Sox10-positive sustentacular cells in neuroendocrine carcinoma of the lung

Cervical Small Cell Variant of Paraganglioma With Sarcomatous Transformation: Report of a Unique Case

We report a unique primary cervical neoplasm in a 44-yr-old woman which we believe, based on the morphology and immunophenotype, represents an extremely unusual small cell variant of paraganglioma. This represents the first report of a primary cervical paraganglioma. Following chemoradiation treatment, the tumor underwent malignant transformation into an S100 and SOX10 positive sarcoma, morphologically and immunohistochemically resembling a malignant peripheral nerve sheath tumor, which we believe represents a sarcoma derived from the sustentacular cells of the paraganglioma. Mutational analysis detected a nonsense mutation of NF1 gene in the sarcoma. This further supports the diagnosis as both somatic and germline NF1 mutations have been associated with paragangliomas and malignant peripheral nerve sheath tumors. Targeted RNA sequencing (ARCHER, expanded sarcoma panel) covering many known genes implicated in sarcoma development, did not reveal any other molecular alteration (fusion or internal tandem duplication).

RB1 gene mutations are a distinct predictive factor in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare cutaneous neuroendocrine carcinoma that tends to show local recurrence and metastasis. Typically, MCC is polyomavirus (MCPyV)-associated and cytokeratin 20 (CK20) positive. However, little is known about this tumor and its origins. Here, we aimed to determine the developmental origins of MCC and to identify prognostic clinicopathologic factors. Initial examinations revealed that CK20 and MCPyV expression (CK20+, MCPyV+ (60%); CK20+, MCPyV- (10%); CK20-, and MCPyV- (30%)) did not affect overall survival. With RB1 gene sequencing of FFPE specimens, which covered an entire exon, all RB1 mutation-positive cases showed positive regional lymph node and/or distant metastases (8/8 cases, 100%), whereas the frequency of the metastasis was statistically significantly lower in RB1 mutation-negative cases, (10/16 cases, 62%, P = 0.033). The results were also confirmed with immunohistochemistry, and either RB1 alterations, entire exon sequencing, or immunohistochemistry was associated with the metastasis (P = 0.007). RB1 alterations may be used to access the aggressive clinical course of MCC.

Morphologic Variants of Pancreatic Neuroendocrine Tumors: Clinicopathologic Analysis and Prognostic Stratification

Better prognostication/stratification of pancreatic neuroendocrine tumors (PanNETs) is needed. In this detailed morpheomic study of 163 resected PanNETs, 11 unusual variants, some of which were not previously recognized, and others scarcely documented in the literature, were identified, and their pathologic characteristics were further analyzed. By behavior and clinicopathologic associations, these variants could be grouped into three prognostically different categories. I. More aggressive (20%). Included in this group were the variants that in average showed higher grade and stage and adverse outcome including oncocytic, plasmacytoid, lipid-rich and previously unrecognized hepatoid variants, which often had a more diffuse/broad-band growth pattern, with some also displaying discohesiveness. They were characterized by abundant cytoplasm and often had prominent nucleoli (as seen in metabolically active cells), thus the provisional name "metabolic cell phenotype." Because of their diversion from classical neuroendocrine cytomorphology, these variants created challenges on original diagnostic workup, particularly hepatoid examples, which revealed Arginase 1/Hep Par-1 expression in 50%. II. Less aggressive (10%). These cases either showed signs of maturation, including nested growth, paraganglioid pattern (which was previously unrecognized), and organoid PanNETs such as "ductulo-insular" growth, or showed symplastic/degenerative changes, and despite their paradoxically disconcerting histology, were more benevolent in behavior. III. Undetermined. There were other variants including mammary tubulolobular-like, pseudoglandular, peliotic, and sclerotic PanNETs, which although diagnostically challenging, their biologic significance could not be determined because of rarity or heterogeneous characteristics. Prognostic associations: Features that were significantly different in the more aggressive group than the less aggressive group were median size (5.0 vs 1.6 cm, p < 0.001), percentage of pT3+T4 cases (72% vs 12%, p < 0.001), Ki67 index (5.3% vs 2.3%, p = 0.001), % G2 and G3 cases (77% vs 27%, p < 0.001), and rate of lymph node and distant metastasis (96% vs 27%, p < 0.001). In stepwise logistic regression model using the 3 established prognosticators of T stage, size, and grade along with morphology, only aggressive-morphology (metabolic cell phenotype) was found to be associated with metastatic behavior with an odds ratio of 5.9 with 95% confidence interval (C.I.) 1.688 to 22.945 and p value 0.007. In conclusion, PanNETs display various morphologic patterns that are not only challenging and important diagnostically but appear to have biologic significance. Tumors with more diffuse growth of cells with nucleoli and abundant cytoplasm and/or discohesion (oncocytic, hepatoid, lipid-rich, plasmacytoid PanNETs), provisionally termed "metabolic cell phenotype," show aggressive characteristics and are an independent determinant of adverse outcome and thus may require closer post-surgical follow-up, whereas variants with more degenerative or mature features (ductuloinsular, pleomorphic, paraganglioma-like) appear to be more benevolent despite their more atypical and worrisome morphology.

Immunohistochemical distinction of paragangliomas from epithelial neuroendocrine tumors-gangliocytic duodenal and cauda equina paragangliomas align with epithelial neuroendocrine tumors

Distinction of paraganglioma (PGL) from epithelial neuroendocrine tumors (NETs) can be difficult as they can mimic each other by nested architecture and expression of neuroendocrine markers. In this study, we examined differential diagnostic markers in 262 PGLs (142 adrenal pheochromocytomas and 120 extra-adrenal PGLs), 9 duodenal gangliocytic PGLs and 3 cauda equina PGLs, and 286 NETs (81 GI, 78 pancreatic, 42 thoracic, 37 medullary thyroid carcinomas, and 48 high-grade NETs including 32 small cell carcinomas of lung). While keratin expression was nearly uniform in NETs with the exception of few tumors, extensive keratin expression was seen in only one PGL (<1%) and focal expression in 5% PGLs. GATA3 was present in >90% of PGLs but only in 2% of NETs, usually focally. Tyrosine hydroxylase (TH) was expressed in >90% of adrenal, abdominal, and thoracic PGLs but only in 37% of head and neck PGLs, reflecting their variable catecholamine synthesis. Focal or occasional extensive TH-expression was detected in 10% of NETs. CDX2 was a helpful discriminator seen in 28% of pancreatic and most GI NETs but in no PGLs. SOX10 detected sustentacular cells in 85% of PGLs and 7% of NETs, whereas GFAP detected sustentacular cells mainly in PGLs of neck and was absent in NETs. Duodenal gangliocytic PGLs (n = 9) and all cauda equina PGLs (n = 3) expressed keratins, lacked GATA3, showed no or minimal TH expression as some NETs, and contained SOX10 and S100 protein-positive spindle cells negative for GFAP. Ganglion-like epithelioid cells were keratin-positive and negative for TH and SOX10 differing from true ganglion cells. We conclude that duodenal gangliocytic and cauda equina PGLs have a NET-like immunoprofile and differ from ordinary PGLs. NETs can be distinguished from PGLs by their expression of keratins and general lack of GATA3, TH, and GFAP-positive sustentacular cells, and sometimes by expression of CDX2 or TTF1.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

Immunohistochemistry in the diagnosis and classification of neuroendocrine neoplasms: what can brown do for you?

This review is based on a presentation given at the Hans Popper Hepatopathology Society companion meeting at the 2019 United States and Canadian Academy of Pathology Annual Meeting. It presents updates on the diagnosis and classification of neuroendocrine neoplasms, with an emphasis on the role of immunohistochemistry. Neuroendocrine neoplasms often present in liver biopsies as metastases of occult origin. Specific topics covered include 1. general features of neuroendocrine neoplasms, 2. general neuroendocrine marker immunohistochemistry, with discussion of the emerging marker INSM1, 3. non-small cell carcinoma with (occult) neuroendocrine differentiation, 4. the WHO Classification of neuroendocrine neoplasms, with discussion of the 2019 classification of gastroenteropancreatic neoplasms, 5. use of Ki-67 immunohistochemistry, 6. immunohistochemistry to assign site of origin in neuroendocrine metastasis of occult origin, 7. immunohistochemistry to distinguish well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma, 8. lesions frequently misdiagnosed as well-differentiated neuroendocrine tumor, and 9. required and recommended data elements for biopsies and resections with associated immunohistochemical stains. Next-generation immunohistochemistry, including lineage-restricted transcription factors (e.g., CDX2, islet 1, OTP, SATB2) and protein correlates of molecular genetic events (e.g., p53, Rb), is indispensable for the accurate diagnosis and classification of these neoplasms.

Clinical and Pathologic Characteristics of Pulmonary Carcinoid Tumors in Central and Peripheral Locations

Pulmonary carcinoid tumors occur in both central and peripheral locations, and some differences in clinico-pathological features have long been observed. We investigated a large number of resected carcinoid tumors with the aim to further define the characteristics of tumors from both locations. One hundred sixty-six resected carcinoid tumors of the lung were analyzed for a variety of clinical and pathologic features, including histology subtype, mitotic rate, Ki67 index, necrosis, invasive pattern, architectural pattern, cell morphology, sustentacular cells, neuroendocrine hyperplasia, and orthopedia homeobox protein (OTP) and TTF-1 immunohistochemical expressions. Unsupervised hierarchical cluster analysis suggested three clusters as the best solution using TTF-1 and OTP expression: TTF-1-positive and OTP-positive tumors as cluster 1, TTF-1-positive but OTP-negative as cluster 2, and TTF-1-negative and OTP-negative as cluster 3. Cluster 1 was characterized by peripheral location, presence of spindle cell component, presence of sustentacular cells, female predominance, and strong association with neuroendocrine hyperplasia. Cluster 2 was characterized by central location, polygonal cell morphology, acinar growth pattern in a subset of tumors, and only rare association with neuroendocrine hyperplasia. Cluster 3 consisted of more aggressive tumors with more heterogeneous pathologic features. Tumors showed polygonal cell morphology and acinar growth pattern. Occurrence of neuroendocrine hyperplasia was exceptional. Our study confirmed distinct characteristics of central and peripheral type carcinoid. An important difference was a strong association of the peripheral tumor with neuroendocrine hyperplasia while such an association in central tumors was negligible. The tumor location might be relevant for pathobiology of lung carcinoid tumors.

High-grade Neuroendocrine Carcinoma of the Lung With Carcinoid Morphology: A Study of 12 Cases

Twelve lung neuroendocrine tumors with morphologic features of carcinoid tumors but with mitotic count >10/2 mm are reported. There were 7 males and 5 females, with age ranging from 56 to 78 years. Four cases were from never-smokers. All tumors showed architectural and cytomorphologic features of carcinoid tumor, including organoid nesting, insular, trabecular, or acinar growth, and tumor cells with low nucleocytoplasmic ratio, abundant cytoplasm, ovoid to round nuclei, and salt and pepper chromatin. Angulated or confluent nesting, insular or lobular growth pattern was also seen. Nuclear irregularities and anisonucleosis were focally present. Mitotic count ranged from 11 to 61/2 mm. Punctate-type necrosis was present in 8 tumors. Anaplastic cytology, large infarct-type necrosis, desmoplasia, or marked inflammatory infiltrate was not found in any of the tumors. One tumor occurred in the background of diffuse idiopathic pulmonary neuroendocrine hyperplasia. All tumors were treated by resection, and all but 1 patient subsequently developed metastasis, and 7 died of the tumor. For metastatic tumors, 4 patients were treated by platinum-based chemotherapy with no apparent response, whereas 3 other patients were treated by combined capecitabine and temozolomide-novel chemotherapy for well-differentiated neuroendocrine tumor/carcinoid tumor-2 of them responded. This subset of tumor would be classified as large cell neuroendocrine carcinoma according to the current WHO classification scheme, but their clinical and pathologic features appear to have more in common with the carcinoid tumor group than large cell neuroendocrine carcinoma, therefore, identification of this subset may be relevant for further therapeutic management.

Examination of PHOX2B in adult neuroendocrine neoplasms reveals relatively frequent expression in phaeochromocytomas and paragangliomas

AIMS

Paired-like homeobox 2b (PHOX2B) is a transcription factor with expression outside of the central nervous system restricted to neurons and chromaffin cells of the autonomic nervous system. Germline mutations cause congenital central hypoventilation syndrome and predispose to neuroblastoma and Hirschsprung disease. Among paediatric small round cell tumours, PHOX2B is neuroblastoma-specific. Two studies of adult autonomic nervous system tumours (n = 62) produced conflicting results (all tumours stained in one; expression restricted to 40% of paragangliomas in the other). We examined PHOX2B expression in a large cohort of phaeochromocytomas and paragangliomas, as well as well-differentiated neuroendocrine tumours (WDNETs) and poorly differentiated neuroendocrine carcinomas (PDNECs).

METHODS AND RESULTS

Tissue microarrays (TMAs) were constructed from 609 tumours: 111 phaeochromocytomas, 146 paragangliomas, 250 WDNETs, and 102 PDNECs. PHOX2B immunohistochemistry was scored for extent (%) and intensity (0-3+), and an H-score (extent × intensity) was calculated. PHOX2B expression was seen in 32% of phaeochromocytomas and in 47% of paragangliomas. Mean/median H-scores for these tumours were in the 30-55 range (i.e. weak to moderate staining). No WDNETs and only 7% of PDNECs stained, the latter often strongly. In a representative cohort of corresponding whole sections (n = 55), the results in WDNETs and PDNECs were unchanged, whereas half of the phaeochromocytomas/paragangliomas that were negative on TMAs became focally, weakly positive.

CONCLUSIONS

We found frequent, weak to moderate PHOX2B expression in phaeochromocytomas/paragangliomas and no expression in WDNETs, which could be diagnostically useful in the distinction of these tumours. Expression in a minority of PDNECs probably reflects the transcription factor lineage infidelity that is characteristic of this tumour class.

Sox10 expression in ovarian epithelial tumors is associated with poor overall survival

Sox10 is a transcription factor regulating the development of several cell lineages and is involved in tumor development. However, the clinicopathological relevance of Sox10 expression in ovarian cancer has not been examined. We assessed expression of Sox10 in ovarian epithelial tumors by immunohistochemistry and assessed its prognostic value by analyzing the correlation between its expression and clinicopathological factors. We used tissue microarrays including 244 ovarian epithelial tumors. Sox10 staining was found in the cytoplasm or nucleus of tumor cells. Malignant serous, mucinous, and endometrioid tumors were significantly more likely to express Sox10 than benign and borderline tumors. Expression patterns in adenocarcinomas were different for histologic subtypes: nuclear Sox10 staining was common in clear-cell adenocarcinomas and serous adenocarcinomas, whereas all cases of mucinous and endometrioid tumors were negative for nuclear staining. Nuclear Sox10 staining was also associated with chemoresistance and shorter overall survival in ovarian adenocarcinomas, notably in high-grade serous adenocarcinoma. Sox10 is expressed in many ovarian carcinomas, suggesting that it might be involved in oncogenesis of ovarian carcinoma. Expression pattern of Sox10 differs between histological subtypes. Nuclear Sox10 expression is an independent indicator of poor prognosis in ovarian adenocarcinomas, notably in high-grade serous adenocarcinomas.

A Newly Developed Mouse Monoclonal SOX10 Antibody Is a Highly Sensitive and Specific Marker for Malignant Melanoma, Including Spindle Cell and Desmoplastic Melanomas

Context

Recent immunohistochemical studies have demonstrated Sry-related HMG-Box gene 10 (SOX10) expression in malignant melanomas, malignant peripheral nerve sheath tumors, a subset of breast carcinomas, and gliomas. SOX10 has shown important clinical utility in its ability to detect desmoplastic and spindle cell melanomas. To date, most publications have employed a research use–only goat polyclonal SOX10 antibody for immunohistochemical staining.

Objective

To describe the development of a new mouse monoclonal SOX10 antibody (BC34) and evaluate its immunohistochemical staining profile in a wide range of normal and neoplastic tissues, with an emphasis on melanoma.

Design

SOX10 antibody was optimized for staining using a polymer detection system and visualization with diaminobenzidine.

Results

In normal tissues, SOX10 was expressed in skin melanocytes and eccrine cells, breast myoepithelial and lobular epithelial cells, salivary gland myoepithelial cells, peripheral nerve Schwann cells, and central nervous system glial cells. SOX10 was expressed in 238 of 257 melanomas (92.6%), including 50 of 51 of both spindle cell and desmoplastic melanomas (98%). SOX10 was expressed in 100% of nevi (20 of 20) and schwannomas (28 of 28). In other neoplasms, SOX10 was expressed in 18 of 109 invasive ductal breast carcinomas (16.5%). All other carcinomas were negative for SOX10. SOX10 was identified in 25 of 52 central nervous system neoplasms, primarily in astrocytomas (22 of 41; 53.7%), and in 4 of 99 various sarcomas examined (4.0%).

Conclusions

The newly developed mouse monoclonal SOX10 antibody BC34 is highly sensitive and specific for malignant melanoma, including desmoplastic and spindle cell variants, and appears highly suitable for clinical use.

Paragangliomas: update on differential diagnostic considerations, composite tumors, and recent genetic developments

Recent developments in molecular genetics have expanded the spectrum of disorders associated with pheochromocytomas (PCCs) and extra-adrenal paragangliomas (PGLs) and have increased the roles of pathologists in helping to guide patient care. At least 30% of these tumors are now known to be hereditary, and germline mutations of at least 10 genes are known to cause the tumors to develop. Genotype-phenotype correlations have been identified, including differences in tumor distribution, catecholamine production, and risk of metastasis, and types of tumors not previously associated with PCC/PGL are now considered in the spectrum of hereditary disease. Important new findings are that mutations of succinate dehydrogenase genes SDHA, SDHB, SDHC, SDHD, and SDHAF2 (collectively "SDHx") are responsible for a large percentage of hereditary PCC/PGL and that SDHB mutations are strongly correlated with extra-adrenal tumor location, metastasis, and poor prognosis. Further, gastrointestinal stromal tumors and renal tumors are now associated with SDHx mutations. A PCC or PGL caused by any of the hereditary susceptibility genes can present as a solitary, apparently sporadic, tumor, and substantial numbers of patients presenting with apparently sporadic tumors harbor occult germline mutations of susceptibility genes. Current roles of pathologists are differential diagnosis of primary tumors and metastases, identification of clues to occult hereditary disease, and triaging of patients for optimal genetic testing by immunohistochemical staining of tumor tissue for the loss of SDHB and SDHA protein. Diagnostic pitfalls are posed by morphological variants of PCC/PGL, unusual anatomic sites of occurrence, and coexisting neuroendocrine tumors of other types in some hereditary syndromes. These pitfalls can be avoided by judicious use of appropriate immunohistochemical stains. Aside from loss of staining for SDHB, criteria for predicting risk of metastasis are still controversial, and "malignancy" is diagnosed only after metastases have occurred. All PCCs/PGLs are considered to pose some risk of metastasis, and long-term follow-up is advised.

Newly Available Antibodies With Practical Applications in Surgical Pathology

Selected antibodies that have become available in recent years and have applications in diagnostic pathology are discussed. They include antibodies that are organ-related, provide information on cellular differentiation or histogenetic type, have predictive value in tumors, and highlight infective agents. PAX8 (paired box gene 8) is a marker expressed in the lower female genital tract, thyroid, and kidney and their tumors. Napsin A is expressed in the lung and kidney and is an alternative marker for pulmonary adenocarcinoma. Arginase A is a sensitive and specific marker for liver tumors. ERG (Ets-related gene) is an excellent marker for endothelium and vascular tumors as well as prostatic cancer (about 50% of cases). SOX10 (SRY-related HMG box) is expressed predominantly in melanocytic and Schwann cells and the corresponding tumors. DOG1 (discovered on GIST 1) is an excellent marker for gastrointestinal stromal tumor (GIST) and acinic cell carcinoma. OCT3/4 is a pan–germ cell tumor marker, except yolk sac tumor. SALL4 is positive in various types of germ cell tumors, including yolk sac tumor. MUC4 (mucin-related antigen 4) is a sensitive and specific marker for low-grade fibromyxoid sarcoma. Langerin is a specific marker for Langerhans cells and their tumors. SOX11 is a sensitive marker for mantle cell lymphoma. New generation antibodies against anaplastic lymphoma kinase (ALK) are required to reliably demonstrate ALK gene translocation in pulmonary carcinomas. Lack of expression of succinate dehydrogenase B is seen in paragangliomas of the hereditary form and in the pediatric type of GIST. Antibodies against Trepenoma pallidum can facilitate the diagnosis of syphilis, whereas those against SV40 (simian virus 40) are helpful for diagnosis of BK virus infection and progressive multifocal leukoencephalopathy.

A study of gata3 and phox2b expression in tumors of the autonomic nervous system

Autonomic neurons and chromaffin cells, which constitute the autonomic nervous system, are derived from a common progenitor from the neural crest, and its development is controlled by a network of transcription factors, including the master regulator, Phox2b, and its downstream, Gata3. Anti-Phox2b and anti-Gata3 antibodies were applied to a total of 77 autonomic nervous system tumors, including 35 paragangliomas, 21 pheochromocytomas, 9 neuroblastomas, 4 ganglioneuroblastomas, and 8 ganglioneuromas, as well as their potential morphologic mimics, including tumors of the small round cell tumor group, neuroendocrine carcinomas of lung and gastrointestinal tract (carcinoid tumors/neuroendocrine tumors, large cell neuroendocrine carcinomas, and small cell carcinomas), Merkel cell carcinomas, benign and malignant tumors of thyroid, parathyroid, and adrenal cortex, and malignant melanomas. A variety of nonendocrine/neuroendocrine carcinomas were also studied. Gata3 expression was seen in 89% of paragangliomas, 95% of pheochromocytomas, and all neuroblastomas, ganglioneuroblastomas, and ganglioneuromas, as well as in all parathyroid tumors, a majority of urothelial and mammary carcinomas, and a subset of squamous cell carcinomas, but all other tumors were negative. Phox2b expression was seen in all neuroblastomas, ganglioneuroblastomas, and ganglioneuromas and in 40% of paragangliomas, but pheochromocytomas and all other tumors were negative. Gata3 is a highly reliable marker for paragangliomas, pheochromocytomas, and neuroblastic tumors to distinguish from their simulators. This is an additional utility for this marker, which is used for the diagnosis of urothelial and mammary carcinomas. Phox2b is also highly specific, but its low sensitivity to paragangliomas and pheochromocytomas would limit the utility only to neuroblastic tumors.

Clinicopathological and immunohistochemical analysis of spindle-cell carcinoid tumour of the lung

AIMS

To analyse the clinicopathological features and immunohistchemical profile of spindle-cell carcinoid tumours (SCCT) of the lung.

METHODS AND RESULTS

Using a cut-off value of ≥ 50% spindle cells for defining SCCT, 13 were indentified among 80 consecutively resected carcinoid cases. SCCTs are asymptomatic and are peripherally located, well-demarcated tumours. Tumour cells were composed of elongated spindle cells, with scant to moderate amounts of cytoplasm and uniform nuclei with fine granular chromatin. Immunohistochemical analysis revealed that all 13 cases were positive for three neuroendocrine markers (chromogranin A, synaptophysin and CD56). Four tumours (30.7%) were positive for broad-spectrum cytokeratin (CK) and nine tumours (69.2%) were positive for thyroid transcription factor 1. All epithelial components were negative for vimentin, but 12 tumours (92.3%) were positive for stellate-shaped cells (so-called sustentacular cells).

CONCLUSIONS

SCCTs are clinically asymptomatic, peripherally located, well-demarcated tumours, and patients with SCCTs have a favourable outcome. The immunoreactivity pattern of SCCT (low reactivity of broad-spectrum CK and reactivity for vimentin in intratumoral sustentacular cells) might result in a misdiagnosis of SCCT as mesenchymal tumour; therefore, pathologists need to be familiar with this pattern.