Cutaneous squamous cell carcinomas are associated with basal proliferating actinic keratoses

Abstract

Background

In addition to the extent of atypical keratinocytes throughout the epidermis, actinic keratoses (AKs) are histologically characterized by downward directed basal layer expansion. It is not known if this growth pattern correlates with the risk of developing invasive squamous cell carcinoma (iSCC).

Objective

To characterize the prevalence of downward directed basal layer expansion of AKs adjacent to iSCC.

Methods

The epidermis overlying and adjacent to iSCCs was assessed histologically. We determined the histological grade (AKI-III), basal growth pattern (PROI-III) and accompanying parameters such as adnexal involvement.

Results

Of 307 lesions, 52.4% of AKs were histologically classified as AKI, 38.1% as AKII, and 6.8% as AKIII (chi-squared; P<0.0001). 2.6% of adjacent epidermis did not show any atypical keratinocytes. The epidermis adjacent to iSCCs was classified as having a PROI basal growth pattern in 25.7%, PROII in 31.9%, and PROIII in 39.4% cases. 2.9% of AKs showed no basal growth (chi-squared; P<0.0001).118 (48.8%) AKs showed extension into adnexal structures. These AKs were graded as PROI in 18.6%, PROII in 30.5%, and PROIII in 50.8%. The epidermis above iSCCs could only be assessed for upwards directed growth and showed no significant differences in the three AK grades (P=0.4211).

Conclusions

Basal proliferative AKs as well as atypical keratinocytes restricted to the lower third of the epidermis are most commonly seen adjacent to iSCC with less evidence for full thickness epidermal dysplasia. Our study supports the important role of dysplastic keratinocytes in the epidermal basal layer and their potential association with iSCC.

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