Compared with White patients with Merkel cell carcinoma (MCC), non-White Hispanic patients more commonly presented younger than 70 years of age and were more often female. In addition, the most affected site was the upper limb/shoulder, which differs from what has been reported in previous studies.
Those are key findings from a retrospective study of national cancer data that was presented during a poster session at the annual meeting of the Society for Investigative Dermatology.
"Merkel cell carcinoma is an infrequent and aggressive form of neuroendocrine skin cancer that mainly impacts individuals of White ethnicity, with a general occurrence rate of 0.7 instances per 100,000 person-years," one of the study authors, Luis J. Borda, MD, chief dermatology resident at Eastern Virginia Medical School, Norfolk, Virginia, told this news organization. The incidence of MCC is increasing among all racial groups, especially in the Hispanic population, he added.
To determine how age, sex, and primary site of MCC differ in White vs non-White Hispanic patients, the researchers evaluated the 22 population-based cancer registries of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program from 2000 through 2020. They reported categorical variables as counts and percentages and used chi-square test with Yates's correction to assess the association between categorical variables.
Of the 17,920 MCCs identified by the researchers, 40 (0.22%) were in non-White Hispanic patients. Compared with the White patients with MCC, significantly fewer non-White Hispanic patients were age 70 years or older (50% vs 72.1%, respectively; P < .001), and MCC was more common in female non-White Hispanic patients (23, or 57.5%), while White patients with MCC were predominantly male (11,309, or 63.2%; P < .05). "This suggests that MCC in non-White Hispanic patients may involve different risk factors related to age beyond just cumulative UV exposure and aging-related immunosenescence, which may additionally account for the higher prevalence of females in this cohort, as historically male outdoor occupation has resulted in increased lifetime cumulative UV exposure," Borda said.
The head and neck were the most common sites of disease involvement in White patients (41.9% vs 27.5% in non-White Hispanic patients; P = .09), while the upper limb and shoulder were the most common sites of disease involvement in non-White Hispanic patients (37.5% vs 23.8% in White patients; P = .06). This finding "differs from previous studies showing head/neck being the most common site in Hispanics," Borda said, adding that this could be a result of White patients not being included in the Hispanic cohort in this study. "Because non-White Hispanic patients have darker skin, they may have proportionally more cases on sun-protected skin, as is described by the present data, suggesting that they are less likely to have UV-driven MCC."
The study "highlights distinct demographic and clinical characteristics of MCC among non-White Hispanic patients compared to their White counterparts, emphasizing the importance of considering race/ethnicity in understanding the epidemiology of this rare but increasingly prevalent cancer," Borda said. He and his coauthors are planning to do further research on the increasing incidence of MCC in non-White Hispanic patients and on staging at diagnosis compared to White patients."
Borda acknowledged certain limitations of the analysis, including the small sample size in the non-White Hispanic group, the retrospective nature of SEER data, selection bias, and the potential for underreporting.
He and his coauthors reported having no financial disclosures.