Clinical Olsen Grading Does Not Reflect Basal Growth in Actinic Keratoses: Two-Center Retrospective Analysis.

Background/Objectives: Actinic keratosis (AK) is a precancerous lesion that may progress into cutaneous cancer. However, the progression potential of individual lesions remains unpredictable. The histological basal proliferation pattern of AKs may serve as a risk marker for progression, yet it cannot be assessed clinically. The objective was to evaluate whether Olsen grading (hyperkeratosis of AKs) and pain as clinical markers correlate with the histological basal proliferation (PRO) and different histological aspects. Methods: In this retrospective two-center study, 380 clinically diagnosed AKs were graded according to the clinical Olsen classification (I-III) and assessed for pain upon palpation. Histologically, they were classified based on their basal- (PRO I-III) and upward-directed (AK I-III) growth patterns, and additional histopathological features, such as acantholysis, were documented. Results: Olsen grading showed weak correlation with the PRO classification (Spearman's rho = 0.136, p = 0.008), with exact agreement of 36.3% (κ = 0.07). Pain was significantly associated with higher PRO grades (p = 0.005) and acantholysis (p = 0.023) but not with Olsen grades or upward-directed growth (AK I-III). Conclusions: Olsen grading does not allow reliable prediction of basal proliferation patterns in AKs. Its use as a clinical severity scale may suggest progression relevance; however, no substantiated association with histological indicators of transformation could be demonstrated in this study. The presence of pain, however, correlated with high PRO grades and the presence of acantholysis.