Assessment of Incidence Rate and Risk Factors for Keratoacanthoma Among Residents of Queensland, Australia

Importance

Keratoacanthoma (KA) is a common and generally benign keratinocyte skin tumor. Reports of the incidence rates of KA are scant. In addition, the risk factors for KA are not well understood, although associations with UV radiation exposure and older age have been described.

Objective

To investigate the incidence rate of KA and the risk factors for developing KA.

Design, Setting, and Participants

The study included data from 40 438 of 193 344 randomly selected residents of Queensland, Australia, who participated in the QSkin Sun and Health (QSkin) prospective population-based cohort study. All participants completed a baseline survey between 2010 and 2011 and were ages 40 to 69 years at baseline. Histopathologic reports of KA were prospectively collected until June 30, 2014, through data linkage with pathologic records. Cox proportional hazards models were used to identify risk factors associated with KA while controlling for potential confounding variables. Data were analyzed from January 2 to April 8, 2020.

Exposures

Demographic characteristics, phenotypes, UV radiation exposure, medical history, and lifestyle.

Results

Among 40 438 participants (mean [SD] age, 56 [8] years; 18 240 men [45.1%]), 596 individuals (mean [SD] age, 62 [6] years; 349 men [58.6%]) developed 776 KA tumors during a median follow-up period of 3.0 years (interquartile range, 2.8-3.3 years). The person-based age-standardized incidence rate for KA in the age-restricted cohort was 409 individuals per 100 000 person-years (based on the 2001 Australian population). Risk factors after adjustment for potential confounders were older age (age ≥60 years vs age <50 years; hazard ratio [HR], 6.38; 95% CI, 4.65-8.75), male sex (HR, 1.56; 95% CI, 1.33-1.84), fair skin (vs olive, dark, or black skin; HR, 3.42; 95% CI, 1.66-7.04), inability to tan (vs ability to tan deeply; HR, 1.69; 95% CI, 1.19-2.40), previous excisions of keratinocyte cancers (ever had an excision vs never had an excision; HR, 6.28; 95% CI, 5.03-7.83), current smoking (vs never smoking, HR, 2.02; 95% CI, 1.59-2.57), and high alcohol use (≥14 alcoholic drinks per week vs no alcoholic drinks per week; HR, 1.42; 95% CI, 1.09-1.86).

Conclusions and Relevance

This is, to date, the first large prospective population-based study to report the incidence rate and risk factors for KA. The high person-based incidence rate (409 individuals per 100 000 person-years) highlights the substantial burden of KA in Queensland, Australia. Furthermore, the study's findings suggest that older age (≥60 years), male sex, UV radiation-sensitive phenotypes, indications of high sun exposure (eg, previous keratinocyte cancer excisions), smoking, and high alcohol use are independent risk factors for the development of KA.

Diagnosis and Follow-Up of Keratoacanthoma-Like Lesions: Clinical-Histologic Study of 43 Cases

Background:

Keratoacanthoma (KA) is easily confused with squamous cell carcinoma (SCC) on a clinical or a histopathologic basis. However, KA undergoes spontaneous regression, whereas SCC does not.

Objective:

Our objective was to study the histopathologic features associated with clinical regression in KA-like lesions to support the therapeutic option.

Methods:

Forty-three biopsies of KA-like lesions were taken at patient admission. One month later, surgical excision was performed in 18 growing lesions. Regressing lesions were left untreated. Classic histopathologic features and diagnosis were blindly recorded in both biopsies and surgical specimens.

Results:

On a clinical and a histologic basis, 32 lesions were assessed as KA and 11 as SCC. Features that indicated malignancy were observed in both groups, but the probability of SCC was 31 times higher in tumors with five or more of such features. Several of the histologically atypical lesions were found to regress.

Conclusion:

SCCs and KAs have more pathologic similarities than differences, especially in the proliferative phase. The combination of the most useful features did not allow the nosologic diagnosis in difficult cases but helped. Differential diagnosis was easier to determine after the 1-month follow up. Complete surgical excision should be indicated in nonregressing and growing lesions.