Merkel cell carcinoma: a clinical, histopathologic, and immunohistochemical review

Nationwide multidisciplinary consensus on the clinical management of Merkel cell carcinoma: a Delphi panel

Merkel cell carcinoma (MCC) is a rare and highly aggressive cutaneous neuroendocrine carcinoma. The MCC incidence rate has rapidly grown over the last years, with Italy showing the highest increase among European countries. This malignancy has been the focus of active scientific research over the last years, focusing mainly on pathogenesis, new therapeutic trials and diagnosis. A national expert board developed 28 consensus statements that delineated the evolution of disease management and highlighted the paradigm shift towards the use of immunological strategies, which were then presented to a national MCC specialists panel for review. Sixty-five panelists answered both rounds of the questionnaire. The statements were divided into five areas: a high level of agreement was reached in the area of guidelines and multidisciplinary management, even if in real life the multidisciplinary team was not always represented by all the specialists. In the diagnostic pathway area, imaging played a crucial role in diagnosis and initial staging, planning for surgery or radiation therapy, assessment of treatment response and surveillance of recurrence and metastases. Concerning diagnosis, the usefulness of Merkel cell polyomavirus is recognized, but the agreement and consensus regarding the need for cytokeratin evaluation appears greater. Regarding the areas of clinical management and follow-up, patients with MCC require customized treatment. There was a wide dispersion of results and the suggestion to increase awareness about the adjuvant radiation therapy. The panelists unanimously agreed that the information concerning avelumab provided by the JAVELIN Merkel 200 study is adequate and reliable and that the expanded access program data could have concrete clinical implications. An immunocompromised patient with advanced MCC can be treated with immunotherapy after multidisciplinary risk/benefit assessment, as evidenced by real-world analysis and highlighted in the guidelines. A very high consensus regarding the addition of radiotherapy to treat the ongoing focal progression of immunotherapy was observed. This paper emphasizes the importance of collaboration and communication among the interprofessional team members and encourages managing patients with MCC within dedicated multidisciplinary teams. New insights in the treatment of this challenging cancer needs the contribution of many and different experts.

Merkel Cell Carcinoma: From Pathobiology to Clinical Management

Simple Summary

Merkel cell carcinoma (MCC) is an uncommon type of skin cancer that carries a poor prognosis. It is seen predominantly in old age in sun-exposed body parts. Racial and geographical differences are seen in its occurrence. Viral infection and radiation exposure are the two leading factors implicated in its causation. Small, firm to hard nodule (usually in sun-exposed areas), red with a history of a rapid increase in size is a common personation of the disease. Other body parts such as upper limbs, trunk, and even lower limbs may be also involved. The disease is diagnosed by taking a tissue sample (biopsy) for examination, and other radiological investigations are needed to reach a proper diagnosis with the staging of the disease. There are various treatment options including surgery, radiotherapy, and chemotherapy. Surgery is the primary treatment option though some patients may not be the candidates for operation where other treatment options come into play.

Abstract

Merkel cell carcinoma (MCC) is an infrequent, rapidly growing skin neoplasm that carries a greater probability of regional lymph node involvement, and a grim prognosis in advanced cases. While it is seen predominantly in old age in sun-exposed body parts, the prevalence varies among different races and geographical regions. Merkel cell polyomavirus and UV radiation-induced mutations contribute to its etiopathogenesis. The clinical presentation of MCC lacks pathognomonic features and is rarely considered highly at the time of presentation. Histopathological examination frequently reveals hyperchromatic nuclei with high mitotic activity, but immunohistochemistry is required to confirm the diagnosis. Sentinel lymph node biopsy (SLNB) and imaging are advised for effective staging of the disease. Multimodal management including surgery, radiation therapy, and/or immunotherapy are deployed. Traditional cytotoxic chemotherapies may result in an initial response, but do not result in a significant survival benefit. Checkpoint inhibitors have dramatically improved the prognosis of patients with metastatic MCC, and are recommended first-line in advanced cases. There is a need for well-tolerated agents with good safety profiles in patients who have failed immunotherapies.

Spinal Metastasis from Merkel Cell Carcinoma in an Elderly Male

Merkel cell carcinoma is a cutaneous neuroendocrine malignancy that has an aggressive nature. Classically, it affects the elderly Caucasian population with a predilection for the sun-exposed areas of the body. Pathogenesis has been linked to ultraviolet radiation, immunosuppression, and the Merkel cell polyomavirus. Definitive diagnosis entails histologic evaluation and immunohistochemical staining. With its generalized appearance and tendency for metastasis, a high index of suspicion must be utilized. In this case, we present the unique presentation of Merkel cell carcinoma as a rapidly enlarging lymph node with metastatic disease to the spinal column presenting as new-onset low back and radicular pain.

Merkel cell carcinoma: An update and review: Pathogenesis, diagnosis, and staging

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous neuroendocrine cancer. It most commonly presents as an indurated plaque or nodule on sun-damaged skin in elderly patients and is characterized by high rates of local recurrence and nodal metastasis. Survival at 5 years is 51% for local disease and as low as 14% for distant disease, which underscores the aggressive nature of this tumor and challenges in management. Advances in immunology and molecular genetics have broadened our understanding of the pathophysiology of MCC and expanded our therapeutic arsenal. With this comprehensive review, we provide an update of MCC epidemiology, pathogenesis, clinical presentation, diagnostic evaluation and prognostic markers. The second article in this continuing medical education series explores the evolving landscape in MCC management.

Update on Merkel Cell Carcinoma: Epidemiology, Etiopathogenesis, Clinical Features, Diagnosis, and Staging

Merkel cell carcinoma (MCC) is a rare, highly aggressive tumor, and local or regional disease recurrence is common, as is metastasis. MCC usually develops in sun-exposed skin in patients of advanced age. Its incidence has risen 4-fold in recent decades as the population has aged and immunohistochemical techniques have led to more diagnoses. The pathogenesis of MCC remains unclear but UV radiation, immunosuppression, and the presence of Merkel cell polyomavirus in the tumor genome seem to play key roles. This review seeks to update our understanding of the epidemiology, etiology, pathogenesis, and clinical features of MCC. We also review histologic and immunohistochemical features required for diagnosis. MCC staging is discussed, given its great importance in establishing a prognosis for these patients.

Clinicopathological spectrum of a series of Merkel cell carcinomas diagnosed at a tertiary cancer referral center in India, with current concepts

Merkel cell carcinoma (MCC) is a rare, clinically aggressive primary cutaneous neuroendocrine carcinoma. The present series describes clinicopathological features of 16 MCCs diagnosed at a tertiary cancer referral center. Sixteen MCCs occurred in 10 men and 6 women (M/F = 1.6:1), between the ages 37 and 74 years (mean, 58.3; median, 58.6), commonly in lower extremities (7) (43.7%) and head and neck sites (5) (31.2%), followed by upper extremities (3) (18.7%) and abdominal wall (1). Tumor size varied from 0.5 to 9.9 cm. Histopathologically, most tumors were composed of round to oval cells, mostly arranged diffusely with hyperchromatic nuclei, including "sudden" pleomorphism in some tumors. Variable features included coexisting Bowen disease (2/16), along with squamous, pseudoglandular, and rhabdomyoblastic dedifferentiation, all in a single tumor. Immunohistochemically, tumor cells were positive for at least a single epithelial marker in all 16 cases (100%) cases, including CK20, mostly paranuclear "dot-like" (12/13, 92.3%); CK (8/9, 88.8%), AE1/AE3 (3/3, 100%), and CK7 (1/6, 16.6%), along with neuroendocrine markers (16/16, 100%), including synaptophysin (11/13, 84.6%), chromogranin (12/15, 80%), and CD56 (4/4, 100%). Among other immunohistochemical markers, positive CKIT/CD117 was positive in 3 of 3 tumors. Surgical resection was performed in 11 (100%) of 11 cases, with adjuvant chemotherapy offered in a single case. Two cases with large-sized tumors, along with another case developed lymph node metastasis, including 1 who later developed pulmonary metastasis. Two patients were free of disease and 2 were alive with disease. Merkel cell carcinomas exhibit a diverse histopathological spectrum, including coexisting Bowen disease and, rarely, rhabdomyoblastic dedifferentiation, in some cases. Optimal immunohistochemical markers include CK20, synaptophysin, chromogranin, and CD56 for a timely diagnosis. Surgical resection is the treatment mainstay. Large-sized tumors and MCCs showing dedifferentiation portend a relatively more aggressive clinical course. Other recent developments in this tumor are discussed herewith.

Merkel cell carcinoma in the left groin: A case report and review of the literature

Merkel cell carcinoma (MCC) is a relatively rare but aggressive primary neuroendocrine carcinoma of the skin. MCC frequently occurs on sun-exposed areas in elderly Caucasian patients and has a propensity for local recurrence, regional lymph node invasion and distant metastases. However, MCC occurring on sites that are not sun-exposed in Asian patients is extremely uncommon. The current study describes the case of a 66-year-old Chinese male who presented with an asymptomatic, smooth lesion in the left inguinal region, which was initially diagnosed as a malignant lymphoma. Upon histological and immunohistochemical analysis, the tumor was consistent with the diagnosis of an MCC. In conclusion, due to its low incidence rate and lack of characteristic clinical manifestations, the final diagnosis of MCC relies on the analysis of histological findings and immunohistochemical markers following lesion biopsy or resection. The present study aimed to report a case of MCC and present a brief literature review in order to bring attention to the diagnosis of this condition.

Digital Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare and biologically aggressive neuroendocrine tumour of the skin. Recent analysis of a surveillance, epidemiology and end results program has shown a statistically significant increase of 8% per year in the age-adjusted rates for MCC of the skin over the past 15 years. MCC commonly presents as a painless, rapidly growing, single red or purple cutaneous nodule. Diagnosis is often delayed until histopathological examination due to the relative rarity of the disease. MCC-specific immunohistochemical markers are available for definitive diagnosis, including anticytokeratin-20-positive stain and thyroid transcription factor-1-negative stains. Because there are no phase III trials to guide management, treatment is often tailored to the individual patient by integrating surgery, radiation and chemotherapy.

A Merkel-cell carcinoma metastatic to the tonsil: a case report and review of the literature

Metastatic tumors to the palatine tonsils are extremely rare, with nearly 100 cases reported. Only 3 cases of Merkel cell carcinoma of the skin metastasizing to the palatine tonsil have been reported. We present the interesting case of a 61-year-old man with an enlargement of the left palatine tonsil that caused a moderate narrowing of the oropharynx. Three years previously he had been treated for Merkel cell carcinoma (MCC) on skin of his left shoulder. A tonsillectomy followed by palatoplasty was performed. Immunohistochemical staining demonstrated a pronounced reaction for cytokeratin 20, chromogranin, and CD56 histodiagnostic markers. Immunohistochemical studies are useful diagnostic tools in the establishment of the diagnosis of MCC. Treatment includes wide local surgical excision of the tumor, radiotherapy, and chemotherapy. Considering the aggressiveness of MCC, an early diagnosis is critical to enable the choice of adequate therapy at an early stage.

The Merkel cell carcinoma challenge: a review from the fine needle aspiration service

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin that occurs primarily in elderly or immunocompromised patients. For this report, the authors reviewed the diagnostic challenges associated with MCC encountered on their fine-needle aspiration (FNA) service and also conducted an in-depth review of the literature on MCC. A computer search for patients who were diagnosed with MCC by FNA at the authors' institution from 2006 to 2010 was conducted, and 5 patients were selected for cytologic and immunochemical analyses based on their varied and diagnostically challenging clinical presentations. The 5 selected patients had clinical findings commonly associated with MCC, including advanced age (4 of the 5 patients were ages 75-85 years) and a history of previous malignancies (3 of the 5 patients had a history of previous malignancy), and 1 patient was diagnosed with a concomitant low-grade lymphoma. The patients and their disease illustrated the protean clinical presentation of MCC and the clinical and cytologic challenges associated with this neoplasm. The current findings indicate the need for cytopathologists to be aware of the deceptive presentation of this neoplasm and its cytologic and immunochemical features to correctly diagnose this insidious neoplasm.

Merkel cell carcinoma--pathogenesis, clinical aspects and treatment

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin demonstrating a high rate of recurrence and metastasis. Indeed, 5-year rates for MCC specific survival are only about 60%. Although MCCs' incidence is rapidly increasing, it is still a very rare tumour. In this regard, the American Cancer Society had estimated for 2008 almost 1500 new cases in the USA. Recently, the newly identified Merkel cell polyomavirus has been found associated with most of the MCC cases. Nevertheless, the pathogenesis of MCC is not yet fully understood. Here, we will summarize recent findings of the pathogenesis of MCC, present an overview of clinical aspects and discuss treatment options for MCCs.

Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin. The incidence of this rare tumor is increasing rapidly; the American Cancer Society estimates for 2008 almost 1500 new cases in the USA. Thus, the incidence of MCC will exceed the incidence of cutaneous T-cell lymphoma. Moreover, the mortality rate of MCC at 33% is considerably higher than that of cutaneous melanoma. These clinical observations are especially disturbing as we are only recently beginning to understand the pathogenesis of MCC. For the same reason, the therapeutic approach is often unclear; reliable data are only available for the therapy of locoregional disease.

Skin cancer in solid organ transplant recipients: advances in therapy and management: part I. Epidemiology of skin cancer in solid organ transplant recipients

Skin cancer is the most frequent malignancy in organ transplant recipients, 95% of which are nonmelanoma skin cancer, especially squamous cell and basal cell carcinomas. This paper also discusses the incidence of other tumors (eg, melanoma, Merkel cell carcinoma, and Kaposi sarcoma) that are also increased in organ transplant patients compared to the general population. Part I of this two-part series describes the latest data concerning the epidemiologic and pathogenic aspects of nonmelanoma skin cancer development in solid organ transplant recipients. This review also highlights the concept of "field cancerization," represented by extensive areas of actinic damage and epidermal dysplasia, which accounts for increased risk of aggressive skin cancer development in susceptible patients.

Expression of minichromosome maintenance proteins in Merkel cell carcinoma

OBJECTIVE

Minichromosome maintenance (MCM) nuclear proteins have barely been employed in the diagnosis of skin malignancies. We aimed to assess whether MCM immunohistochemistry can be utilized to examine tumour proliferation in Merkel cell carcinoma (MCC).

METHODS

In this pilot study, we studied skin specimens of eight patients with MCC. As a control, eight patients with cutaneous malignant melanoma (MM) were included. Immunohistochemistry was performed for MCM4, MCM6, MCM7, Ki-67, p53, and p21.

RESULTS

Protein expression of MCM4 (66.0 +/- 26.5% vs. 33.9 +/- 22.4%; P = 0.017), MCM6 (70.9 +/- 11.9 vs. 31.7 +/- 22.7; P = 0.0031), and MCM7 (76.5 +/- 16.4% vs. 34.9 +/- 25.5%; P = 0.0013) was significantly increased in tumour cells of MCC when compared to tumour cells of MM. Ki-67 immunoreactivity was also significantly higher in MCC than in MM (28.7 +/- 7.9 vs. 11.0 +/- 9.2; P = 0.0012). Immunolabelling of p53 (68.6 +/- 26.2 vs. 58.4 +/- 28.8; P = 0.46) and p21 (40.1 +/- 38.8 vs. 25.8 +/- 16.1; P = 0.35) was relatively high but not significantly increased in MCC when compared to MM.

CONCLUSION

Our preliminary data indicate that MCM immunohistochemistry may be a useful tool for the determination of tumour cell proliferation in MCC.

Merkel cell carcinoma: molecular pathogenesis, clinical features and therapy

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin. The incidence of this rare tumor is increasing rapidly; the American Cancer Society estimates for 2008 almost 1500 new cases in the U.S. Thus, the incidence of MCC will exceed the incidence of cutaneous T-cell lymphoma. Moreover, the mortality rate of MCC with 33% is considerably higher than that of cutaneous melanoma. These clinical observations are especially disturbing as we are only recently beginning to understand the pathogenesis of MCC. For the same reason, the therapeutic approach is often unclear; reliable data are only available for the therapy of locoregional disease.

Vascular density has prognostic value in Merkel cell carcinoma

Merkel cell carcinomas are aggressive tumours for which histological prognostic factors need to be established. This study examines the prognostic role of vascular density, based on CD34 immunohistochemical staining in Merkel cell carcinoma. Thirty-six cases of Merkel cell carcinoma were immunohistochemically stained for the endothelial marker CD34. Vascular density was assessed in the tumor and stroma with a Chalkley eyepiece graticule. The scores of vascular density were correlated with other clinical and histological parameters to determine the prognostic significance of tumor vascularity. Increased vascular density was shown to be significantly associated with a worse prognosis (P = 0.005). A 1-unit increase in total vessel score was associated with a 3.9 times increase in the risk of death (95% hazard ratio confidence limits 1.50-10.32). Other factors associated with a worse outcome included tumor size (P = 0.05), the presence of lymphovascular invasion (P = 0.03), and tumor mast cell count (P < 0.002). Increased vascular density is associated with a worse prognosis in Merkel cell carcinomas. Assessment of vascular density may assist in predicting clinical behavior in these tumors and in evaluating the effects of adjuvant therapy.

Complete spontaneous regression in Merkel cell carcinoma

Merkel cell carcinoma is a rare, aggressive, cutaneous malignancy of the elderly with a generally poor prognosis. Like all skin cancers, its incidence is rising. A few reports of spontaneous regression have been published. The case of a 67-year-old female patient who presented with a cheek Merkel cell carcinoma is described. Following biopsy it underwent complete regression with no evidence of residual tumour in the excision specimen taken seven weeks later. The current knowledge of Merkel cell carcinoma and the other cases of spontaneous regression described in the literature are reviewed.

Merkel Cell Carcinoma in a Male Breast: A Case Report

Merkel cell carcinoma is a rare skin neoplasm and has not been reported yet in a male breast. We present a case of 74-year-old patient who was referred to the breast clinic with a lump in his right breast, which led first to the core biopsy followed by radical mastectomy and axillary clearance. The clinical characteristics, gross, microscopic and immunohistochemical findings and management of this lesion are discussed. Surgical excision remains the main option for treating this lesion including prophylactic lymphadenectomy and local radiotherapy.

Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous cancer that predominately affects elderly Caucasians with fair skin and has a propensity for local recurrence and regional lymph node metastases. A variety of terms have been used to describe this tumor, including trabecular cell carcinoma, neuroendocrine or primary small cell carcinoma of the skin, and anaplastic cancer of the skin. Although the skin lesion is most commonly found on sun-exposed areas of the head and neck or extremities, it can occur on the trunk, genitalia, and perianal region. The median age is 69 years, but it may occur earlier and more frequently in immunosuppressed patients. Patients with MCC frequently present with a nonspecific erythematous or violaceous firm nodule or small plaque that may be surrounded by small satellite tumors. MCC usually arises in the dermis and extends into the subcutis. It may be difficult to accurately diagnose MCC by light microscopy alone and ancillary techniques, including electron microscopy and immunohistochemistry, may be necessary to make a definitive diagnosis. Management of MCC is dependent on stage of the disease and is hampered by its rarity and lack of randomized trials. Nonetheless, for localized disease most guidelines include wide local excision of the primary tumor either alone or with radiation therapy. Sentinel lymph node biopsy can be helpful in staging and prognosis, but its benefit in survival remains to be seen. Systemic chemotherapy, akin to regimens for small cell carcinoma of the lung, may be considered as an adjuvant following surgery or to treat locoregional or distant disease. The prognosis of MCC is variable. Some patients with localized disease have an indolent course and are well controlled with local excision alone. On the other hand, many tumors are aggressive and have a tendency for locoregional recurrence and distant metastases. Such patients have a grim prognosis with a median survival of 9 months. Successful outcomes are most often seen in patients with early diagnosis and complete excision.

The Wnt-signaling pathway is not implicated in tumorigenesis of Merkel cell carcinoma

BACKGROUND

The Wnt-signaling pathway, involving beta-catenin, apc, and axin, plays a critical role in numerous developmental events. Alterations in the Wnt-signaling pathway have been detected in a wide variety of neoplasms. However, similar aberrations have not been described in Merkel cell carcinoma (MCC). The aim of this study was to determine the status of the Wnt-signaling pathway in MCC.

METHODS

Twelve cases of MCC were tested for the expression of beta-catenin and mutational status of CTNNB1 (gene for beta-catenin), APC, AXIN1, and AXIN2. Genomic DNA extracted from paraffin blocks was subjected to a polymerase chain reaction/single-strand conformation polymorphism analysis and sequencing.

RESULTS

Nuclear accumulation of beta-catenin was observed in only one case (8.3%), as determined by immunochemistry. No mutations were found in CTNNB1, APC, and AXIN2 in all cases, although silent mutations in AXIN1 were detected in three cases.

CONCLUSIONS

We conclude that the Wnt-signaling pathway does not play an important role in tumorigenesis in MCC.

The Toker Tumor

Primary neuroendocrine carcinoma of the skin is a relatively rare tumor that was first described by Cyril Toker in 1972. Since the seminal paper by Toker based on simple morphologic observations and detailed clinical correlation, our understanding of the clinical, morphological, and biological attributes of these lesions has grown exponentially with their increased awareness by pathologists and clinicians as well as with the many contributions of modern diagnostic techniques. The present review focuses principally on the various morphologic appearance that these tumors are able to adopt, the role of modern special techniques for diagnosis, and the conditions that need to be considered in their differential diagnosis.

Merkel cell tumour of the external ear. Report of a case

Merkel cells carcinoma (MCC) is an uncommon skin lesion, considered a malignancy of the neuroendocrine system, which is found mainly in elderly people. Its incidence is highly correlated with sun exposure or immunodeficiency syndromes. MCC is often an aggressive tumour with high tendency for local recurrence, lymph node involvement and distant metastasis. To our best knowledge 20 cases originated from the auricle have been described, 2 of them arising from external ear canal. The authors report a case of the ear canal characterized by two others synchronous tumours and the occurrence of a malignant high grade lymphoma, in which contribute of the pathologist was essential for a critical review. MCC diagnosis is not always easy for its pathological and clinical features and it should always be considered in presence of lymphoma. A multidisciplinary approach is basic.

A second field metachronous Merkel cell carcinoma of the lip and the palatine tonsil confirmed by microarray-based comparative genomic hybridisation

Merkel cell carcinoma was diagnosed in a 79-year-old Caucasian woman. The tumour was localised to the upper lip and was in stage T2. After successful cryosurgery and a 7-year tumour-free period, a new tumour developed in her palatine tonsil. Histologically and immunohistochemically, this resembled the tumour in the lip. The regional lymph nodes were devoid of metastasis. The paraffin-embedded material of the two tumours and the unaffected lymphatic tissue were analysed with DNA microarrays for comparative genomic hybridisation to assess the genetic relationship of the tumours. In both tumours, regions on 2p and 10p were commonly over-represented, while 41 regions on chromosomes 1-4, 6, 8-9, 11 and 14-22 were commonly under-represented. Chromosomes 1, 3, 4, 16-18 and X were most frequently involved in the DNA losses. In gene copy numbers in the two tumours, 31 chromosome locations were found to be differently affected. The partly similar and partly different molecular patterns indicated a genetic relationship between the tumours and excluded the possibility that the tonsillar tumour was a metastasis. The findings suggest that a genetically altered field was the reason for the development of the tonsillar cancer; thus, it can be regarded pathogenetically as a second field tumour.

Merkel cell carcinoma: changing incidence trends

BACKGROUND

The objective of this study was to define the incidence trends of Merkel cell carcinoma (MCC), a rare and aggressive cutaneous malignancy.

MATERIALS AND METHODS

All cases of MCC of the skin between 1986 and 2001 were identified using the surveillance, epidemiology, and end results (SEER) program. Overall age-adjusted, gender-specific, age-specific, stage-specific, and regional incidence rates were calculated. All rates are per 100,000 and age-adjusted to the 2000 US standard population. Estimated annual percent change (EAPC) was calculated using a linear least squares model.

RESULTS

A total of 1,124 cases of MCC were identified in the SEER registries. The rate of MCC increased from 0.15 cases per 100,000 in 1986 to 0.44 cases per 100,000 in 2001. The EAPC for the time period was 8.08%. This was statistically significant (95% CI: 6.29, 9.90, P-value < 0.05). Age-specific incidence (5-year age groups) were highest in the elderly, 4.28 per 100,000 in the 85+ age group.

CONCLUSIONS

MCC incidence rates have increased threefold over the 1986-2001 period. Rates are highest in the elderly population. Further etiologic studies and identification of high-risk populations are warranted.