung cancers by in situ hybridization

To evaluate the presence of Epstein–Barr virus (EBV) in lung cancers of Japanese patients, 81 lung cancers were examined using a highly sensitive in situ hybridization (ISH) method, employing an antisense oligonucleotide probe for EBV-encoded small nuclear RNA-1 (EBER). EBER1 expression was demonstrated in one poorly differentiated squamous cell carcinoma associated with marked lymphoid stroma (PDSCC-LS), two well differentiated adenocarcinomas, and two moderately differentiated squamous cell carcinomas, but was not detectable in other lung cancers, including small cell carcinomas. Unlike lymphoepithelioma-like undifferentiated carcinoma (LELC) of the lung, the PDSCC-LS consisted of poorly differentiated cells with distinct cell borders and nuclei with a coarse chromatin pattern and some prominent nucleoli. Most of the cancer cells expressed intense EBER1 signals. Although small to moderate numbers of cells positive for EBER1 were present in two adenocarcinomas and two squamous cell carcinomas, EBER1 signals varied in intensity and number in these four cases. Although polymerase chain reaction (PCR) and Southern blot hybridization with a ³²P-labelled probe internal to the primers were conducted to detect the EBV genome in 24 lung cancers, including five EBER1-positive cases, the genome was found to be positive in the five cases with EBER1-positive staining, including the PDSCC-LS, two adenocarcinomas and two squamous cell carcinomas, but not in the other cases. This study indicates that the morphological features of EBV-associated lung cancers are not restricted to the typical LELC type.     

Prognostic significance of anti-apoptosis proteins survivin and bcl-2 in non-small cell lung carcinomas: a clinicopathologic study of 102 cases.

Inhibitors of apoptosis, including bcl-2 and survivin (a novel gene encoding a unique apoptosis inhibitor), regulate cell proliferation by promoting cell survival. Although survivin has been detected in several human cancers, its prognostic significance and relationship to bcl-2 are not well characterized in lung cancer. Tissue sections from 102 non-small cell lung carcinomas (NSCLC) were immunostained using antibodies against survivin and bcl-2. Staining results were correlated with prognostic variables. Immunoreactivity for survivin and bcl-2 was observed in 53% and 21% of NSCLCs, respectively. Fifty-two percent of the 50 squamous cell carcinomas and 54% of the 52 adenocarcinomas expressed survivin. Survivin positivity correlated with tumor stage in squamous cell carcinoma. On univariate analysis, survivin expression correlated with decreased patient survival in NSCLC and in the subset of squamous cell carcinomas, but not in adenocarcinomas. On multivariate analysis, survivin was an independent predictor, along with distant metastasis and large tumor size. Eighteen percent of squamous cell carcinomas and 24% of adenocarcinomas expressed bcl-2. On univariate analysis, bcl-2 expression correlated with increased patient survival in NSCLC and in the subset of squamous cell carcinomas. An inverse correlation between the expression of survivin and bcl-2 was noted. Survivin immunoreactivity is an independent predictor of shortened survival in NSCLC, while bcl-2 protein expression correlated with prolonged patient survival. These findings indicate an inverse relationship between survivin and bcl-2 expression and suggest that these two inhibitors of apoptosis function through different pathways in the regulation of tumorigenesis in NSCLC.     

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.     

Neurotrophins and neurotrophin receptors in human lung cancer.

The expression of neurotrophins (NTs) and related high- and low-affinity receptors was studied in surgical samples of histologically diagnosed human tumors of the lower respiratory tract. The experiment was conducted with 30 non-small cell lung cancer specimens and in eight small cell lung cancer specimens by Western blot analysis and immunohistochemistry to assess expression and distribution of NT and NT receptor proteins in tissues examined. Immunoblots of homogenates from human tumors displayed binding of anti-nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and NT-3 antibodies as well as of anti-tyrosine-specific protein kinase (Trk) A, TrkB, and TrkC receptor antibodies, with similar migration characteristics than those displayed by human beta-NGF and proteins from rat brain. A specific immunoreactivity for NTs and NT receptors was demonstrated in vessel walls, stromal fibroblasts, immune cells, and sometimes within neoplastic cell bodies. Approximately 33% of bronchioloalveolar carcinomas exhibited a strong membrane NGF and TrkA immunoreactivity, whereas 46% adenocarcinomas expressed an intense TrkA immunoreactivity but a weak immunostaining for NGF within tumor cells. Moreover, squamous cell carcinomas developed an intense TrkA immunoreactivity only within stroma surrounding neoplastic cells. A faint BDNF and TrkB immunoreactivity was documented in adenocarcinomas, squamous cell carcinomas, and small cell lung cancers. NT-3 and its corresponding TrkC receptor were found in a small number of squamous cell carcinomas within large-size tumor cells. No expression of low-affinity p75 receptor protein was found in tumor cells. The detection of NTs and NT receptor proteins in tumors of the lower respiratory tract suggests that NTs may be involved in controlling growth and differentiation of human lung cancer and/or influencing tumor behavior.     

Bcl-2 protein and prognosis in patients with potentially curable non-small-cell lung cancer

The bcl-2 proto-oncogene functions as a cell death suppressor, and its expression prolongs cell survival by blocking apoptosis. Data available on the clinical relevance of bcl-2 protein expression in patients with non-small-cell lung cancer (NSCLC) are controversial. We analysed the role of bcl-2 protein expression on 6-year relapse-free survival in 229 patients with stage I-IIIa NSCLC (101 squamous cell carcinomas and 128 adenocarcinomas) subjected to surgery, with curative intent. Immunohistochemical analysis was performed on archival material by using a monoclonal antibody anti-bcl-2 (clone 124). Bcl-2 protein expression, which was detected in 22% of the cases, was significantly related to stage, histology and grading, and was an indicator of clinical outcome. The probability of relapse-free survival at 6 years was longer for patients with bcl-2-positive tumours (74%) than for those with bcl-2-negative tumours (57%) (P=0.02). This finding was mainly evident for the subgroups of patients with stage IIIa tumours (P=0.05), squamous cell carcinoma (P=0.03) or moderately/poorly differentiated tumours (P=0.02). However, multivariate analysis by Weibull’s regression model indicated that bcl-2 protein expression was not an independent prognostic risk factor in patients with curable NSCLC when the information provided by stage was available.     

An immunohistochemical study of lung carcinomas using a monoclonal antibody which specifically reacts to basal cells

Sixty-three primary lung carcinomas were examined immunohistochemically using a monoclonal antibody, KP8D4, which reacted specifically to basal cells in the lung. Seven of ten squamous cell carcinomas, four of 41 adenocarcinomas, two of five large cell carcinomas, and one adenosquamous carcinoma were reactive with KP8D4; however, four small cell carcinomas, one mucoepidermoid carcinoma, and one carcinoid tumor were all not reactive to this antibody. Four adenocarcinomas stained by KP8D4 were Clara cell type adenocarcinomas, and two of them also revealed reactivity to surfactant apoprotein in the same cells labeled with KP8D4. These results indicate that carcinomas positive to KP8D4, including adenocarcinomas at the lung periphery, expressed phenotypically the same protein which was specifically recognized in the basal cells, suggesting that the basal cells possessing a multipotent capability of differentiation are a possible candidate of progenitor cells of lung carcinomas, including peripheral type lung carcinomas.     

Ultrastructural and molecular heterogeneity in non-small cell lung carcinomas: study of 110 cases and review of the literature

The authors reviewed a series of 110 surgical specimens of primary non-small cell lung carcinomas from the Department of Pathology at the Hospital Clinic, University of Barcelona Medical School, between 1987 and 1997. The sample included 25 squamous cell carcinomas, 60 adenocarcinomas, 14 large cell carcinomas, and 11 neuroendocrine tumors. Electron microscopic subcellular characteristics of the lung cancer cells were studied to define the squamous, adenoid, or neuroendocrine differentiation in each tumor. An immunohistochemical study for Cyclin D1 was performed in 96 cases. In 71 cases (65%) the author found a single ultrastructural differentiation, and in 30 cases (27%) ultrastructural differentiation was double: 25 adenosquamous and 5 adeno-neuroendocrine. In 3 cases a triple adeno-squamous-neuroendocrine differentiation was found. There were no cases of squamous-neuroendocrine differentiation. In 6 cases no differentiation of any kind could be found. Cyclin D1 overexpression was found in 58% of all tumors. The positive expression rates in squamous cell carcinoma and adenocarcinoma were 72% and 62%, respectively. In purely adenoid-differentiated tumors there was a strong association between high Cyclin D1 overexpression and differentiation (p=.006). In bronchioloalveolar carcinoma the positivity rate was 70%; all were heavy expressers, compared with 25% of heavy expressers in adenocarcinomas as a whole (p<.005). In purely squamous tumors differentiated ultrastructurally no relationship was found between high Cyclin D1 expression and degree of differentiation (p=.08). Lung cancers are morphologically and molecularly heterogeneous, and certain molecular alterations are related to specific subcellular characteristics.     

CD44 expression is a feature of prostatic small cell carcinoma and distinguishes it from its mimickers

Small cell neuroendocrine carcinoma of the prostate is a rare variant of prostatic cancer that shares morphologic similarity with prostatic adenocarcinoma of Gleason 5 pattern. It has also been considered morphologically and immunohistochemically indistinguishable from small cell neuroendocrine carcinomas of other origins. CD44 is a cell-surface molecule proposed to identify cancer stem/progenitor cells in prostate cancer. We performed immunohistochemical study for CD44 expression in 11 cases of prostatic small cell neuroendocrine carcinoma and compared its patterns of expression with 73 cases of prostatic adenocarcinoma and 47 cases of small cell neuroendocrine carcinomas of other organs. Strong and diffuse membrane staining for CD44 was observed in 100% of the prostatic small cell neuroendocrine carcinomas. In conventional adenocarcinomas of the prostate, positive staining was only seen in rare, scattered tumor cells; and CD44 staining was negative in most of the small cell neuroendocrine carcinomas of nonprostate origin. The difference in CD44 expression between small cell neuroendocrine carcinomas of the prostate and those of other organs are statistically significant (P < .001). Our study demonstrates the utility of immunohistochemical staining for CD44 in distinguishing prostatic small cell neuroendocrine carcinoma from its mimickers including prostatic adenocarcinoma of Gleason 5 pattern and small cell neuroendocrine carcinomas of other organs. CD44 is the first marker that shows a high degree of tissue/organ specificity for small cell neuroendocrine carcinomas. Because CD44 is a putative marker of prostate cancer stem cells, the strong and diffuse expression of CD44 and the lack of expression of prostate luminal differentiation markers androgen receptor and prostatic specific antigen in prostatic small cell neuroendocrine carcinomas suggest that the tumor cells may retain cancer stem cell features.     

Laminin and type VII collagen distribution in different types of human lung carcinoma: correlation with expression of keratins 14, 16, 17 and 18

The expression patterns of basement membrane components and keratin intermediate filament proteins were studied in normal human bronchial epithelium and 56 lung carcinomas using monoclonal antibodies to laminin, type VII collagen and the individual keratins 14, 16, 17 and 18. In normal lung, laminin and type VII collagen were present between the epithelium and the lamina propria of bronchi and bronchioles. Keratin 14 was expressed in the basal cells, keratin 17 in the basal and some suprabasal cells and keratin 18 in the columnar cells of the bronchi and bronchioles. Keratin 16 was not present in normal bronchial epithelium. Laminin was found in all subtypes of lung carcinoma, but type VII collagen was present only in squamous cell carcinomas, where it showed a reduction in expression with decreasing differentiation. Type VII collagen was not identified in adenocarcinomas, small cell carcinomas or carcinoids. Antibodies to basal cell keratins 14 and 17 also displayed positivity only in squamous cell carcinomas, although no correlation with the degree of differentiation could be observed. Keratin 16 appeared to be a marker of the squamous phenotype, rather than of hyperproliferation. The keratin 18 marker for columnar epithelial cells showed a reaction pattern opposite to that of the basal cell keratins, being extensively present in adenocarcinomas, small cell carcinomas and carcinoids, with less expression in squamous cell carcinomas. This study shows a correlation between the presence of type VII collagen and the basal cell keratins 14 and 17, and a negative correlation between these components and keratin 18. These findings are likely to be useful in identifying lung cancer subtypes.     

Histopathology of sinonasal and lung cancers in nickel refinery workers

Histopathological diagnoses were compiled for 100 sinonasal cancers and 259 lung cancers in nickel refinery workers, including cases from Wales, Canada, and Norway. The sinonasal cancers comprised squamous cell carcinomas (48 percent), anaplastic and undifferentiated carcinomas (39 percent), adenocarcinomas (6 percent), transitional cell carcinomas (3 percent), and other malignant tumors (4 percent). The lung tumors comprised squamous cell carcinomas (67 percent), anaplastic, small cell, and oat cell carcinomas (15 percent), adenocarcinomas (8 percent), large cell carcinomas (3 percent), other malignant tumors (1 percent), and cancers not otherwise specified (6 percent). Possible selection bias in these data cannot be excluded, since the histological diagnoses represent 63 percent, 68 percent, and 100 percent of cases of sinonasal cancer and 24 percent, 47 percent, and 86 percent of cases of lung cancer in the Welsh, Canadian, and Norwegian workers. This study suggests that (a) the sinonasal cancers in nickel refinery workers conformed to the usual distribution of histological types observed in the general population (in contrast to the predilection for adenocarcinomas in wood workers), and (b) the lung cancers in nickel-refinery workers showed preponderance of squamous cell carcinomas and deficit of adenocarcinomas, compared to prevalent proportions of these neoplasms, possibly reflecting the paucity of women in the cohorts and temporal trends during the six decades in which the tumors were diagnosed.     

A 22-kd surface antigen detected by monoclonal antibody E 48 is exclusively expressed in stratified squamous and transitional epithelia.

After immunization of mice with viable cells of a metastasis of a laryngeal squamous cell carcinoma, a monoclonal antibody E 48 was obtained that detects an epitope present exclusively in squamous and transitional epithelium and their neoplastic counterparts. Immunoblotting revealed that E 48 recognizes a 22 kd molecule. Seventy-five of 76 squamous cell carcinomas from the head and neck, lung, cervix, and skin stained positively, whereas various adenocarcinomas from the colon, lung, and breast, and small cell lung carcinomas consistently stained negatively. The E 48 antigen, which is formaldehyde resistant, appears to be a reliable marker for differentiation of squamous cell carcinomas from adenocarcinoma, and small cell carcinomas.     

Utility of 123C3 monoclonal antibody against CD56 (NCAM) for the diagnosis of small cell carcinomas on paraffin sections

CD56 is immunohistochemically detectable in virtually all small cell carcinomas on frozen sections. The authors retrospectively tested the usefulness of the monoclonal antibody 123C3 against CD56 to differentiate pulmonary and extrapulmonary small cell carcinomas from nonneuroendocrine non—small cell carcinomas by paraffin-section immunohistochemistry after antigen retrieval. The study included 70 small cell carcinomas and 344 primary and metastatic nonneuroendocrine carcinomas of various primary sites. The staining results were compared with specific neuroendocrine markers (CD57, Chromogranin A, Synaptophysin). The monoclonal antibody 123C3 diffusely stained most small cell carcinomas with a strong membranous pattern (sensitivity: 0.99). The staining intensity was not diminished in areas with crush artifacts or after decalcification. The neuroendocrine markers had a combined sensitivity of only 0. 44 for small cell carcinomas. With regard to nonneuroendocrine carcinomas, the 123C3 antibody stained 7 of 28 ovarian carcinomas, 6 of 30 renal cell carcinomas, 2 of 10 endometrial carcinomas, two of three nonneuroendocrine large cell carcinomas of the lung, 1 of 38 adenocarcinomas, and 4 of 52 squamous cell carcinomas of the lung. Urothelial carcinomas, hepatocellular carcinomas, squamous carcinomas of the head/neck and cervix uteri, as well as adenocarcinomas of the breast, stomach, colon, pancreas, and prostate, showed no immunoreactivity for CD56. The specificities of 123C3 and the combined neuroendocrine markers for small cell carcinomas were 0. 94 and 0. 95, respectively. The authors conclude that monoclonal antibody 123C3 might be useful for the immunohistochemical differentiation of small cell carcinomas from nonneuroendocrine carcinomas on paraffin sections, especially in small and crushed biopsy specimens.