Merkel cell carcinoma – A population-based epidemiological study in Finland with a clinical series of 181 cases
Introduction
Merkel cell carcinoma (MCC) is a rare malignant neuroendocrine tumour of the skin. The incidence rates of MCC reported from different countries vary, but are not comparable because of differences in observation periods and in age-adjustment methods. In all studies, the incidence has been less than one per 100,000.1, 2, 3, 4, 5, 6
MCC affects mainly the white population with median age at presentation of approximately 70 years, and according to previous studies it is more common in men than in women.1, 2, 7, 8 The aetiology of MCC may be multifactorial. Exposure to ultraviolet radiation is associated with MCC.9, 10, 11 MCC also occurs more often in immuno-compromised individuals, such as those diagnosed with chronic lymphocytic leukaemia, lymphoma, or a human immunodeficiency virus infection, as well as amongst organ transplant recipients.12, 13, 14, 15, 16 Recently, a novel polyomavirus, named Merkel cell polyomavirus (MCPyV), was identified in MCC tumour tissue suggesting that a viral infection might also be an aetiological factor.17
Tumour size has been shown to be a strong prognostic factor,8, 18, 19, 20, 21 but the most consistent predictor of survival in MCC to date is the presence or absence of lymph node metastases at time of presentation.22 Sentinel node biopsy (SNB) is recommended for all patients with localised disease for the purpose of staging. The impact of SNB on survival is still unclear.7, 23 MCC has a high incidence of local recurrences and a propensity for regional and distant metastases. It is usually treated surgically, either with or without postoperative radiation therapy.
The aim of this study was to calculate the incidence and survival of MCC patients in Finland, and to present clinical characteristics of this large national patient series.
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Material and methods
Individuals diagnosed in Finland with MCC or small cell carcinoma of the skin up until 2008 were identified from the Finnish Cancer Registry. The Registry was set up in 1953, and it maintains a nation-wide population-based database on all cancer cases in Finland (population 5.4 million in 2010). All physicians, hospitals and pathology and haematology laboratories are obligated to submit data to the Finnish Cancer Registry on all cancer cases that come to their attention. The Registry has a
Incidence
Since the early years of the recognition of MCC, the incidence estimates have become more reliable, and since 1989 they have been fairly stable. The age-adjusted (world standard) incidence of MCC (per 100,000) in 1989–2008 in Finland was 0.11 for men and 0.12 for women (Fig. 1). The corresponding rates adjusted to the European standard population are 0.19 and 0.20, and to the US 2000 population 0.24 and 0.25.
The incidence increases sharply with age and is similar in both sexes (Fig. 2). Because
Discussion
The age-adjusted (world standard) incidence rates of MCC based on a nationwide Finnish cancer registry are 0.11 and 0.12 per 100,000 person-years for men and women, respectively. The incidence increased during the early years (1979–1993), but thereafter the incidence has stabilised. The data before year 1989 are most likely incomplete due to diagnostic difficulties before immunohistochemical techniques, and, therefore, probably do not reflect the real incidence. Increased awareness of MCC
Conflict of interest statement
None declared.
Acknowledgment
This study was funded by Helsinki University Central Hospital Research Fund.
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Diagnosis and treatment of Merkel cell carcinoma: European consensus-based interdisciplinary guideline – Update 2022
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