Merkel cell carcinoma: Current US incidence and projected increases based on changing demographics

Abstract

Background: Merkel cell carcinoma (MCC) incidence rates are rising and strongly age-associated, relevant for an aging population.

Objective: Determine MCC incidence in the United States and project incident cases through the year 2025.

Methods: Registry data were obtained from the SEER-18 Database, containing 6600 MCC cases. Age- and sex-adjusted projections were generated using US census data.

Results: During 2000-2013, the number of reported solid cancer cases increased 15%, melanoma cases increased 57%, and MCC cases increased 95%. In 2013, the MCC incidence rate was 0.7 cases/100,000 person-years in the United States, corresponding to 2488 cases/year. MCC incidence increased exponentially with age, from 0.1 to 1.0 to 9.8 (per 100,000 person-years) among age groups 40-44 years, 60-64 years, and ≥85 years, respectively. Due to aging of the Baby Boomer generation, US MCC incident cases are predicted to climb to 2835 cases/year in 2020 and 3284 cases/year in 2025.

Limitations: We assumed that the age-adjusted incidence rate would stabilize, and thus, the number of incident cases we projected might be an underestimate.

Conclusion: An aging population is driving brisk increases in the number of new MCC cases in the United States. This growing impact combined with the rapidly evolving therapeutic landscape warrants expanded awareness of MCC diagnosis and management.

Keywords: MCC; Merkel cell carcinoma; epidemiology; incidence.

Figure 1. Changes in incidence of Merkel cell carcinoma (MCC) as compared to all solid tumors and melanoma, 2000–2013

Data were extracted from the SEER-18 database, which captures 28% of the US population. A) US annual incidence rate of Merkel cell carcinoma The US annual incidence rate, age and sex adjusted to the 2000 US standard population (cases per 100,000 persons per year). Bars represent 95% confidence intervals. B) Cases reported to SEER with year 2000 as reference. The change in number of cases reported to SEER-18 (which reflects incidence rate and number of persons at risk in SEER catchment area) are shown, normalized to year 2000. The total number of solid tumors reported (blue squares) increased by 15% between 2000 and 2013, as compared 57 percent for melanoma (purple triangles), and 95% for MCC (green circles).

Figure 2. Merkel cell carcinoma disproportionately impacts individuals >=65 years of age

A) Incidence rate by age. Incidence rate by age is shown for Merkel cell carcinoma (green circles, per 100,000 persons) and melanoma (purple triangles, per 6,667 persons). Unlike for melanoma, the incidence rate of MCC increases in individuals >= 85 years of age. N=6,600 cases of Merkel cell carcinoma and 251,437 cases of melanoma (all cases reported to SEER between 2000–2013 with associated age and sex information). 95% confidence intervals are shown. B) Relative incidence in men and women by age. Both MCC and melanoma have a strong male predominance in the oldest individuals. There are insufficient cases of MCC below age 50 to determine whether women in the ‘Gen-X’ and ‘Millenial’ generations will be at higher MCC risk relative to men, as they are for melanoma. Year 2013 only is shown due to rapid changes in melanoma risk for young women. Note that Y axis is on logarithmic scale.

Figure 3. Observed and projected MCC incidence

A) Explanation for ongoing brisk rise in MCC incidence. Projected change in US population based on US census projections (bars) with MCC incidence rate per 100,000 from 2011–2013 (red line) (most recent years of available data) overlaid. The baby boom generation in 2025 is indicated by the bracket (ages 61–79 in 2025) and account for much of the anticipated rise in MCC incidence. B) Observed incidence and projected annual incidence for MCC from 2000–2025, based on SEER-18 data and US census projections. Estimated number of cases in 2015 in the US is 2,472 cases and in 2025 3,284 new cases per year.