title: Merkel cell carcinoma: incidence, mortality, and risk of other cancers.
abstract: BACKGROUND
  Merkel cell carcinoma (MCC) is a rare skin cancer that was recently found to be associated with a polyomavirus and with immunosuppression, provoking new interest in its epidemiology. We conducted a nationwide study in Denmark to describe MCC incidence and mortality and the association between MCC and other cancers.
  
  
  METHODS
  We used data from Danish national health and population registers on MCC diagnoses, deaths, and population counts during the study period (1978-2006) to calculate MCC incidence rates, cumulative risks of MCC at age 100 years, and MCC mortality rates by tumor stage. We used Poisson regression to estimate the excess mortality rate ratio attributable to MCC and examined associations between MCC and other cancers diagnosed before and after the MCC diagnosis using standardized incidence rate ratios (SIRs). All statistical tests were two-sided.
  
  
  RESULTS
  Between January 1, 1978, and December 31, 2006, 185 persons were diagnosed with MCC in Denmark. MCC incidence between 1995 and 2006 was 2.2 cases per million person-years. In the first year after MCC diagnosis, 22% of persons with localized disease died compared with 54% of patients with nonlocalized disease; by 5 years after diagnosis, the proportions of MCC patients who had died increased to 55% and 84%, respectively. MCC incidence was statistically significantly increased more than 1 year after a diagnosis of squamous cell carcinoma of the skin (SIR = 14.6, 95% confidence interval [CI] = 8.4 to 25.6), basal cell carcinoma (SIR = 4.3, 95% CI = 2.7 to 6.6), malignant melanoma (SIR = 3.3, 95% CI = 1.1 to 10.3), chronic lymphocytic leukemia (SIR = 12.0, 95% CI = 3.8 to 37.8), Hodgkin lymphoma (SIR = 17.6, 95% CI = 2.5 to 126), and non-Hodgkin lymphoma (SIR = 5.6, 95% CI = 1.4 to 22.4). Squamous cell carcinoma (SIR = 12.1, 95% CI = 5.1 to 29.1) and chronic lymphocytic leukemia (SIR = 14.7, 95% CI = 3.7 to 58.8) occurred in statistically significant excess more than 1 year after MCC diagnosis.
  
  
  CONCLUSIONS
  These results support the existence of shared risk factors for MCC and other cancers. Heightened awareness of the association between MCC and other cancers, particularly squamous cell carcinoma and chronic lymphocytic leukemia, may facilitate earlier clinical detection and treatment of MCC, thereby improving patient survival.
authors.affiliation: Department of Epidemiology Research, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark.
authors.forename: Jeanette
authors.initials: J
authors.lastname: Kaae
authors.forename: Anne V
authors.initials: AV
authors.lastname: Hansen
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Biggar
authors.forename: Heather A
authors.initials: HA
authors.lastname: Boyd
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Moore
authors.forename: Jan
authors.initials: J
authors.lastname: Wohlfahrt
authors.forename: Mads
authors.initials: M
authors.lastname: Melbye
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D015266:Carcinoma, Merkel Cell / Q000175:diagnosis* / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology; D015986:Confounding Factors, Epidemiologic; D003718:Denmark / Q000453:epidemiology; D005260:Female; D015658:HIV Infections / Q000150:complications; D006801:Humans; D015994:Incidence; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D016609:Neoplasms, Second Primary / Q000175:diagnosis* / Q000453:epidemiology* / Q000401:mortality; D011159:Population Surveillance; D011379:Prognosis; D012042:Registries; D012307:Risk Factors; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology