Study results suggest that the incidence of Merkel cell carcinoma (MCC) appears to be increasing dramatically in the United States. With an aging population and MCC disproportionately affected older adults, incidence rates are project to climb even faster in coming years.


 

Although the neuroendocrine skin cancer Merkel cell carcinoma (MCC) is less common than other skin cancer types, such as melanoma, research indicates that MCC is two to three times more likely to recur and be fatal than melanoma. Due in part to its lower incidence rates, physician awareness and education regarding MCC and its management are limited. And while reported incidence rates for MCC have continued to rise worldwide during the past decade, estimates of total annual United States incidence over the past 5 years are lacking. With a large population shift expected in the US within the next 10 years, and many Baby Boomers passing the 65-year-old threshold—after which MCC risk increases dramatically—Kelly Paulson, MD, PhD, Song Youn Park, MD, and colleagues sought to determine the current MCC incidence in the US and projected incidence through 2025.

 

Assessing the Data

For a study published in the Journal of the American Academy of Dermatology, the study team extracted 6,600 cases of MCC from the SEER-18 Database, which captures about 28% of the US population. “First, we determined changes in the total number of cases reported annually to the SEER database from 2000 to 2013,” says Dr. Park. “The number of cases reflects the incidence rate as well as the population at risk. For all solid tumors, we observed a 15% increase in the total number of cases, compared with 56% for melanoma and a remarkable 95% for MCC (Figure).”

Dramatic increases were also observed when Dr. Park and colleagues analyzed incidence as a function of age, with the effect found to be more pronounced in MCC than in melanoma or other solid tumors. “MCC incidence rates increased 10-fold between ages 40 to 44 and 60 to 64, and 10-fold again between ages 60 to 64 to 85 or older,” says Dr. Park. The fact that MCC rates continue to substantially rise among older patients, unlike with most cancers, was evident in the findings. In 2013, the median age at MCC diagnosis was 75 to 79 years for both men and women, compared with 65 to 69 for men with melanoma and 60 to 64 for women with melanoma. Additionally, 84% of patients with MCC were age 65 or older at diagnosis.

After cross referencing these results with US census data and 2014 national population projections, the researchers calculated the total number of new MCC cases in 2013 in the US to be 2,500, with projections of 2,800 new cases in 2020 and 3,200 in 2025. “This equates to a 30% increase of MCC cases over the next 10 years,” Dr. Park adds. He notes that these projections through 2025 may be underestimates. “We discovered that there has been about a 40% increase in incidence rate of MCC over the past 13 years (from 0.5 per 100,000 person-years in 2000 to 0.7 per 100,000 person-years in 2013,” he says. “To be conservative, we held the adjusted incidence rate stable for projections with the incidence rate observed between 2011 and 2013; thus, projections reflect only anticipated changes in population demographics.”

 

Applying the Findings

Dr. Park says she and her colleagues will continue to explore the changing epidemiology of MCC in other, bigger databases. She notes that, in terms of treatment, therapies that can overcome programmed cell death 1, or PD-1, axis inhibitor failure are urgently needed. In the meantime, the study team suggests that more MCC-specific provider education for proper management of this increasing disease may benefit patients, especially as the population ages. “Considering that MCC has a better prognosis in early stage disease, and immunotherapy can work better for metastatic MCC if it is used when tumor burden is lower, early detection and optimal management may improve patient outcomes,” says Dr. Park.