Neuroendocrine (Merkel Cell) Carcinomas of the Skin: An Ultrastructural Study of Nine Cases

Clinical Experience on Eight Cases of Merkel Cell Carcinoma

Merkel cell carcinoma is a rare neuroendocrine neoplasm of the skin. The tumor most frequently affects elderly patients, with a preference for the head and neck. Eight patients affected by Merkel cell carcinoma have been observed at the General Surgery Unit II of the “Istituti Ospitalieri” hospital in Cremona, each in different stages of the disease; 75% of the cases involved the extremities, and in nearly all of the cases the tumor was nodular in appearance, with an average diameter of 2.2 cm. In 2 cases, the tumor was associated with rheumatoid arthritis, suggesting a dependency on the part of the neoplasm on the immune disorder and on steroid treatment. The available data confirm that in stage I of the disease, surgical treatment should be associated with radiotherapy in order to control the development of local relapses or metastases over time. In this stage, we observed a survival of 34 months (range, 24-48). In stages II and III, survival time falls, with very short duration of responses and poor quality of life as a result of the administration of cytotoxic molecules. Bearing in mind that any local relapse tends to appear within 12 months of the removal of the primitive tumor, that lymph node metastases appear in almost half of the patients, and that metastases over time are manifested in over a third of patients, it is essential to adopt a treatment capable of balancing the demand for longer remissions with a better quality of life. In this situation, we observed that treatment with somatostatin analogues achieves interesting responses without side effects, which suggests a close biological relationship between the tumor and somatostatin and that making a careful assessment of the prognostic factors of the disease can guarantee a correct therapeutic choice.

Merkel cell carcinoma: a retrospective study on 48 cases and review of literature

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine tumor of the skin. Fourty-eight patients with MCC were observed at the Rare Hormonal Tumors Group of Cremona Hospital, 15 of these with unknown primary site. Due to rarity of Merkel cell carcinoma, clinical experience is generally limited. Data from our series confirm the current recommendations. Wide surgical excision must be associated with radiotherapy also in early stages in order to avoid local relapse and the rapid progression of disease. In advanced stages chemotherapy is the standard despite the short duration of responses and poor quality of life. The data of our series, characterized by a high demand for second opinion, offer some insight about the real rarity of the tumor, the difficulty of managing of disease in our country secondary to a wrong cultural approach to the problem, the indiscriminate use of molecules unnecessary and often expensive, the lack of protocols, and the presence of guidelines often ignored. This results in very poor survival associated with a very low quality of life, requiring to find the right direction towards a correct management of disease.

Merkel Cell Carcinoma with Pagetoid Spread

A case of Merkel cell carcinoma showing epidermotropism is presented. The neoplastic cells displayed dotlike immunoreactivity for cytokeratins and strong immunoreactivity for neuron-specific enolase. Although no neuroendocrine granules were found, characteristic paranuclear fibrous bodies were present.

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.

Cutaneous undifferentiated small (Merkel) cell carcinoma, that developed synchronously with multiple actinic keratoses, squamous cell carcinomas and basal cell carcinoma

Merkel Cell Carcinoma (MCC) is an uncommon undifferentiated neuroendocrine tumor, arising in skin mainly on sun-exposed areas. We present an unusual case of primary cutaneous undifferentiated small cell carcinoma that co-existed with six other lesions; 2 actinic keratoses, 3 squamous-cell carcinomas and a basal-cell carcinoma. HE stained sections revealed MCC located in the mid-dermis, co-existing with severe actinic keratosis. Immunohistochemically, the tumor cells reacted to cytokeratin 20, epithelial membrane antigen, chromogranin and neuron specific enolase. This is an unusual case of cutaneous MCC co-existing with six other different lesions. The concurrent development of MCC, squamous-cell and basal-cell carcinoma in the same patient indicates the pluripotent epidermal stem cell origin of these tumors. Further research is needed to enlighten the factors inducing this divergent differentiation.

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.

Combined neuroendocrine carcinoma of the skin (Merkel cell tumor) and trichilemmal cyst

We report a case of neuroendocrine (Merkel cell) carcinoma (NC) of the skin, associated with a trichilemmal cyst, showing pagetoid spread into the trichilemmal epithelium. The association of the two lesions may strengthen the hypothesis that NC originates from pluripotent stem cells of adnexal epithelium.

Merkel cell carcinoma of the skin: imaging and clinical features in 93 cases

Clinical, pathological and imaging data for 93 patients with Merkel cell carcinoma were reviewed. Median survival duration from the date of diagnosis was estimated using the Kaplan-Meier product-limit method. Survival durations of patients with no metastastic disease, with regional lymph node metastasis only and with distant metastases were compared using the Cox-Mantel log-rank test. The median age for patients with Merkel cell carcinoma was 70 years (range 35-91 years). The tumour occurred in 71 men and 22 women. The most common primary site was the head and neck region (64 patients), followed by the extremities (21 patients) and the trunk (10 patients). Median survival duration for the whole group was 33 months (range 2-140 months). Imaging studies of the primary sites were available for 10 patients and of metastatic sites for seven patients. Sonograms of the primary skin lesions showed single or multicentric hypoechoic nodules arising from the dermis and growing into the subcutaneous tissues. CT scans showed single or multiple minimally enhancing soft tissue nodules, in two instances associated with lytic bone erosion. The metastatic lesions were moderately hypoechoic on sonography and target-shaped with or without ring-enhancement on CT. Imaging studies have a limited role in diagnosis of the clinically evident primary skin lesions, but may be helpful in the assessment of the depth of the invasion and are crucial in the evaluation of regional and distant metastatic disease. If regional adenopathy is found then CT of the chest, abdomen and pelvis may be in order.

Merkel cell carcinoma. Diagnosis and treatment

BACKGROUND

Merkel cell carcinoma is an uncommon malignancy of the skin that often portends a poor prognosis. Since its first description by Toker in 1972, a plethora of case reports and articles regarding the etiopathogenesis and treatment have been published spanning multiple medical and surgical disciplines. Much confusion still exists regarding the diagnosis and treatment of this ominous tumor.

OBJECT

Through extensive review of the medical, surgical, and pathological literature, to collate the observations of multiple investigators and summarize these findings.

METHODS

Articles from journals of multiple subspecialties were carefully reviewed with particular emphasis placed on epidemiology, prognosis, histology, immunohistochemistry, electron microscopy, tumor origin, treatment, and work-up of Merkel cell carcinoma.

RESULTS

Merkel cell carcinoma is an aggressive malignant neoplasm. Local recurrence develops in 26-44% of patients despite therapy. Up to three-fourths of patients eventually develop regional nodal metastases with distant metastases occurring in one-third of all patients. Reported overall 5-year survival rates range from 30% to 64%.

CONCLUSION

Treatment recommendations unfortunately are based more on anecdotal than scientific data because of the rarity of the tumor and its recognized high risk. Most authors recommend wide local excision of the primary lesion and regional lymph node resection if lymph nodes are palpable followed by x-irradiation of both the postsurgical bed and lymph node basin. The role of elective lymph node resection in the absence of clinically positive nodes remains controversial.

A combined occurrence of neuroendocrine carcinoma of the skin and a benign appendageal neoplasm

A 76-year-old Japanese male presented with a subcutaneous nodule in the dorsal cubital region of the right arm. The center of the nodule showed typical features of neuroendocrine carcinoma of the skin. The peripheral portion showed epithelial islands of squamoid cells with horn cysts suggestive of benign appendageal tumor with pilar differentiation. The coexistence of two skin neoplasms in the same lesion would suggest that both tumors developed from common pluripotential stem cell.

Giant neuroendocrine (Merkel cell) carcinoma of the skin

An 82-year-old woman had a dark red to purple tumor on the left buttock that had gradually enlarged during the last 5 years. Although routine histologic examination was not sufficient for diagnosis, neuroendocrine carcinoma was diagnosed by immunohistochemical and ultrastructural studies. Immunohistochemical-positive reactions to neurofilament, cytokeratin, neuron-specific enolase, and epithelial membrane antigen were noted. Electron microscopically, membrane-bound, dense core granules that yielded a positive uranaffin reaction and intermediate filaments in the perinuclear area were observed in the cytoplasm of most tumor cells. Desmosome-like structure between them was also found. Approximately 6 months after local excision, metastatic lesions developed in the regional lymph nodes and liver.

Primary neuroendocrine carcinoma of the skin. Clinicopathologic study of 18 cases

The clinical and pathologic features of primary neuroendocrine carcinoma of the skin in 18 elderly patients are reported. The carcinomas arose in the dermis and subcutaneous tissues, particularly on the head and the upper extremities. One tumor occurred in an irradiated area. Using Gould's clinicopathologic classification, we have found four trabecular types, eleven intermediate cell types, and two small cell types. One tumor could not be classified. Other noteworthy pathologic features were association with invasive squamous cell carcinoma, lentiginous melanocytic hyperplasia, and presence of intratumoral melanocytes. Immunoreactivity for cytokeratins (56 kD), neurofilaments, neuron-specific enolase, and epithelial membrane antigen was observed. The paranuclear globular staining pattern of cytokeratins and neurofilaments was conspicuous. The ultrastructural features revealed paranuclear intermediate filament aggregates (fibrous bodies), neurosecretory granules, and cell junctions. In two metastatic tumors, high levels of catecholamines were found. The trabecular types were characterized by localized disease and a good prognosis. The patients with the small cell types died of distant metastases. Postoperative radiotherapy seemed to reduce the rate of local recurrences.

The essential role of radiation therapy in securing locoregional control of Merkel cell carcinoma

Between 1966 and 1987, 54 patients with non-disseminated Merkel cell carcinoma (MCC) were treated with curative intent at the University of Texas M. D. Anderson Cancer Center. The primary tumor site was in the head and neck in 38 patients. The majority of the patients (57%) were referred with locoregionally recurrent disease. For the whole group, survival was 30% after 5 years. Patients who presented with nodal involvement had a median survival of 13 months compared with 40 months for node-negative patients (p less than .04). Only 4/37 patients treated initially by surgery alone were locoregionally controlled, with a median time to recurrence of 4.9 months. Salvage with radiation therapy was attempted in 18 patients (after additional surgery in 14), but was successful in only four. The predominant failure pattern in this subgroup was distant metastases, occurring as a component of initial recurrence in 12/18 patients. Prior to 1982, the philosophy of initial therapy was to give postoperative irradiation only to patients with large primaries or nodal involvement. Subsequently, postoperative radiotherapy has been recommended routinely, and all five patients treated with this approach remain disease-free. In total, 31 patients (including 10 patients with gross disease) were irradiated at M. D. Anderson; only one developed an in-field locoregional recurrence as an initial site of failure. However, three marginal recurrences occurred. The median dose to the primary tumor, first echelon nodes, and supraclavicular nodes was 60, 51, and 50 Gy, respectively. Our current recommendation for initial treatment is excision of the primary tumor followed by irradiation with generous fields to include the primary tumor site and draining regional lymphatics to doses of 46-50 Gy in 2 Gy fractions. For gross unresected disease, 56-60 Gy is recommended. The role of adjuvant systemic therapy remains to be defined.

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.

Merkel-cell carcinoma of the pinna

Merkel-Cell carcinoma is a rare malignant skin tumour. It was first described as 'Trabecular Carcinoma' by Toker in 1972. Since then many reports have appeared in the literature, mainly in the dermatology, pathology and to a lesser extent, in the plastic surgery journals. Surprisingly, the topic is rarely discussed in the otolaryngology literature, though nearly fifty per cent of these tumours arise in the head and neck.

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.

Merkel tumor of the lower lip: a case report and updated review of the literature work performed at the University of Illinois

An unusual case of Merkel cell carcinoma of the lower lip with metastasis to the submental nodes is presented. Clinical similarities and the histopathologic and prognostic differences between this tumor and basal or squamous cell carcinomas of the head and neck area are discussed and the current thoughts for treatment are presented. The capricious clinical course and the aggressive nature of the Merkel cell tumor is emphasized. A review of the existing literature is also included in an effort to familiarize the head and neck surgeon with this relatively new but potentially lethal pathological cutaneous entity.

Merkel cell tumor

A Merkel cell tumor appeared on the left cheek of an 83-year-old female was reported. The tumor was located mainly in the dermis and infiltrated to the subcutaneous adipose tissue with an involvement of the blood vessels and lymphatics at the periphery. Electron-microscopically, few of the dense-cored granules and the single globular aggregates of intermediate filaments at the nuclear indentations were observed. Electron-microscopic uranaffin reaction proved positive reaction on the dense-cored granules. Half of the cytoplasmic border was smooth, while the rest had short projections. Desmosomes or junctional complexes were not detected among the tumor cells. Immunohistochemically, the cytoplasm of tumor cell showed positive reaction to both neuron-specific enolase (NSE) and keratin. The single globular positive spots of the latter were localized in accordance with the aggregates of intermediate filaments. These findings suggested a neurogenic origin with double differentiation, epithelial and neuroendocrine, of the Merkel cell tumor.

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.

Criteria for the diagnosis of primary endocrine carcinoma of the skin (Merkel cell carcinoma). A histological, immunohistochemical and ultrastructural study of 13 cases

Thirteen cases of primary endocrine carcinoma of the skin (Merkel cell carcinoma) were reviewed with the aim of defining the morphological, immunohistochemical and ultrastructural criteria for diagnosis. The tumour cells were characterized by their scanty cytoplasm, generally small uniform nuclei with finely dispersed chromatin and multiple small nucleoli. Nuclear shapes varied from round to spindle, with larger and pleomorphic forms predominating in 2 tumours. A striking feature seen in 12 tumours was the occurrence of a "ball-in-mitt" pattern represented by 1 or 2 crescentic tumour cells closely wrapped around an oval cell. Staining for neuron-specific enolase was the most consistent marker of the tumour and the characteristic juxtanuclear globular staining for keratin and cytokeratin and the occasional coexpression of neurofilament set this tumour apart from other cutaneous neoplasms, in particular, metastatic carcinoid tumours and oat cell carcinoma from the lung. The fine structural features of note were striking paranuclear or juxtanuclear whorls of intermediate filaments, seen in 7 cases, the presence of variable numbers of membrane-bound dense core granules of 80-150 nm diameter in all cases and cytoplasmic spinous or microvillous projections containing microfilaments in 4 cases. Less consistent characteristics of primary endocrine carcinomas of the skin included cell moulding, argyrophilia and immunohistochemical staining for ACTH, VIP and calcitonin. The high frequency of vessel invasion in this series is in keeping with the high rate of local recurrence, lymph node metastases and visceral dissemination reported. The distinction from other similar appearing tumours in the skin is discussed.

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.

A neuroendocrine (Merkel) cell carcinoma with coexisting intraepidermal squamous cell carcinoma of the skin. Its growth accelerated by an extrinsic factor

A case of neuroendocrine (Merkel) cell carcinoma with coexisting intraepidermal squamous cell carcinoma of the skin was studied histologically, immunohistochemically and ultrastructurally as well as with tissue-culture and transplantation into nude mice. The primary tumor found in the lower leg of a 68-year-old Japanese man had remained thumb-sized for five years and, after contusion, had begun to enlarge rapidly up to 5 cm in size during one month. The patient died of metastatic neuroendocrine cell carcinoma nine months after excision of the primary tumor. Histologically the primary tumor was composed of neuroendocrine cell carcinoma extending down to subcutaneous adipose tissue and a small amount of intraepidermal squamous cell carcinoma, not associated with a wide range of necrosis, hemorrhage, granulation tissue or fibrosis. The tumor cells of the former were diffusely positive for neuron-specific enolase. They contained a few secretory granules, 100 nm in diameter. The tumor cells both cultured in media and transplanted into nude mice died two months later. The present case is the first report of Merkel cell carcinoma in which the growth accelerated by an extrinsic factor was proved. Histogenesis of neuroendocrine cell carcinoma with coexisting squamous cell carcinoma is also discussed.

Merkel cell carcinoma of the eyelid

The clinical and pathological features of two Merkel cell carcinomas of the eyelid skin are reported. Both tumours occurred in the upper lid in elderly women and enlarged rapidly to form smooth, round nodules which projected from the lid surface anterior to the grey line. In one case the primary excision biopsy was followed by a wider excision in 1982, and the patient has been free from recurrence or metastases in the intervening period. In the second more recent case, the tumour was inadequately excised in 1984 and the lid was treated by radiotherapy: this patient is at present free from recurrence. Histological examination of each tumour revealed an identical morphology - characterised by the presence of uniform polyhedral cells with multiple nucleoli lying in nests and lobules within the dermis: mitotic figures were prominent. Immunohistochemical studies showed the cells to react positively with antisera against neurone-specific enolase, epithelial membrane antigen and met-enkephalin. Electron microscopy revealed only rare neuroendocrine granules in one tumour, and numerous granules in the other. Intranuclear rodlets were not identified and there was paucity of cell membrane attachment modifications.

Merkel cell tumour of the skin

Two cases of a rare neuroendocrine skin tumour (Merkel cell carcinoma) are reported. The tumour affects mainly old women and men. It has a great tendency to metastasize to lymph nodes and distant sites. The primary treatment is surgical but radiotherapy has an important role to play. Merkel cell tumours are capable of producing NSE and have also been documented to secrete calcitonin and ACTH. Difficulties in histological diagnosis are frequent. The definitive diagnosis can only be made by electron microscopic examination.

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.

Coexpression of neurofilament and keratin proteins in cutaneous neuroendocrine carcinoma cells

Four cases of neuroendocrine carcinomas (NECA) of the skin were studied by indirect immunofluorescence, using a monoclonal antikeratin antibody and a polyclonal antineurofilament antibody. Fifty to ninety percent and 80 to greater than 95% of the NECA cells stained with the antineurofilament antibody and the antikeratin antibody, respectively. Using double-labeling indirect immunofluorescence we could also demonstrate that, in 3 cases studied, some of the NECA cells, but not all, stained with both antikeratin and antineurofilament antibodies. These results, together with the recent knowledge of the intermediate filament protein type of normal Merkel cells (MC), tend to support the hypothesis that NECA cells do not originate from epithelial MC but from dermal neuroendocrine cells. A dual concept of intraepithelial MC and extraepithelial intradermal neuroendocrine cells, "from possible distinct origin," is proposed. Such a system has already been suggested for the neuroendocrine cells of the appendix and bronchial mucosae.

Neuroendocrine (Merkel cell) carcinoma of the vulva: a case report and review of the literature

The clinical and pathologic features of a vulvar neuroendocrine (Merkel cell) neoplasm are presented. Cytologic studies of material obtained from needle aspiration suggested that the tumor was a small cell neoplasm possibly of neuroendocrine derivation. The light-microscopic findings of sheets of small, uniform cells were consistent with a diagnosis of neuroendocrine tumor. The electron-microscopic characteristics, including the presence of neurosecretory granules, confirmed the diagnosis of a neuroendocrine (Merkel cell) carcinoma. Regional lymph node metastases were present at the time of initial surgery, and both local and distant metastases developed 8 months later. A comprehensive pretreatment metastatic evaluation is recommended. The role of chemotherapy for primary therapy is considered.

A study of intermediate filaments (cytokeratin, vimentin, neurofilament) in two cases of Merkel cell tumor

In two cases of Merkel cell tumor, the study of intermediate filaments, using monoclonal antibodies (vimentin, cytokeratin, neurofilaments), confirmed the double differentiation (neuroendocrine and epithelial) of this tumor as previously observed in histological, electron microscopical and histochemical analyses. Labelling of the tumor cells was positive with monoclonal antibodies against neurofilament proteins and cytokeratin.

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.

Cutaneous metastasis of a radiation-associated thyroid medullary carcinoma

The rare event of a single cutaneous metastasis occurred in a 37-year-old white man two years after a subtotal thyroidectomy for sporadic medullary carcinoma is reported. The endocrine nature of the tumor is revealed by the ultrastructural study, and the type of secretion by the biochemical assay of calcitonin (CT) in the serum and in the tumor tissue extract and by the PAP (peroxidase-anti-peroxidase) technique with anti-CT antibodies on paraffin sections. The cytological and histological findings are described. Some peculiar ultrastructural aspects are presented in details. The fact that the patient received a course of Rx therapy (3,000 rads) on the neck for cervical syringomyelia at the age of 20 years is stressed.

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.

Extrapulmonary oat cell carcinoma

Primary extrapulmonary tumors with histologic features indistinguishable from bronchogenic oat cell carcinoma are appearing with increasing frequency in the literature. These tumors have been described in the esophagus, stomach, pancreas, larynx, hypopharynx, salivary glands, nasal cavity and paranasal sinuses, thymus, small and large bowel, uterine cervix, endometrium, breast, prostate, urinary bladder, and skin. It is now widely believed that oat cell carcinoma is a poorly differentiated counterpart of carcinoid tumor and that both originate from an endocrine cell system. In this article, the authors review all cases of extrapulmonary oat cell carcinomas, which they were able to find in the English literature, and report personally studied examples of these tumors, occurring in the esophagus, stomach and urinary bladder. A closely related, if not identical, tumor arising in the skin is also described. It is emphasized that a wider recognition of these tumors is likely to lead to their more frequent diagnosis and possible treatment.

Primary neuroendocrine carcinoma of the skin (Merkel's cell carcinoma)

Primary neuroendocrine carcinoma of the skin (Merkel's cell carcinoma) is a rare tumor. Until recently 86 patients with this tumor have been described. Two cases of this tumor are presented. This neoplasm has a high propensity for lymphatic as well as hematogenous metastases. It presents as a dermal or subcutaneous nodule. Awareness of this condition may lead to earlier diagnosis and improved survival.

Neuroendocrine carcinoma of skin with simultaneous cytokeratin expression

An unusual tumor of the skin was removed from the thigh of a 52-year-old white male. By light microscopy, the tumor was composed of intermediate and small cells in sheets and clusters. Ultrastructural study of the tumor cells showed numerous dense core granules and dendritic cell processes as well as intermediate filaments and cell junctions frequently within the same cells. Most of the tumor cells were stained intensely by antibodies to neurone-specific enolase (NSE), a marker of cells of the central and peripheral nervous system. The neuropeptides met-enkephalin and vasoactive intestinal peptide (VIP) were also found in tumor cells. Immunohistochemistry furthermore demonstrated cytokeratin. Both the ultrastructural appearance and keratin content of this tumor set it apart from conventional Merkel cell (or trabecular) carcinoma of the skin in a manner analogous to bipartite (i.e., epidermoid and small cell) carcinoma of lung. The production of neuropeptides simultaneously with the production of keratin establishes this as a bipartite skin tumor (i.e., ectodermal and neuroectodermal phenotype). We suggest that at least some primary neuroendocrine tumors of the skin arise from multipotential ectodermal cells not of neural crest origin, as has been proposed for small cell carcinoma of lung.

Multiple neuroendocrine carcinomas (so-called Merkel cell tumours) of the skin. Report on two cases with unique clinical course

Two neuroendocrine carcinomas of the skin (so-called Merkel cell tumours) are presented. In both cases multiple tumour nodules developed within the course of the disease. The light and electron microscopic observations correspond with the findings reported in other neuroendocrine carcinomas. As a variable morphological and clinical pattern for these tumours seems to exist we consider our two cases with their unique clinical picture to be an obviously infrequent variant of this tumour disease, we propose for it the term "multiple neuroendocrine carcinoma syndrome".

Tumors of the diffuse endocrine system, histochemical and electron-optic aids, and pitfalls in diagnosis

Tumors of the Diffuse Endocrine System are a heterogeneous group of malignant neoplasms which have rather characteristic light microscopic and cytologic features. These are, however, not diagnostic and their identification with separation from non-neuroendocrine carcinomas require important adjunctive evaluations including histochemical analysis, immunocytochemical characterization and electron-optic identification of endocrine secretory products and paracrine effects in the cytoplasm of the neoplastic cells. The importance of proper classification cannot be over-emphasized because of the often considerable biologic and prognostic differences between neuroendocrine carcinomas and other types of carcinoma, notably metastatic carcinomas from the breast and the prostate. Furthermore, the separation of these lesions into two groups; a small cell type and those with large cells (carcinoid type) appears to have clinical significance in both diagnosis and response to therapy.

Immunostaining of neuron-specific enolase as a diagnostic tool for Merkel cell tumors

Conventional histologic examination of Merkel cell tumors may result in misdiagnosis because of the close similarities these tumors bear to either malignant lymphomas or certain undifferentiated carcinomas. The authors have previously reported that neuron-specific enolase (NSE), a specific marker for neuroendocrine cells, is present in normal Merkel cells and can be used as a marker to identify this cell type. In this study, 11 Merkel cell tumors, identified employing electron microscopy, were studied using immunostaining of NSE by the peroxidase-antiperoxidase method. Varying intensities of NSE immunoreactivity were found in the cytoplasm of all the neoplastic cells in the different cases. The uniformly stained cytoplasm formed a small rim surrounding the large, unstained nucleus. Immunostaining of NSE thus provides a simple and reliable method for the differential diagnosis of Merkel cell tumors from other primary skin tumors which, with the exception of some malignant melanomas, have been shown not to contain NSE immunoreactivity.

Merkel cell carcinoma: a malignant neuroendocrine tumour of the eyelid

Merkel cell carcinoma is a recently described tumour which may occur on the face of the elderly. We report such a lesion which presented as a cyst on the eyelid of an 88-year-old woman. This tumour differs from other tumours of the eyelids in its propensity for local and distant spread.

Merkel cells and Merkel cell tumors. Ultrastructure, immunocytochemistry and review of the literature

Certain monomorphic cellular tumors that occur in the dermis have been called trabecular carcinomas or Merkel cell tumors. Forty-six cases have been reported to date and the literature on these is reviewed here, with six additional cases reported. Cytologic features include sparse cytoplasm, dispersed chromatin with inconspicuous nucleoli in round nuclei and many mitoses. Trabeculae and pseudorosettes may be identified. Electron microscopy is required for definitive diagnosis. Like normal Merkel cells, tumor cells contain electron-dense granules (80-200 nm), 10 mm filaments and desmosomes. Filament-rich cytoplasmic spikes were found in four tumors. These resemble corresponding protrusions of normal Merkel cells and have not been described in other APUDomas.

Merkel cell carcinoma: a report of three cases with neurone-specific enolase activity

Three cases are described of a primary cutaneous neoplasm occurring in elderly patients, histological and immunohistochemical features of which support an origin from Merkel cells. Microscopically sheets of uniform small cells filled the dermis, often with a prominent trabecular pattern. Ultrastructurally the cells showed neurosecretory granules, tangles of microfilaments, scattered mitochondria and occasional intranuclear rodlets. Immunohistochemical staining for neurone-specific enolase was positive and for prekeratin was negative in each case. The definitive diagnosis of Merkel cell tumour can be made with a combination of electron microscopy and immunohistochemistry.

Merkel cell carcinoma of the skin: the structure and origin of normal Merkel cells

A series of 15 Merkel cell tumours of skin is reported. They occur dominantly on the head and neck and on the extremities of elderly women, frequently presenting as a reddish nodule. Three cases were associated with squamous carcinoma at the same site, an association deserving further study. There are two main patterns: the commoner one takes the form of a trabecular carcinoma in the dermis mimicking metastatic carcinoma, including oat-cell carcinoma and neuroblastoma: a dissociated-cell form mimicks malignant lymphoma. The triad of vesicular nuclei with very small nucleoli, abundant mitotic activity and apoptosis is so characteristic as to be virtually pathognomonic in conjunction with structural features. Argyrophilia is common, but Bouin fixation is necessary to demonstrate it regularly. Small round secretory granules (89 +/- 18 nm) with narrow haloes, and an abundance of intermediate size filaments are among the ultrastructural hallmarks. There is a close similarity between better differentiated tumour cells and normal Merkel cells. The neural crest origin of MC is in doubt both on the basis of studies of the development and regeneration of MC and from the study of Merkel cell tumours.