Correlation of Ultraviolet Radiation Levels With the Incidence of Cutaneous Squamous Cell and Merkel Cell Carcinomas in Non-sunbelt Locales in the United States: 2010-2017

BACKGROUND

Non-melanoma skin cancer (NMSC) is the most common human malignancy worldwide, with increasing incidence in the United States (US). Recent environmental data have shown that ultraviolet radiation (UVR) levels have increased in the US, particularly in the higher latitudes, but the potential impact of this on NMSC incidence is not well known, despite estimates that 90% of NMSC is due to sun exposure. Our exploratory study synthesizes environmental data with demographic and clinical data to determine whether UV indices (UVIs) and non-sunbelt (non-SB) locale (latitudes >40 degrees, which comprises most of the US) might contribute to incidence rates of two types of NMSC: cutaneous squamous cell and Merkel cell carcinomas.

METHODS

UVIs from 2010 to 2017 were obtained from the National Oceanic and Atmospheric Administration database and meshed with corresponding locales in the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database (version 8.4.0.1). Four SB and five NSB locales contained sufficient data for analysis. Linear mixed modeling was performed with the outcome variable of the age-adjusted incidence of NMSC cancer (comprised of cutaneous squamous cell carcinoma of the head and neck (CSCCHN) and Merkel cell carcinoma (MCC)), the two most common types of NMSC contained within SEER). Non-SB locale and percent of days with UVI >3 were independent variables.

RESULTS

Percent of days with UVI >3 increased during this period, as did the overall NMSC (combined CSCCHN and MCC) skin cancer incidence, though MCC incidence alone did not increase during our study period. Environmental factors that significantly contributed to the age-adjusted overall NMSC (combined CSCCHN and MCC) cancer incidence (per 100,000 individuals) included NSB locale (b=1.227, p=0.0019) and percent of days with UVIs >3 (b=0.028, p<0.0001), as well as clinical factors of percent white race and percent male, by linear mixed modeling.

CONCLUSIONS

Our results are limited by the completeness of the NOAA and SEER databases, and do not include basal cell carcinoma. Nevertheless, our data demonstrate that environmental factors, such as latitude in NSB locale and UVI indices, can affect the age-adjusted overall NMSC (defined as CSCCHN and MCC in this study) incidence even in this relatively short period of time. Prospective studies over longer time periods are needed to identify the extent to which these findings are clinically significant so that increased educational efforts to promote sun-safe behaviors can be maximally effective.

Diagnosis of metaplastic synovial cysts in clinical dermatology

Metaplastic synovial cysts are a rare clinical finding, with less than 70 cases diagnosed to date. These cysts are painful and can greatly impact patients' quality of life. The goal of this case report is to describe the manifestations of these cysts to aid in clinical diagnosis and management. We herein report a case of a 58-year-old male who presented with a bump on the lateral left knee. He experienced pain upon walking. Notably, he had a past medical history of left knee replacement 15 years prior to presentation. Upon physical exam, the bump resembled a firm subcutaneous nodule. It was subsequently biopsied via eight-mm punch excision, revealing a metal portion of the patient's knee replacement; biopsy resulted in the removal of the entire bump. Biopsy results showed a cystic space in the deep dermis containing papillary villous projections consisting of fibrous cores, partially surfaced by a synovial-like lining. Based on these results, a metaplastic synovial cyst was diagnosed. The patient was referred to orthopaedic surgery for replacement to prevent recurrence, as the metal in the knee replacement was presumed the source of the cyst. The patient was then reassessed 3 months later, and he described resolution of his knee pain. Physical exam showed a well-healed linear scar. This patient's history and exam findings, along with the dermatopathology results, reflect the characteristic pattern in patients suffering from metaplastic synovial cysts. Prompt identification and subsequent removal can significantly improve patient's pain and ability to carry out daily activities.