Looking at MCC Diagnoses Over Time Reveal Varying Effects Account for Incidence Rates

Changes in diagnostics and clinical awareness of Merkel cell carcinoma (MCC) suggest that resulting increased detection may have accounted for an initial increase in its incidence rate, according to the results of a study published in JAMA Dermatology.

Moreover, projected incidence rate increases for the coming years were found to likely be associated with the aging population examined and increased risk factor exposure in more recent birth cohorts.

“Despite the MCC incidence continuing to increase, the rate of increase appears to be slowing in recent periods, with most new cases associated with the aging population and risk factor exposure as opposed to clinical detection factors,” wrote the investigators.

From the period of 2012 to 2016, the data examined found an age-adjusted MCC incidence rate of 0.66 per 100,000 (95% CI, 0.62-0.70), which was a 3.5-fold (95% CI, 3.0-4.2) increase from the period of 1987 to 1991.

Additionally, the investigators observed the incidence rate of MCC increase with patient age across different time periods and birth cohorts. Specifically, the highest increase in incidence rates was observed in patients aged 85 years or older with age-adjusted rates from 2012 to 2016 observed at 14.6 per 100,000 men and 5.5 per 100,000 women.

While an increase over time has been observed for the birth cohort effect, the period of diagnosis has seen a plateau in incidence rates. The investigators project 3023 new cases of Merkel cell carcinoma in the year 2020 and 5130 new cases in the year 2030, which would signal an increase from the previous projection of 1933 cases in the year 2010.

“We show that, while MCC continues to increase in older populations, the incidence rate is projected to remain largely constant in younger populations,” the investigators wrote. “Furthermore, the rate of incidence increase appears to be slowing in recent calendar periods. Despite this slowing, the birth cohort effect does not appear to be plateauing.”

This longitudinal cohort study analyzed 3720 patients, 2200 of whom were men (59.1%) and a median age of 77 years (interquartile range, 68-84 years). The investigators sought to analyze age effects, period of diagnosis effects, and birth cohort effects over time.

The study was limited by the small sample size, with the 9 registries examined covering only 9.4% of the population. Because of this, the age-period cohort analysis was conducted by 5-year intervals, limiting the ability to recognize granular differences over shorter time periods. More, interpretation of the data is limited because the Surveillance, Epidemiology, and End Results Program database, from which the registries were accessed, does not contain information on patient comorbidities, medications, or patient information regarding polyomavirus status.

Looking ahead, the investigators suggest focusing attention on continued epidemiologic and clinical research to prevent this disease. Further context and investigation into trends based on racial/ethnic data, as well as epidemiologic evaluation, are warranted.

“This study aids in clinician understanding of Merkel cell carcinoma epidemiologic characteristics and helps to inform the need for continued aggressive risk factor modification and potential screening of patients older than 65 years,” the investigators concluded.

Reference:

Jacobs D, Huang H, Olino K, et al. Assessment of age, period, and birth cohort effects and trends in Merkel cell carcinoma incidence in the United States. JAMA Dermatology. Published November 4, 2020. doi:10.1001/jamadermatol.2020.4102