The burden of cutaneous adnexal carcinomas and the risk of associated squamous cell carcinoma: a population‐based study.

Summary: Background: Recent studies have shown an increasing incidence of cutaneous adnexal carcinomas (CACs). Objectives: The aim of our study was to evaluate incidence and survival for cases of CACs and investigate their association with other skin neoplasms. Methods: We conducted a population‐based study. Data on incident cases of CACs were obtained from the Tuscany Cancer Registry between 1985 and 2010. In order to determine whether the occurrence of squamous cell carcinoma (SCC) among patients with CAC is higher or lower than expected in the general population, the standardized incidence ratio (SIR) was calculated. Results: A total of 242 patients with CAC were observed; the age‐standardized incidence rate was 3·8 cases per million person‐years. From 1997 to 2010 crude incidence rates increased by 159%. Age‐specific incidence was higher in men over 80 years old than in women of the same age and younger individuals. Carcinomas of sweat gland origin prevailed; the most common histotype was porocarcinoma and the most frequently affected site was the head/neck. Overall, 88% of CACs were diagnosed at a localized stage. The 5‐year overall survival and disease‐specific survival rates were 59% [95% confidence interval (CI) 53–65] and 94% (95% CI 91–98), respectively. In the observation cohort, the number of SCCs was significantly higher than expected as the SIR was calculated to be 33·7 (P < 0·001). Conclusions: Increasing incidence warrants awareness and early diagnosis of CACs. Increased SCC incidence among patients with these tumours highlights the relevance of careful skin examination and follow‐up. What's already known about this topic? Cutaneous adnexal carcinomas (CACs) are rare tumours, but their incidence is increasing.The rarity of these tumours has made it difficult to gain sufficient clinicopathological experience regarding the diagnosis and treatment of CACs.CACs can be a diagnostic challenge owing to mostly nonspecific clinical presentation and histopathological variety that often requires specific expertise for a definite diagnosis. What does this study add? CAC incidence increased from 2·5 per million person‐years in 1985–87 to 19 per million person‐years in 2009–10; from 1997 the incidence has constantly increased, rising to 159% in 2010.In patients with CAC, the risk of squamous cell carcinoma is 34 times higher than in the general population.Considering demographic evolution with a progressively ageing population and higher incidence of CACs among the elderly, it is reasonable to expect a further increase in the future. Respond to this article Linked Comment:Andersen. Br J Dermatol 2019; 180:453–454. Plain language summary available online [ABSTRACT FROM AUTHOR]