An increasing incidence of the keratinocyte skin cancers cutaneous squamous cell carcinoma (cSCC) and carcinoma in situ (CIS), with notable differences by sex, age and body location, has been revealed through an analysis of registry data spanning over two decades, emphasising the need for surveillance and person-centred care.

The nationwide Danish cohort study, published in JAMA Dermatology, sought to estimate incidence rates and temporal trends in first-time diagnoses of keratinocyte neoplasms using data from the Danish Pathology Registry and the Danish Cancer Registry.

The analysis included individuals aged 20 years or older diagnosed with one of three keratinocyte neoplasms between 2005 and 2023: cSCC, CIS or keratoacanthoma.

Overall, 109,787 histologically confirmed cases were identified among 95,352 individuals with a first diagnosis of cSCC (54,563 cases), CIS (31,712 cases), or keratoacanthoma (23,512 cases). Approximately half of the cohort were men (55,891; 50.9%).

The median age at diagnosis of a first-time keratinocyte neoplasm ranged from the early 70s for keratoacanthoma (73 years for men and 72 years for women) to the late 70s for cSCC and CIS (both sexes 77 years and 76 years, respectively).

The researchers calculated age-standardised incidence rates (ASIRs) per 100,000 person-years and assessed temporal trends using estimated annual percentage change.

Incidence trends of keratinocyte neoplasms

Across the study period, the incidence of cSCC increased steadily in both sexes. ASIRs rose by an estimated 2.6% per year among men (95% CI 2.2–3.0) and 3.1% per year among women (95% CI 2.6–3.6).

By 2023, incidence was 131.6 cases per 100,000 person-years among men and 77.7 cases per 100,000 person-years among women.

CIS incidence increased even more sharply. Annual increases were estimated at 6.4% in men (95% CI 5.0–7.8) and 5.8% in women (95% CI 4.7–7.0), reaching 89.4 and 78.6 cases per 100,000 person-years, respectively, by 2023. Much of this rise occurred after 2018, particularly among individuals aged 50 years or older.

In contrast, keratoacanthoma incidence declined slightly during the same period. The estimated annual percentage change was −1.2% in men (95% CI −1.9 to −0.5) and −0.8% in women (95% CI −1.5 to −0.1), with rates of 28.6 and 27.6 per 100,000 person-years, respectively, in 2023.

Sex- and site-specific patterns

When it came to keratinocyte skin cancers, men experienced a higher incidence of cSCC and CIS on the face, scalp and neck, whereas women showed higher rates on the lower limbs. For example, cSCC incidence on the lower limbs reached 12.32 per 100,000 person-years in women compared with 7.63 in men.

In the 40-59-year age group, women had higher incidence rates than men across all three tumour types. However, among older age groups, particularly those aged 60 years and above, rates remained substantially higher in men.

Encouragingly, incidence trends of cSCC and keratoacanthoma among individuals younger than 50 years were stable or declining, suggesting that prevention initiatives, such as public health campaigns promoting sun protection, might be starting to have an effect after previous doubts.

According to the authors, these findings align with cumulative ultraviolet radiation exposure being a major risk factor, although behavioural differences between sexes may also play a role.

The increase in CIS diagnoses after 2018 may also partly result from improved histopathological classification following updated World Health Organization guidelines and heightened clinical detection, they added.

Guiding future keratinocyte skin cancer surveillance efforts

Several limitations should be considered when interpreting the findings. Although the nationwide registries provide high-quality coverage, the study included only histologically confirmed cases, meaning incidence may be underestimated if lesions were treated without biopsy. Trends may also reflect changes in biopsy practices or increased clinical surveillance.

Additionally, tumour-based incidence was not captured because only first diagnoses per person were analysed. Residual confounding by factors such as ethnicity, transplant status or immunosuppression could also not be fully assessed.

The findings highlight the growing impact of keratinocyte skin cancers and the ongoing relevance to public health. This, along with epidemiological patterns could guide future surveillance efforts and promote more person-focused approaches to dermatological diagnosis and treatment, the authors concluded.

Reference
Duffau K et al. Incidence Trends of Cutaneous Squamous Cell Carcinoma, Carcinoma In Situ, and Keratoacanthoma By Sex, Age and Anatomical Site. JAMA Dermatol 2026;Jan 28:e255700.