Incidence rates of carcinoma in situ increased at roughly twice the pace of invasive cutaneous squamous cell carcinoma over nearly two decades of national registry data from Denmark, according to a recent study.
In a nationwide Danish cohort of 109,787 histologically confirmed cases diagnosed between 2005 and 2023, researchers analyzed incidence trends of cutaneous squamous cell carcinoma (cSCC), carcinoma in situ, and keratoacanthoma (KA) using linked population-based registries. By 2023, age-standardized incidence rates for cSCC reached 131.6 per 100,000 person-years in male patients and 77.7 per 100,000 person-years in female patients, corresponding to estimated annual percentage increases of 2.6% and 3.1%, respectively. Carcinoma in situ demonstrated a steeper temporal rise, particularly after 2018, with estimated annual percentage changes of 6.4% in male patients and 5.8% in female patients and 2023 incidence rates of 89.4 and 78.6 per 100,000 person-years. In contrast, KA incidence declined over the study period, with estimated annual percentage decreases of 1.2% in male patients and 0.8% in female patients, reaching approximately 28 per 100,000 person-years in both sexes.
The researchers conducted a nationwide, population-based observational study using linked data from the Danish Pathology Registry and the Danish Cancer Registry, which provide near-complete coverage of the Danish population. The cohort included patients aged 20 years or older with a first-time diagnosis of cSCC, carcinoma in situ, or KA between January 1, 2005, and December 31, 2023. Case identification was based on standardized Systematized Nomenclature of Medicine morphology and topography codes, and inclusion was restricted to histologically confirmed lesions to ensure diagnostic accuracy. Patients could contribute to more than one diagnostic category; however, incidence analyses were based on first per-person diagnoses.
Incidence rates were calculated per 100,000 person-years using annual population counts as an approximation of person-time at risk and were age-standardized to the 2013 European Standard Population. Temporal trends were assessed using log-linear regression models to estimate annual percentage change, while Poisson regression models were applied for age-specific incidence analyses. Stratified analyses of age-standardized incidence rates by sex and anatomical site were performed, and age-specific incidence rates were calculated.
Site-specific analyses showed that cSCC and carcinoma in situ most frequently involved the face, scalp, and neck, particularly among male patients, whereas female patients had higher incidence rates on the lower limbs. Among patients aged 40 to 59 years, female patients showed higher incidence rates than male patients across all three keratinocyte neoplasms beginning around 2012. Incidence increased with advancing age across all neoplasm types, while trends among patients younger than 50 years were stable for cSCC and declined for KA.
Several limitations were noted. Restriction to histologically confirmed lesions likely resulted in underestimation of overall incidence, as some lesions may be managed without biopsy. Temporal changes in diagnostic practices, biopsy thresholds, and surveillance intensity may have contributed to observed increases in cSCC and carcinoma in situ. In addition, the use of first per-person diagnoses does not capture the full tumor burden among patients with multiple lesions, and residual confounding by factors such as immunosuppression status or ethnicity could not be fully addressed.
Disclosures can be found in the study.
Source: JAMA Dermatology
