Neuroendocrine carcinoma of skin with simultaneous cytokeratin expression

Characterization of a Merkel Cell Polyomavirus-Positive Merkel Cell Carcinoma Cell Line CVG-1

Merkel cell polyomavirus (MCV) plays a causal role in ∼80% of Merkel cell carcinomas (MCC). MCV is clonally integrated into the MCC tumor genome, which results in persistent expression of large T (LT) and small T (sT) antigen oncoproteins encoded by the early locus. In MCV-positive MCC tumors, LT is truncated by premature stop codons or deletions that lead to loss of the C-terminal origin binding (OBD) and helicase domains important for replication. The N-terminal Rb binding domain remains intact. MCV-positive cell lines derived from MCC explants have been valuable tools to study the molecular mechanism of MCV-induced Merkel cell carcinogenesis. Although all cell lines have integrated MCV and express truncated LT antigens, the molecular sizes of the LT proteins differ between cell lines. The copy number of integrated viral genome also varies across cell lines, leading to significantly different levels of viral protein expression. Nevertheless, these cell lines share phenotypic similarities in cell morphology, growth characteristics, and neuroendocrine marker expression. Several low-passage MCV-positive MCC cell lines have been established since the identification of MCV. We describe a new MCV-positive MCV cell line, CVG-1, with features distinct from previously reported cell lines. CVG-1 tumor cells grow in more discohesive clusters in loose round cell suspension, and individual cells show dramatic size heterogeneity. It is the first cell line to encode an MCV sT polymorphism resulting in a unique leucine (L) to proline (P) substitution mutation at amino acid 144. CVG-1 possesses a LT truncation pattern near identical to that of MKL-1 cells differing by the last two C-terminal amino acids and also shows an LT protein expression level similar to MKL-1. Viral T antigen knockdown reveals that, like other MCV-positive MCC cell lines, CVG-1 requires T antigen expression for cell proliferation.

Combined Merkel Cell Carcinoma and Atypical Fibroxanthoma

Background:

Although there are reports of squamous cell carcinoma arising within and adjacent to Merkel cell carcinoma, and one report of an atypical fibroxanthoma-like tumor arising in an irradiated recurrent Merkel cell carcinoma, there have previously been no reports of an immunohistochemically verified atypical fibroxanthoma occurring in conjunction with a Merkel cell carcinoma.

Objective:

We report on a neoplasm with distinct features of both Merkel cell carcinoma and atypical fibroxanthoma.

Methods:

Histologic and immunohistochemical evaluations were performed.

Results:

Our results verify the finding of a combined Merkel cell carcinoma and atypical fibroxanthoma.

Conclusion:

This case is an interesting and unusual combination of tumors. The origin of the Merkel cell carcinoma is revisited. Debated origins include neuroendocrine, epithelial, and pleuripotent stem cell.

A comprehensive review of the treatment of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an uncommon but malignant cutaneous neuroendocrine carcinoma with a high incidence of local recurrence, regional lymph node metastases, and subsequent distant metastases. The etiology of MCC remains unknown. It usually occurs in sun-exposed areas in elderly people, many of whom have a history of other synchronous or metachronous sun-associated skin lesions. The outcome for most patients with MCC is generally poor. Surgery is the mainstay of treatment. The role of adjuvant therapy has been debated. However, data from recent development support a multimodality approach, including surgical excision of primary tumor with adequate margins and sentinel lymph node dissection followed by postoperative radiotherapy in most cases, as current choice of practice with better locoregional control and disease-free survival. Patients with regional nodal involvement or advanced disease should undergo nodal dissection followed by adjuvant radiotherapy and, perhaps, systemic platinum-based chemotherapy in most cases.

Cisplatin-based chemotherapy for merkel cell carcinoma of the skin

PURPOSE

Merkel cell carcinoma (MCC), a rare tumor of the skin with aggressive behavior, is usually fatal when advanced disease is present. The role of chemotherapy (CT) in the treatment of patients with MCC is unclear.

METHODS

Over 15 years, 9 patients with locally advanced or metastatic disease were treated with carboplatin (CBDCA) (300 mg/m(2) of AUC 5 on Day 1) and etoposide (VP-16) (100 mg/m(2) on Days 1-3) every 3 weeks. As second-line CT, cisplatin (CDDP) (60-100 mg/m(2)), ifosfamide (IFO) (3-5 g/m(2)) and epirubicin (EPI) (30-50 mg/m(2)) were utilized.

RESULTS

Of the 3 patients who received adjuvant therapy, one achieved complete response after 108+ months with second-line chemotherapy and radiotherapy, despite a brief relapse; 2 patients remain disease-free after 84+ and 108+ months. Of the 6 patients with locally advanced or metastatic disease who were treated with first-line chemotherapy, one (16.6 percent) achieved a complete response and 3 (50 percent) achieved partial response, for an overall response rate of 66.6 percent. Two patients (one with complete and one with partial response) received subsequent radiotherapy, following which complete response was achieved. Of the 2 complete responders, one patient remains disease-free after 56+ months. The median overall survival from the time of initial diagnosis for the whole group was 56 months (range 15-114 months); the median overall survival from the initiation of chemotherapy was 18 months (range 6-108+). Local recurrences and soft tissue metastases responded better than visceral metastases. Patients with partial response and no response had rapid disease progression and fatality, despite second-line chemotherapy and/or radiotherapy.

CONCLUSION

MCC appears to be chemosensitive but can progress rapidly with fatal outcomes. Although the rarity of these tumors precludes randomized trials, a common treatment plan should be utilized by those treating MCC. This may allow some conclusions regarding the optimum treatment of patients with MCC to be drawn in the future.

Combined Merkel Cell Carcinoma and Atypical Fibroxanthoma

BACKGROUND

Although there are reports of squamous cell carcinoma arising within and adjacent to Merkel cell carcinoma, and one report of an atypical fibroxanthoma-like tumor arising in an irradiated recurrent Merkel cell carcinoma, there have previously been no reports of an immunohistochemically verified atypical fibroxanthoma occurring in conjunction with a Merkel cell carcinoma.

OBJECTIVE

We report on a neoplasm with distinct features of both Merkel cell carcinoma and atypical fibroxanthoma.

METHODS

Histologic and immunohistochemical evaluations were performed.

RESULTS

Our results verify the finding of a combined Merkel cell carcinoma and atypical fibroxanthoma.

CONCLUSION

This case is an interesting and unusual combination of tumors. The origin of the Merkel cell carcinoma is revisited. Debated origins include neuroendocrine, epithelial, and pleuripotent stem cell.

Insulin-like growth factor-1 increases intracellular calcium concentration in human primary neuroendocrine pancreatic tumor cells and a pancreatic neuroendocrine tumor cell line (BON-1) via R-type Ca2+ channels and regulates chromogranin a secretion in BON-1 cells

Insulin-like growth factor 1 (IGF-1) is a potent mitogenic and secretory factor that acts on voltage operated Ca(2+) channels (VOCCs). VOCCs are categorized into L-type channels (Ca(V)1.1-1.4), P/Q-type channels (Ca(V)2.1), N-type channels (Ca(V)2.2), R-type channels (Ca(V)2.3), and T-type channels (Ca(V)3.1-3.3). Aside from regulating membrane excitability, VOCCs influence chromogranin A (CgA) secretion in neuroendocrine tumor (NET) cells. It is not known, whether VOCCs play a role in the IGF-1-dependent regulation of CgA secretion in NET cells. We therefore studied the effects of IGF-1 on individual VOCC subtypes and characterized their role in mediating IGF-1-dependent regulation of CgA secretion in NET cells. Using specific modulators of VOCC subtypes, we identified the functional expression of L-, N-, P/Q- and R-type channels in primary as well as permanent models of NET. The IGF-1-induced intracellular Ca(2+) increase in NET cells was mainly due to the activation of R-type channel activity. The effects on intracellular calcium, observed in whole-cell patch-clamp recordings and fluorescence imaging, were partially blocked by the specific R-type channel blocker SNX-482 and antisense oligonucleotides against the alpha(1) subunit of this channel. IGF-1 potently induced CgA secretion. The effect of IGF-1 was reduced by both, inhibition of R-type channel activity and a reduction of R-type channel expression using antisense oligonucleotides. Since R-type channels exist in NET cells and couple to both, IGF-1 receptor signaling as well as CgA secretion, pharmacological interference with R-type channels may represent a new therapeutic option by blocking Ca(2+) signaling thereby abrogating IGF-1-dependent hypersecretion in NET disease.

Expression of alpha subunit of guanine nucleotide-binding protein Go in Merkel cell carcinoma

The alpha subunit of guanine nucleotide-binding protein Go (Go alpha), which was initially isolated from bovine brain, interacts with muscarinic cholinergic receptors and regulates neuronal calcium channels. Go alpha is known to be localized in neural tissues, some endocrine cells, and neuroendocrine tumors. We have immunohistochemically investigated the expression of Go alpha in 4 cases of Merkel cell carcinoma using the method of microwave treatment. In all cases of Merkel cell carcinoma, Go alpha was consistently detected on the plasma membrane and cytoplasm of the tumor cells. Nerve fibers in the skin were also positive for Go alpha, but other epidermal or dermal components such as keratinocytes, melanocytes, fibroblasts, or lymphoid cells were negative. Tumor cells of squamous cell carcinoma, cutaneous lymphoma, sweat gland carcinoma, and malignant melanoma were negative for Go alpha. The present study indicates that Go alpha may be a useful immunohistochemical marker of Merkel cell carcinoma.

Establishment and characterization of two Merkel cell tumor cultures

Two Merkel cell tumor cultures (MC-MA1, MC-MA2) have been established from metastases of typical Merkel cell tumors. The mestastases in vivo were characterized by co-expression of cytokeratins 8, 18, 19, 20 and neurofilaments, presence of intermediate filament whirls, expression of synaptophysin, neuron-specific enolase, and chromogranin A, rare and weak immunostaining for plakoglobin but absence of cadherins and desmoplakins. Both cultures grow, using supplemented RPMI medium on human irradiated fibroblast feeder layers, as loosely arranged floating small aggregates. Their karyotypes are mostly hyperdiploid. The mean doubling times were about 84 h in the first 8 months and later increased. Ultrastructural and immunoelectron microscopic studies of the Merkel cell tumor cells in vitro (MC-MA1, MC-MA2) revealed sparse membrane-bound neuroendocrine granules and typical IFs that were partly arranged in paranuclear whirls and were labeled by antibodies against cytokeratins and neurofilaments. In immunocytochemical studies using antibodies to cytokeratins 8, 18, 19, and 20 and neurofilament protein NF-L, Merkel cell tumor cells in vitro showed a uniform staining appearing as paranuclear whirls and cytoplasmic fibrils as well. Double-labeling experiments showed a co-localization of both intermediate filament types in most cells. Biochemically we found cytokeratins 8, 18, 19, and 20, and NF-L in tumor cells in vitro. Immunocytochemical staining was negative for desmoplakins, various cadherins, and cell adhesion molecules, whereas plakoglobin was only rarely detectable in some Merkel cell tumor cells in vitro. By immunoluminometric assay chromogranin A was detected in cell homogenates and culture supernatants as well. Immunocytochemically, synaptophysin and neuron-specific enolase were detectable additionally in some of the cells. These established cell cultures will allow further studies devoted to the biology, differentiation, and hormone secretion of Merkel cell tumors that may also increase our knowledge about normal Merkel cells.

The Merkel cell and associated neoplasms in the eyelids and periocular region

Merkel cells are clear oval cells in the epidermis and outer root sheaths of hair follicles, which are probably of epithelial origin, share ultrastructural features with neuroendocrine cells, and are found in association with touch receptors. In the eyelid, they occur singly in the epidermis and external root sheaths of hairs and eyelashes, and in specialized touch spots alternating with eyelashes. Their typical electron microscopical and antigenic features include dense-core granules, intranuclear rodlets, spinous processes, and a positive reaction for specific cytokeratins, epithelial membrane antigen, neuron-specific enolase, chromogranin and synaptophysin. Merkel cell carcinoma probably develops from precursor cells which give rise to keratinocytes and Merkel cells, and nearly one out of ten Merkel cell carcinomas occur in the eyelid and periocular region. They tend to be bulging lesions near the lid margin of elderly patients, reddish in color, and erythematous with telangiectatic vessels. The diagnosis is based on the frequent presence of neurofilaments and paranuclear aggregates of intermediate filaments in addition to features typical of normal Merkel cells. The tumor often mimics lymphoma or undifferentiated carcinoma and frequently invades lymphatic vessels. One third of Merkel cell carcinomas recur, almost two thirds give rise to regional node metastases, and up to one half metastasize widely and result in death. Initial treatment should be prompt and aggressive, with wide resection and routine postoperative irradiation. Although metastatic lesions often respond to radiation therapy and cytostatic drugs, these treatments are mainly of palliative value.

Neuroendocrine (Merkel-cell) carcinoma of the skin: immunocytochemical and cytomorphologic analysis on fine-needle aspirates

Cytomorphologic and immunocytochemical characteristics of tumor cells from fine-needle aspirates of four neuroendocrine (Merkel-cell) carcinomas of the skin are described. All aspirates were cellular with dispersed small to medium sized tumor cells with scanty cytoplasm. Many mitoses were observed. Careful scrutiny revealed a tendency of the tumor cells to form microacinar and pseudorosette formations as well as small clusters of molding cells. Immunocytochemical analysis of cytospin preparations showed a peculiar dot-like cytokeratin positivity, while neuron-specific enolase staining was more diffuse. A weak S-100 positivity was observed. This staining pattern is highly suggestive of Merkel-cell tumor. It can thus be concluded that immunocytochemical analysis in conjunction with cytomorphology on fine-needle aspirates will allow the identification of neuroendocrine carcinoma of the skin and its differentiation from other small-cell neoplasias of the skin.

Neuroendocrine carcinoma (Merkel cell tumor?) presenting as a subcutaneous tumor. An ultrastructural and immunohistochemical study of three cases

The clinical and pathological features of three unusual soft tissue tumors are presented. They occurred in the groin of elderly patients in the subcutaneous tissue. In Case 1, the inguino-crural tumor coexisted with a second mass in the pelvis. The tumors had a tendency to recur locally and to invade the regional lymph nodes. Metastatic dissemination of the disease resulted in the death of the patient in Case 3. Histologically, the tumors appeared composed of small round cells with scanty cytoplasms, arranged in diffuse, poorly cohesive or solid sheets. In places, a trabecular pattern was noted. Mitotic figures were numerous. Some cells exhibited argyrophil granules. The ultrastructural study revealed compact whorls of intermediate filaments and neurosecretory granules. All three cases displayed a paranuclear dot-like positive reaction with antibodies to cytokeratins and neurofilaments. A diffuse cytoplasmic immunostaining for neuron-specific enolase was present in Cases 1 and 2. Protein S-100, vimentin and leucocyte common antigen could not be demonstrated. All these characteristics, except for the subcutaneous location, are shared with neuroendocrine (Merkel cell) tumors of the skin.

Neuroendocrine (Merkel cell) carcinoma of the skin. Its natural history, diagnosis, and treatment

Over 400 cases of neuroendocrine (Merkel cell) carcinoma of the skin (NCS) have been reported. This tumor continues to pose problems in diagnosis and effective treatment for physicians unfamiliar with its biological characteristics. Reported here are five additional cases of NCS and the literature for this rare neoplasm is comprehensively reviewed. An early and accurate diagnosis is made possible by combining clinical presentation with results of histologic study, immunoperoxidase staining for neuron-specific enolase (NSE), epithelial membrane antigen (EMA), cytokeratins, and electron microscopy. NCS is an aggressive tumor. Depending on the length of follow-up, up to 40% of tumors locally recur, 55% develop regional nodal metastases, and 36% undergo distant metastasis. Survival is sex, but not age, dependent, with an overall 2-year survival rate of 72% (males 58% vs. females 79%). No standard procedure for initial and/or follow-up treatment for NCS exists. The authors recommend that NCS be treated, whenever possible, using the same rationale as applied for the treatment of squamous cell carcinoma of the skin.

Epidermotropic primary neuroendocrine (Merkel cell) carcinoma of the skin with Pautrier-like microabscesses. Report of three cases and review of the literature

Three cases of primary cutaneous neuroendocrine carcinoma involving the face are reported. In the first patient the tumor developed in the scar of a previously excised basal cell carcinoma of the nose, recurred locally, and metastasized to a regional lymph node 2 1/2 years after initial treatment. In the second and third patients the tumors were located on the forehead and were removed with a wide excision. In the second patient the tumor metastasized to regional lymph nodes 1 month after treatment. Light microscopic examination in all patients showed an undifferentiated, small cell, dermal tumor with prominent epidermotropism, forming Pautrier-like microabscesses. Immunohistochemical staining for neuron-specific enolase was positive, and ultrastructural examination revealed numerous cytoplasmic neurosecretory granules and paranuclear aggregates of intermediate-sized filaments. The literature concerning epidermal involvement by primary neuroendocrine carcinoma of the skin is reviewed; the relation with basal cell carcinoma and treatment are discussed.

Merkel cell tumor coexpressing cytokeratin and neurofilament proteins

Whorled filaments 10 nm in width were identified by anti-intermediate filaments antibodies in a Merkel cell tumor from a 52-year-old man. Immunohistochemical tests revealed that the tumor was stained with anti-keratin antibody and antibodies against the 68-kd and 200-kd subunits of neurofilament proteins but not antibody against the 150-kd subunit. This is the first reported case of Merkel cell tumor expressing a 200-kd subunit of neurofilament proteins.

Cytokeratin and laminin immunostaining in the diagnosis of cutaneous neuro-endocrine (Merkel cell) tumours

Nine cutaneous neuro-endocrine tumours have been immunostained with monoclonal antibodies to low molecular weight cytokeratin (CAM 5.2) and neurofilament. Polyclonal antisera to neurone-specific enolase, calcitonin and laminin were also used. All nine cases showed paranuclear, dot-like positive staining with CAM 5.2 and diffuse cytoplasmic staining for neurone-specific enolase. Neurofilament and calcitonin immunoreactivity could not be demonstrated. All tumours were negative for laminin immunoreactivity. The limitations of staining for neurone-specific enolase are discussed and the value of CAM 5.2 in the differential diagnosis of cutaneous neuro-endocrine tumours is emphasized. The histogenetic implications of the absence of laminin staining are considered.

The use of antikeratin antibodies in the immunohistochemical distinction between neuroendocrine (Merkel cell) carcinoma of the skin, lymphoma, and oat cell carcinoma

Paraffin sections of formalin-fixed tumor samples from 26 patients with neuroendocrine (Merkel cell) carcinoma of the skin (NECS) were studied immunohistochemically with three monoclonal antibodies to low molecular weight keratin (MAB-K) and with antibodies to leukocyte common antigen (LCA), neurofilament (NF), neuron-specific enolase (NSE), S100 protein (S100), and chromogranin (CGN), to investigate the relative diagnostic value of these antibodies. Samples from 20 lymphomas, 10 non-oat cell undifferentiated carcinomas, 10 oat cell carcinomas, and 10 melanomas served as controls. Keratin was found in 25 of the 26 NECS and in all undifferentiated and oat cell carcinomas. A ball-like immunostaining for keratins, resembling an inclusion body was seen only in cases of NECS and some carcinoids. Neurofilament, NSE, and CGN were expressed by fewer NECS than was keratin and all NECS were negative for LCA and S100. None of the lymphomas and melanomas contained detectable keratin, NF, NSE, or CGN. Only the lymphomas stained with LCA. Only the melanomas were S100-positive. It is concluded that keratin is the most useful single discriminating marker in the separation of neuroendocrine (Merkel cell) carcinoma of the skin from lymphoma, melanoma and, when the characteristic inclusion-like pattern is seen, from metastatic oat cell carcinoma.

Neuroendocrine carcinoma of the skin: an immunohistochemical study of tumor markers and neuroendocrine products

Fifteen neuroendocrine carcinomas of the skin (Merkel cell tumors) were stained within the constraints of tissue availability by the Grimelius method and immunohistochemically for keratin, neuron-specific enolase (NSE), carcinoembryonic antigen (CEA), S-100, common leukocyte antigen (CLA), met-enkephalin, bombesin, calcitonin, ACTH, gastrin, and somatostatin. Focal argyrophilia was present in 5 of 12 tumors. All tumors tested demonstrated immunoreactivity for NSE and 5 tumors were positive for keratin. One tumors appeared to demonstrate focal ACTH-like immunoreactivity, but otherwise no immunoreactivity for the above mentioned polypeptide hormones was noted in 11 completely studied tumors. One tumor contained histologically obvious areas of squamous differentiation in addition to areas of Merkel cell tumor. In various tumors, keratin immunoreactivity was present either in areas of histologically obvious squamous differentiation, in randomly scattered single cells not histologically identifiable as squamous, or in a paranuclear dot-like distribution. Immunoreactivity for CEA, S-100 and CLA was not present in any tumors. The lack of met-enkephalin and the presence of squamous differentiation in these tumors indicates multidirectional differentiation in a fashion not phenotypically typical of Merkel cells.

Phenotypic analysis of cultured melanoma cells. Expression of cytokeratin-type intermediate filaments by the M5 human melanoma cell line

Expression of intermediate filament (IF) isotypes was studied in six human and two murine melanoma cell lines. With one exception, these lines expressed IFs only of the vimentin type; neurofilament peptides, desmin and GFAP were not detected. However, the M5 human melanoma line also expressed extensive cytokeratin tonofilament arrays, as visualized by immunofluorescence with a panel of eleven monoclonal antibodies and hetero-antisera to cytokeratins; only the keratin 19-specific antibody BA16 did not react. By 2 D gel electrophoresis, five major keratin peptides were detected (keratins 7, 8, 13, 17 and 18), and an additional 57 kD peptide was detected on immunoblots with several antikeratin antibodies. Also observed in M5 cells was focal collapse of tonofilament arrays in mitotic cells. All the melanoma lines tested were positive for S100; M5 and two other cell lines were also positive for the 220-240 kD neuroectoderm-associated cell-surface differentiation antigen defined by monoclonal antibody UJ 127:11. In all the melanoma cell lines, secretion of extracellular matrix proteins (fibronectin, laminin and collagen type IV) was sparse or absent, and all were negative for the epithelial cell markers HMG-1 and HMG-2. Co-expression of keratin and vimentin by a melanoma cell line is discussed in the light of recent controversy concerning expression of cytokeratins by other neoplasms of putative neuroectodermal origins.

Merkel cell (small cell) carcinoma of the skin: immunohistochemical and ultrastructural demonstration of distinctive perinuclear cytokeratin aggregates and a possible association with B cell neoplasms

Three cases of Merkel cell (small cell) carcinoma of the skin are presented with immunohistochemistry for epithelial and neuroendocrine antigens. All three cases showed distinctive punctate perinuclear cytoplasmic positivity for cytokeratin which corresponded to aggregates of intermediate filaments, seen ultrastructurally in two cases. Epithelial membrane antigen was also identified in two cases. Only one case showed cytoplasmic positivity for neuron specific enolase, and immunostaining for a battery of polypeptide hormones was negative. The demonstration of cytokeratin perinuclear inclusions provides a distinctive immunohistochemical feature to aid in their diagnosis. Two of the three patients had chronic lymphocytic leukaemia years before the diagnosis of Merkel cell carcinoma. The possible association of lymphoproliferative disorders, particularly B cell tumours, and Merkel cell carcinoma is discussed.

Bidirectional differentiation in a large cell pleomorphic primary endocrine carcinoma of the skin (a variant of malignant Merkel cell tumour)

A primary endocrine carcinoma of the skin is described in which the tumour cells showed the unusual features of large size and marked nuclear pleomorphism. Ultrastructural examination revealed combined features of squamous and endocrine differentiation in the same cells, a phenotype which has been previously anticipated but only recently described in endocrine carcinomas of the skin. In addition, immunocytochemical staining showed the co-expression of cytokeratin and neurofilament. The globular masses of cytokeratin corresponded to paranuclear whorls of intermediate filaments and there was also strong and diffuse staining for neuron specific enolase. Many tumour cells stained for calcitonin, VIP, ACTH, and S100 protein. Large tumour cells with markedly pleomorphic nuclei and co-expression of cytokeratin and neurofilament add to the expanding morphological spectrum of primary endocrine carcinomas of the skin.

Merkel cell tumor of the skin: an immunohistochemical study

Skin biopsy specimens from 12 elderly patients with Merkel cell tumors were investigated. Conventional light microscopy and immunohistochemical techniques were used. All of the tumors had similar morphologic features. Immunoreactivity for neuronspecific enolase, gastrin, calcitonin, and epithelial membrane-like antigen was demonstrated, and both neurofilaments and keratin filaments were observed. The immunohistochemical findings supported a Merkel cell origin for these Merkel cell tumors. The co-expression of neuroendocrine and epithelial markers in Merkel cell carcinomas is suggestive of neuroendocrine differentiation in a neoplasm of epithelial origin. Merkel cell carcinomas share many characteristics with neuroendocrine tumors of the bronchopulmonary and gastrointestinal tracts. All of these neoplasms may originate from cells of similar types that are present in several organs.

Variability of expression and arrangement of cytokeratin and neurofilaments in cutaneous neuroendocrine carcinomas (Merkel cell tumors): immunocytochemical and biochemical analysis of twelve cases

Twelve specimens of cutaneous neuroendocrine carcinomas (Merkel cell tumors) available as fresh tissue were analyzed for intermediate filament (IF) expression by immunocytochemical and biochemical methods. In immunofluorescence microscopy, most cases were positive for both simple-epithelium-type cytokeratins and the neurofilament L- and M-polypeptides. Several different IF staining patterns ranging from presence of plaque-like structures (fibrous bodies) only to nearly exclusive expression of delicate cytokeratin fibrils could be distinguished. In immunoelectron microscopy the labeling for both cytokeratin and neurofilament polypeptides seemed evenly distributed among the IFs of the fibrous bodies. In primary culture, tumor cells maintained the coexpression of both IF types. Desmoplakin-positive true desmosomes were found in 5 specimens. Biochemically, cytokeratins nos. 8, 18 and, variably, 19, as well as IT protein and, in many specimens, the neurofilament L-protein and a putative neurofilament M-protein were detected. Only traces of the neurofilament H-polypeptide were found. Our results show that a coexpression of cytokeratin IFs and neurofilaments in variable patterns is a characteristic feature of cutaneous neoendocrine carcinomas; occasionally, however, neurofilaments may be very scarce. The biological, histogenetic and diagnostic implications are discussed.

Differential expression of intermediate filament proteins distinguishes classic from variant small-cell lung cancer cell lines

The expression of intermediate filament proteins in classic and variant-type small-cell lung carcinoma (SCLC) cell lines was studied using immunocytochemical techniques, two-dimensional gel electrophoresis and immunoblotting assays. Classic SCLC cell lines contain cytokeratin proteins but no neurofilaments. In contrast, variant cell lines do not contain detectable amounts of cytokeratins but partly express neurofilaments and vimentin. These results explain apparent discrepancies on the intermediate filament content of SCLC described in the recent literature. The application of antibodies to fresh biopsy specimens of SCLC may in the future allow the identification of the variant type of cells in clinical SCLC specimens and may have a major impact on therapeutic strategy and prognosis in these patients.

Neuroendocrine skin carcinoma coexpressing cytokeratin and neurofilament proteins

Neuroendocrine (Merkel cell) carcinomas of the skin have been recognized as such for several years. Given the reported wide variability in the morphology and clinical evolution of these tumors, the notion that may they comprise several variants rather than a single type has been advocated. Electron microscopy has played a key role in the early recognition of these tumors while immunohistochemical studies for various neuroendocrine markers have facilitated their subsequent diagnosis and improved our understanding as to their complexity by the demonstration of immunoreactivity for NSE (neuron specific enolase) and a number of neuropeptides. There has also been considerable interest in the study of the cytoskeletal intermediate filament complement of neuroendocrine neoplasms in general and of those of the skin in particular. Early reports indicated that neuroendocrine skin carcinomas had neurofilaments while subsequent investigations determined that they had cytokeratin. However, more recent studies have indicated that at least some neuroendocrine skin carcinomas could in fact coexpress both aforementioned classes of intermediate filament proteins. This brief report is presented to confirm the latter investigations.

Identification of Merkel cells in human skin by specific cytokeratin antibodies: changes of cell density and distribution in fetal and adult plantar epidermis

Merkel cells are special neurosecretory cells which, in adult human skin, are usually very scarce. By immunofluorescence microscopy using antibodies to human cytokeratin polypeptide no. 18, we localized distinct non-keratinocyte cells in the glandular ridges of human fetal and adult plantar epidermis. Using electron and immunofluorescence microscopy, these cells were identified as Merkel cells containing typical neurosecretory granules as well as bundles of intermediate-sized filaments and desmosomes. Two-dimensional gel electrophoresis of the cytoskeletal fractions of microdissected epidermal preparations highly enriched in Merkel cells indicated the presence of cytokeratin polypeptides nos. 8, 18 and 19 which are typical of diverse simple epithelia of the human body. Double immunofluorescence microscopy showed that these human Merkel cells contain neither neurofilaments nor vimentin filaments. In human fetuses of 18-24 weeks of age, conspicuously high concentrations of Merkel cells, reaching a density of approximately 1,700 Merkel cells/mm2 skin, were found in the glandular ridges of plantar skin. The concentration decreased considerably at newborn and adult stages. Thin cell processes (up to 20 microns long) were observed in many fetal epidermal Merkel cells. In addition, we detected isolated Merkel cells deeper in the dermis (i.e. at distances of, at most, 100 microns from the epidermis) in fetal and newborn plantar skin. Our results show that Merkel cells are true epithelial cells which, however, differ profoundly from epidermal keratinocytes in their cytokeratin expression. The findings are discussed in relation to the much disputed question of the origin of Merkel cells. The present data speak against the immigration of Merkel cells from the neural crest, but rather suggest that they originate from epithelial cells of the skin, although most probably not from differentiated keratinocytes.