1. Over the past two decades, the incidence of Merkel Cell Carcinoma (MCC) in the Queensland region has increased by an average of 2.6% annually.
2. Compared to other reports worldwide, MCC occurred at a relatively higher rate in Queensland, a region with a predominantly fair-skinned demographic that is subjected to high levels of UV-radiation year-round. This epidemiological trend reinforces the possibility that UV-exposure can serve as a significant causative factor in Merkel cell carcinogenesis.
Evidence Rating Level: 2 (Good)
Study Rundown: The pathogenesis of MCC is multifactorial in nature. However, a primary etiology of MCC may be ultraviolet (UV) radiation, as cursory reports have observed a higher incidence of MCC in latitudes closer to the equator. In this study, authors retrospectively analyzed data for MCC in Queensland—a predominantly fair-skinned population exposed to high amounts of UV year-round—with the objective of comparing incidence and survival rates for the tumor in a region of high UV-exposure with data from elsewhere in the world. The results demonstrated a MCC incidence rate of at least double that of any other study globally; similar rates of fatality and metastases were observed. Furthermore, the analysis showed that MCC incidence increased by an average of 2.6% per year since 1993. A strength of this study was the large data sample specifically obtained from a region with high levels of UV-exposure. A weakness was the lack of access to tissue samples, which may have affected the reliability of the MCC diagnoses and the possibility that advanced diagnostics may have contributed to the results observed.
Relevant reading: Merkel Cell Carcinoma: Epidemiology, Target, and Therapy
In-Depth [retrospective cohort]: The Queensland Cancer Registry was screened for all patients with a diagnosis of MCC from 1993 through 2010. Incidence trends were analyzed using Joinpoint regression models, which quantified the annual percentage change and specified any significant changes to the trend. A total of 879 eligible cases were identified, and when standardized for average annual age (in order to compare to other studies), the incidence in Queensland over the last 5 years was 1.6 per 100,000 (95% CI, 1.5-1.8). Incidence for MCC increased by an average of 2.6% annually (95% CI, 1.1%-4.2%), which equated to an overall rise of 54% between 1993 and 2010. Higher rates were reported in men (2.5 per 100,000) than in women (0.9 per 100,000), and the age of diagnosis was lower in men (75.5 vs. 78.0 years). Cause-specific survival was 88% (95% CI, 84%-91%) after 1 year and 66% (95% CI, 60%-71%) after 5 years.
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