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

Multidisciplinary Approach to the Diagnosis of Occult Primary Neuroendocrine Neoplasm: A Clinical Challenge

Approximately 11% to 14% of subjects with neuroendocrine neoplasms (NENs) have metastatic lesions with unknown primary origin (UPO), with the majority of UPO-NENs found in the small bowel. Herein, we assessed the available literature on UPO-NENs, focusing on clinical presentation and diagnostic techniques to identify the primary site. The identification of the primary tumor is important as it affects the prognosis; however, the clinical presentation can be non-specific in non-functioning forms. In the presence of metastatic disease, the histological sample is fundamental to obtain immunohistochemical markers that might orientate the clinician in the search for the primary tumor through radiology, functional imaging and endoscopic techniques. In summary, multidisciplinary management plays a key role in UPO-NENs, even more than in other NENs. Molecular biology and gene-expression profiling represent areas of great interest which might be developed in the near future for both the diagnosis and the treatment of these neoplasms.

Metastatic Neuroendocrine Neoplasms of Unknown Primary: Clues from Pathology Workup

Simple Summary

While most neuroendocrine neoplasms are indolent and slow-growing tumors, subsets of cases will spread beyond the tissue of origin. Given the rather slow progress, some lesions are incidentally discovered as metastatic deposits rather than primary masses. In these cases, a biopsy is often taken to allow the pathologist to identify the tumor type and possibly the primary tumor site via microscopic examination. In this review, the authors present a simplified guide on how to approach metastatic neuroendocrine tumors from a pathologist’s perspective.

Abstract

Neuroendocrine neoplasms (NENs) are diverse tumors arising in various anatomical locations and may therefore cause a variety of symptoms leading to their discovery. However, there are instances in which a NEN first presents clinically as a metastatic deposit, while the associated primary tumor is not easily identified using conventional imaging techniques because of small primary tumor sizes. In this setting (which is referred to as a “NEN of unknown primary”; NEN-UP), a tissue biopsy is often procured to allow the surgical pathologist to diagnose the metastatic lesion. If indeed a metastatic NEN-UP is found, several clues can be obtained from morphological assessment and immunohistochemical staining patterns that individually or in concert may help identify the primary tumor site. Herein, histological and auxiliary analyses of value in this context are discussed in order to aid the pathologist when encountering these lesions in clinical practice.

Merkel cell carcinoma with partial B-cell blastic immunophenotype: a potential mimic of cutaneous richter transformation in a patient with chronic lymphocytic lymphoma

Merkel cell polyomavirus (MCPyV) is a DNA virus whose pathogenic mechanisms in Merkel cell carcinoma (MCC) are still being unraveled. Emerging reports of an association between MCPyV and chronic lymphocytic lymphoma (CLL) have begun to broaden our understanding of the oncogenic mechanisms of this virus and the known association between these 2 malignancies. Herein, we report a case of MCC demonstrating a B-cell immunophenotype arising in a patient with CLL being treated with rituximab. In this context, we discuss the differential diagnostic considerations, especially with cutaneous Richter transformation (diffuse large B-cell lymphoma). We also assessed for the presence of MCPyV in both the patient's MCC and the CLL. Finally, we provide a large meta-analysis of patients with CLL and MCC. Patients with both MCC and CLL have a dismal prognosis, with greater than 50% overall mortality within the first year and a half after MCC diagnosis.

Distinct gene expression profiles of viral- and nonviral-associated merkel cell carcinoma revealed by transcriptome analysis

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor with high mortality rates. Merkel cell polyomavirus (MCPyV), identified in the majority of MCC, may drive tumorigenesis via viral T antigens. However, mechanisms underlying pathogenesis in MCPyV-negative MCC remain poorly understood. To nominate genes contributing to pathogenesis of MCPyV-negative MCC, we performed DNA microarray analysis on 30 MCCs. MCPyV status of MCCs was determined by PCR for viral DNA and RNA. 1593 probe-sets were differentially expressed between MCPyV-negative and -positive MCC, with significant differential expression defined as at least 2-fold change in either direction and p-value of ≤ 0.05. MCPyV-negative tumors showed decreased RB1 expression, whereas MCPyV-positive tumors were enriched for immune response genes. Validation studies included immunohistochemistry demonstration of decreased RB protein expression in MCPyV-negative tumors and increased peritumoral CD8+ T lymphocytes surrounding MCPyV-positive tumors. In conclusion, our data suggest that loss of RB1 expression may play an important role in tumorigenesis of MCPyV-negative MCC. Functional and clinical validation studies are needed to determine whether this tumor suppressor pathway represents an avenue for targeted therapy.

Distribution and ultrastructure of Merkel cell of the fishing bat (Myotis ricketti)

The distribution and ultrastructure of Merkel cells were described in detail in piscivorous bats through immunohistochemistry and transmission electron microscopy techniques. The findings indicated that Merkel cells are commonly found in raised-domes, hair follicles and in the basal epidermis of the skin from their back, abdomen, intercrural membranes, wing membranes and footpads. However, the density of Merkel cells is significantly higher in the footpad than in other places. These results suggested that there may be a link between Merkel cells and tactile sense, and also might imply that raised-domes with air-flow sensitive hairs played an important role in adjusting flying gestures by monitoring the air flow around the body. The ultrastructure of Merkel cells is similar to other vertebrates except having more intermediate filaments and larger granules.

Merkel Cell Carcinomas

Merkel cell carcinoma (MCC) is a rare and extremely aggressive skin cancer that arises from primary neural cells. It presents most commonly in the elderly and immunocompromised patients. Pathologically, MCC should be distinguished from extrapulmonary small cell lung cancer or metastatic small cell lung cancer or a small cell variant of melanoma. The prognosis is based largely on the stage of disease at the time of presentation. Therapeutic options for MCC include wide resection with or without adjuvant radiotherapy or chemotherapy. Novel therapies based on the understanding of the molecular aspects of MCC are currently being explored.

The pathology of extrapulmonary small cell carcinoma

Extrapulmonary small cell carcinomas (EPSCCs) are uncommon malignant neoplasms with a reported incidence of 0.1% to 0.4% in the United States. Since their first description in 1930, they have been seen in nearly every organ system. Like their more common pulmonary counterparts, EPSCCs are thought to arise from a multipotential stem cell. However, there is recent molecular evidence that small cell elements may arise as a late-stage phenomenon in the genetic progression of more organ-typical carcinomas. The morphologic, immunohistochemical, and ultrastructural features are similar to those described in pulmonary small cell carcinomas (PSCCs). The differential diagnosis of EPSCC includes PSCC, other neuroendocrine tumors, small round blue cell tumors, metastatic melanoma, lymphoma, and poorly differentiated non-small cell carcinomas. Molecular alterations reported to occur in EPSCCs include abnormalities described in PSCC and changes found in carcinomas more typically encountered in the organ from which they arise. In this article we discuss the pathology of EPSCC with a review of theories of histogenesis, sites of occurrence, diagnostic features, differential diagnosis, molecular alterations, and clinical behavior.

Second neoplasms in patients with Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma (MCC) has been associated with a high incidence of other skin tumors and hematological malignancies. The purpose of this study was to analyze data from the Israel Cancer Registry regarding the incidence of second neoplasms in patients with MCC and their impact on survival.

METHODS

Sixty-seven patients in whom MCC was diagnosed between 1983 and 1999 were included. Data were collected on age, gender and ethnic origin, dates of diagnosis of MCC and any other neoplasm, and date and cause of death, if applicable. Comparison of MCC-specific survival, estimated by the Kaplan-Meier product limit method, between patients with no other neoplasm and those with second primary tumors was performed by log rank test. Age-specific standardized incidence ratio (SIR) was calculated using 5751 age- and ethnic-matched malignant melanoma patients as a control group.

RESULTS

Seventeen patients (25%) had a second neoplasm before, concomitant with, or after the diagnosis of MCC; 2 of them also had a third primary tumor. The SIR was 2.8 (95% CI; range, 1.38-4.22), significantly higher than the control group. Almost half the tumors were squamous cell carcinomas, either skin or head and neck, and most of the remainder were hematological malignancies or breast and ovarian adenocarcinomas. On univariate analysis, the presence of another neoplasm, regardless of its chronology, was associated with higher MCC-specific mortality (65% vs. 40% for patients with MCC only; P = 0.022). Analysis of only those patients in whom a second neoplasm developed during follow-up after treatment for MCC yielded an estimated actuarial risk of developing a second primary of 2.1% for each year of observation.

CONCLUSIONS

There is a high incidence of second neoplasms, including noncutaneous solid tumors, in patients with MCC. The presence of these neoplasms, whether they appear before, after, or simultaneously with MCC, is associated with a higher MCC-specific mortality.

Fine-needle aspiration diagnosis of unusual cutaneous neoplasms of the scalp in HIV-infected patients: a report of two cases and review of the literature

We report on two unusual, non-AIDS-defining scalp neoplasms, Merkel-cell carcinoma (MCC) and malignant melanoma, in 2 men with acquired immunodeficiency syndrome (AIDS). In the first patient, metastatic MCC was initially diagnosed by fine-needle aspiration (FNA) of a posterior cervical lymph node, based on the cytomorphology and the characteristic immunohistochemical and ultrastructural features. No skin lesion was initially apparent, but a 0.3-mm scalp primary was found during the ensuing neck dissection. In the second patient, recurrent and metastatic malignant melanoma from a Breslow 1.3-mm scalp primary was diagnosed by FNA. Both patients developed generalized disease in a relatively short time, despite their small primaries. These cases illustrate the occurrence of Merkel-cell carcinoma and melanoma in AIDS patients, and stress the need to consider these unusual cutaneous neoplasms when evaluating lymph node FNA samples from HIV-positive patients, especially since both may present as metastases from clinically occult primaries.

Merkel cell carcinoma of the skin

BACKGROUND

Neuroendocrine/Merkel cell carcinoma (MCC) of the skin is an uncommon tumour. Currently, there are only limited data available on the natural history, prognostic factors, and patient management of MCC.

OBJECTIVES

To review our experience and build the largest database from the literature.

METHODS

Twenty-eight cases from the London Regional Cancer Center were combined with 633 cases obtained from the literature searched in English, French, German, and Chinese for the years 1966 to 1998. The database included age, sex, initial disease status at presentation to the clinic, site of primary, any coexisting disease, any previous irradiation, sizes of primary/nodal/distant metastases, management details, and final disease status. A new modified staging system was used: stage Ia (primary disease only, size > 2 cm), stage Ib (primary disease only, size > 2 cm); stage II (regional nodal disease), and stage III (beyond regional nodes and/or distant disease).

RESULTS

Age > 65 years, male sex, size of primary > 2 cm, truncal site, nodal/distant disease at presentation, and duration of disease before presentation (< or =3 months) were poor prognostic factors. Surgery was the initial treatment of choice and it significantly improved overall survival (p =.004).

CONCLUSIONS

We identified poor prognostic factors that may necessitate more aggressive treatment. The suggested staging system, incorporating primary tumour size, accurately predicted outcomes.

Chemotherapy in neuroendocrine/Merkel cell carcinoma of the skin: case series and review of 204 cases

PURPOSE

To study the use of chemotherapy for Merkel cell carcinoma (MCC) of the skin.

PATIENTS AND METHODS

Twenty-five cases of MCC were treated at the London Regional Cancer Center between 1987 and 1997. Thirteen cases treated with chemotherapy were reviewed with 191 cases from the literature.

RESULTS

At presentation, 24 patients had localized skin lesions (stage I) and one had locoregional involvement (stage II). Among the nine cases with recurrent nodal disease, six had chemotherapy as a component of salvage treatment. They were all free of disease at a median of 19 months (range, 12 to 37 months). In contrast, two patients who had salvage radiotherapy alone died of disease. Overall survival (OS) and disease-free survival (DFS) were 59% and 43%, respectively, at two years. Median OS and DFS were 29 months (range, 1 to 133 months) and 9 months (range, 1 to 133 months), respectively. Nodal disease developed in 12 (50%) of 24 patients with stage I disease, and distant metastases developed in six (25%) of 24. Including those from the literature, there were 204 cases treated with chemotherapy. Cyclophosphamide/doxorubicin (or epirubicin)/vincristine combination +/- prednisone was the most commonly used chemotherapy regimen (47 cases), with an overall response rate of 75.7% (35.1% complete, 35. 1% partial, and 5.4% minor responses). Etoposide/cisplatin (or carboplatin) was the next most commonly used regimen (27 cases), with an overall response rate of 60% (36% complete and 24% partial responses). The difference in response rate was not statistically significant (P =.19). Among the 204 cases, there were seven (3.4%) toxic deaths.

CONCLUSION

Chemoradiation for locally recurrent or advanced disease may be an option for patients with a good performance status.

Small cell sweat gland carcinoma in childhood

Sweat gland carcinomas are rare skin tumors that typically occur in older patients. The spectrum of their clinical and pathologic features is broad, and many different types of sweat gland carcinomas have been described, ranging from fairly indolent to highly aggressive neoplasms. We present two cases of sweat gland carcinoma with a predominant small cell morphology. Both tumors occurred in children. One lesion developed in an 8-year-old girl as an asymptomatic papule on her left forearm, which ultimately was evaluated using biopsy because of rapid growth and change in color. The other lesion occurred on the hand of a 12-year-old boy. Both tumors were pandermal and extended into fat. They were composed of monotonous cuboidal cells with scant cytoplasm that formed tubules and grew in anastomosing cords and trabeculae. The tumor cells were immunoreactive for cytokeratins but not for cytokeratin 20. Ultrastructural analysis (available in one case only) showed that the tumor cells lacked neurosecretory granules. This variant of sweat gland carcinoma needs to be distinguished from other small cell neoplasms of the skin, especially Merkel cell carcinoma, its closest mimic.

Merkel cell carcinoma of palatal mucosa in a young adult: immunohistochemical and ultrastructural features

The first case report of a merkel cell carcinoma arising from the palatal mucosa in a young adult is presented. The histopathological similarities of this tumour in skin and oral mucosa are also discussed. The patient was a 14-year-old female with a non-symptomatic painful swelling in the left molar region of the maxilla. Under the diagnosis of a malignant tumour, a partial maxillary resection was performed, but there was a recurrence, and finally the patient died of cerebral metastasis. The tumor was composed mainly of uniform small cells. Immunohistologically, a large number of the cells were reactive to neuron specific enolase (NSE) and cytokeratin CK19, and some of the cells were positive to CK8, CK13, CK20, PGP9.5 and CEA focally and slightly. Pseudo-rosette formation and squamous differentiation were frequently detected. The ultrastructure of the tumour cells showed abundant Golgi bodies associated with neurosecretory granules. We conclude that it is the first case of a Merkel cell tumour arising from palatal mucosa and invading underlying bone with reactive hyperplasia. These findings closely resemble those of the same tumour occurring in the skin

Merkel cell carcinoma

BACKGROUND

Merkel cell carcinoma is an aggressive tumor with nonspecific clinical features. The prognosis in general is worse than malignant melanoma. Local recurrence rates are high with one-third of patients having recurrence within one year of excision. The tumor invades blood vessels and lymphatics. This frequent lymphatic dissemination leads later to satellite lesions and recurrence. Distant metastases occur in one-third of patients. One-,two- and three-year survival rates are poor, being estimated at 88%, 72%, and 55%, respectively.

OBJECTIVE

To increase awareness of the behavior of this uncommon tumor.

METHODS

A review of the current literature and recommendations regarding this tumor.

RESULTS

Wide local excision with 3-cm margin shows significant reduction in local recurrence compared with 2-cm margins. Two-thirds of patients with local recurrence ultimately die from their disease. Radiation therapy has a role to play in the local and regional clearance of the tumor.

CONCLUSION

Prompt diagnosis and surgical excision are necessary to improve survival. Mohs micrographic surgery offers potential advantages in evaluating both the lateral and the deep margins. Follow-up studies of patients treated with this modality will be beneficial.

Primary cutaneous neuroendocrine tumors. Diagnostic use of cytogenetic and MIC2 analysis

Merkel cell carcinoma (MCC) is a primary cutaneous neoplasm most commonly involving older adults. The cell of origin is thought to be the Merkel cell, a cutaneous neurosecretory cell. However, other neuroectodermal tumors may present in the skin and may be difficult to distinguish from MCC, including peripheral neuroectodermal tumors (PNET) and metastatic small cell carcinoma. We examined a primary cutaneous tumor of an 18-year-old which was strongly positive for cytokeratin (CK), neuron-specific enolase (NSE), and 12E7, an antibody to the protein determined by the MIC2 gene. Electron microscopy showed paranuclear aggregates of filaments and no cytoplasmic processes. These findings were considered to be consistent with MCC. Cytogenetic analysis demonstrated 46,XX,der(1)t(1;3;22)(1qter-->pa34::3q28-->q11::22q 12--> qter),der(3)t(1;3)(3pter-->q11::1p35-->pter), der(22)t(3;22)(22pter-->q11::?3q29-->qter). This was confirmed by chromosome painting using probes for chromosomes 1, 3, and 22. Peripheral neuroectodermal tumors (PNETs) show a characteristic translocation involving the same breakpoint on chromosome 22 that was present in this tumor. PNETs can also be CK and NSE positive. The MIC2 gene codes for a surface glycoprotein that has been shown to be very strongly and reliably expressed in PNETs, but not in other small round blue cell tumors and not in small cell carcinoma of the lung. However, MIC2 expression has not been studied in MCC. We investigated the use of MIC2 analysis in the distinction of MCC from PNET. Five additional MCCs were stained with the monoclonal 12E7 antibody, and one additional tumor showed the strong membranous positivity reported in PNETs. Our data suggest that MIC2 analysis may be useful in differentiating between MCC and PNET. However, cases will remain for which the distinction is elusive and cytogenetic analysis may be helpful.

Further insights into the natural history and management of primary cutaneous neuroendocrine (Merkel cell) carcinoma

PURPOSE

Primary cutaneous neuroendocrine (Merkel cell) carcinoma is a rare neoplasm with aggressive behavior but potential for response to radiotherapy and chemotherapy. Optimal treatment regimens are evolving based on reports of case series and a growing understanding of the natural history.

METHODS AND MATERIALS

A retrospective analysis of 34 cases treated at two Australian Institutions over 13 years is presented, focusing on clinical features and response to therapy.

RESULTS

The aggressive nature of this neoplasm is confirmed by the local recurrence rate of 22% following surgical excision, the development of regional node metastases in 76%, and of distant metastases in 70%. Overall median survival was 24 months with 65% of patients succumbing to metastatic disease. An association with B cell malignancies and immunosuppressive therapy is noted, with these patients having a poorer outcome, and one spontaneous remission was observed. Radiation therapy produced responses in 21 of 30 measurable sites (11 complete, 10 partial), and in 11 sites irradiated prophylactically there was only one infield relapse (9%). Responses to chemotherapy were observed in 8 of 20 applications (40%), particularly carboplatin and etoposide given in the setting of regional node disease.

CONCLUSION

In this poor prognosis tumor, further investigation of adjuvant radiotherapy and chemotherapy is warranted, as responsiveness of recurrent disease is confirmed. Immunological factors appear important in the natural history, and their manipulation may offer additional therapeutic options.

Merkel cell carcinoma

A case of Merkel cell carcinoma of the cheek is described, highlighting the clinical behaviour, diagnosis and management of this uncommon tumour.

Immunohistochemical examination of 25 cases of Merkel cell carcinoma: a comparison with small cell carcinoma of the lung and oesophagus, and a review of the literature

Merkel cell carcinomas (MCC) were compared to small cell carcinomas of the lung (SCCL) and oesophagus (SCCO). Most MCC were of the intermediate cell type while SCCL and SCCO were usually of the small cell type. Only MCC of trabecular type could be separated from SCCL and SCCO by means of histopathological examination alone. All MCC (25) stained with cytokeratin CAM 5.2, 20 of which in a "paranuclear globular" or combined "paranuclear globular"/diffuse pattern while 17 MCC stained with cytokeratin AE1/AE3. Cytokeratin CAM 5.2 reacted with 60 percent of the SCCL and 86 percent of the SCCO, and cytokeratin AE1/AE3 with 33 and 28 percent respectively. Neurofilament stained 17 MCC in a "paranuclear globular" pattern but none of the SCCL and SCCO. All MCC with a diffuse staining pattern for cytokeratin CAM 5.2 were negative for neurofilament. The results of this study and review of the literature indicate that in most instances Merkel cell carcinoma can be separated from other SCC, pulmonary as well as extrapulmonary, by means of histopathological and, above all, immunohistochemical examinations.

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 of the lip (Merkel cell tumour) examined by electron microscopy and immunohistochemistry

A definite diagnosis of neuroendocrine carcinoma of the skin is seldom made on initial histological examination; the tumour is usually reported as a poorly differentiated or anaplastic carcinoma. By applying electron microscopy and immunohistochemistry, a correct diagnosis can be made. The ultrastructural examination shows dense-core membrane-bound granules, intermediate perinuclear filaments and desmosome-like junctions. Immunohistochemistry reveals positive staining for neuron-specific enolase and keratin, the latter in a characteristic paranuclear distribution. Confronted with an unusual clinical picture or indefinite histological diagnosis, tissue specimens should be secured for the above mentioned ancillary procedures.

Involvement of chromosome 22 in a Merkel cell carcinoma in a patient with a previous meningioma

The relatively simple cytogenetic findings in an aggressive metastatic Merkel cell carcinoma are reported. Deletion 2p was found in 100% of the cells. Nevertheless, this was considered a secondary (metastatic?) change because the same aberration has been found in several other kinds of malignancy. The involvement of chromosome 22 [del(22q) and -22] in 85% of the cells seemed more intriguing, considering the fact that the Merkel cell carcinoma followed a previous meningioma.

Synaptophysinlike immunoreactivity in the Merkel cells of pig-snout skin

Synaptophysin is a membrane glycoprotein (Mr 38,000) found in small vesicles with clear content. It is present in neurons and in a variety of neuroendocrine cells and neoplasms, including the neuroendocrine carcinoma of the skin (Merkel cell tumor). We report the presence of synaptophysinlike immunoreactivity in normal Merkel cells of the pig-snout epidermis and vibrissae. The immunostaining was primarily localized in the Merkel cell side opposite to the nerve terminal. This fact suggests that in Merkel cells, as well as in other neuroendocrine cells, synaptophysin could occur in small clear vesicles (accumulated in Merkel cells in the side opposite to the neurite) and not in the secretory granules themselves (which are concentrated in the cellular side apposed to the neurite).

Applications of immunocytochemistry to diagnostic cytopathology

Immunohistochemical technique is now successfully applied to the cytologic materials. This review article describes details of staining procedures for immunocytochemistry at both light and electron microscopic levels. The clinical application of the technique includes aspiration biopsy cytology for breast lesions, thyroid lesions, lymph nodes, the nervous system, and others. The establishment of carcinoma cells in the body fluid by the demonstration of carcinoembyronic antigen (CEA) and the establishment of specific diagnoses in small-cell or large-cell anaplastic tumors by immunocytochemistry warrants special emphasis.

Characterization of Merkel cells and mechanosensory axons of the rat by styryl pyridinium dyes

The epidermal Merkel cells and their sensory innervation serve tactile sensation in vertebrates. In this study the fluorescent cationic mitochondrial dye, 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (4-Di-2-ASP), which has recently been used as a vital stain for motor and autonomic nerve terminals, was tested for its ability to stain Merkel cells and sensory fibers in the snout of the rat. Brightly-fluorescent structures resembling Merkel cells as well as nerve fibers and their terminations were evident in whole mounts of the vibrissal follicle. Unilateral denervation of the vibrissal follicles soon after birth resulted in a staining pattern remarkably similar to that obtained after labelling of the Merkel cells selectively with the fluorescent marker quinacrine, but all fiber staining was abolished. Likewise, in the separated epidermis of other skin regions, including the hairy and glabrous skin of the nose, the staining pattern revealed by 4-Di-2-ASP was indistinguishable from that obtained by quinacrine fluorescence. These results indicate that certain styryl pyridinium dyes may be used as vital stains for epidermal Merkel cells as well as cutaneous mechanosensory axons.

[Clinical aspects and therapy of Merkel cell tumor--report of 4 personal cases and review of the literature]

Four cases of Merkel cell tumor located in the face or on the trunk are presented. In a literature review 339 cases were found and analysed. The Merkel cell tumor is a neuroendocrine tumor of the skin derived from the Merkel cells. It is located most often in the face and neck area. Typically, it is an exophytic node, has a red-blue color and measures 25 mm in diameter on the average. Since it is metastasizing it is a malignant tumor. Regional node metastases were found in 27%, local recurrences occur in 51%, and distant metastases were seen in 32% of the cases. The best therapy is excision with wide margins as is the rule for a malignant skin tumor. While the tumor reacts to radiotherapy, chemotherapy seems to be of no help.