Prevalence of extramammary Paget's disease in urban China: a population-based study.

BACKGROUND: Extramammary Paget's disease (EMPD) is an intraepithelial adenocarcinoma. The chronic relapsing clinical course and unbearable clinical symptoms of extramammary Paget's disease usually result in a markedly diminished quality of life. No national data are available on descriptive epidemiology of EMPD in China, the most populous country over the world. This population-based study aimed to estimate the prevalence and associated sex and age patterns of EMPD in China. METHODS: This study was conducted using data from China's Urban Employee Basic Medical Insurance and Urban Resident Basic Medical Insurance, covering approximately 0.43 billion Chinese urban residents in 2016. Patients with EMPD were identified based on the diagnostic names and codes in claim data. RESULTS: A total of 53 males and 31 females with EMPD were found. The crude prevalence in 2016 was 0.04 per 100,000 population [95% confidence interval (CI) 0.02-0.06], ranging from 0.01 (95% CI 0.00-0.02) in North or Northeast China to 0.08 (95% CI 0.03-0.16) in Southwest China. The rate was higher in males (0.05, 95% CI 0.03-0.08) compared with females (0.03, 95% CI 0.02-0.05). The mean age of patients was 65.87 (standard deviation: 14.21) years, with the peak prevalence appeared in patients aged 70-79 (0.28, 95% CI 0.16-0.42). CONCLUSIONS: The prevalence of EMPD was markedly lower than those in the United States and Europe, and varied across regions in China. Chinese patients were much younger, with significant male predominance. Further studies are warranted to examine potential pathophysiologic mechanism.