Histological intralesional heterogeneity of actinic keratoses relates to field cancerization

Histological heterogeneity within distinct actinic keratosis (AK) lesions has been described and might serve as an additional feature of AKs. We aimed to investigate and quantify the histological heterogeneity of AKs regarding different grading systems.

We assessed the histology of 3 mm biopsies of AK lesions located on the scalp or face. We documented basal proliferation (PRO I-III), histological grade (AK I-III) and determined the overall classification of each lesion.

Of the 305 lesions included, 48 (15.7 %) lesions were classified as AK I, 152 (49.8 %) as AK II and 105 (34.4 %) as AK III. 33 AKs (10.8 %) showed no basal proliferation, 94 (30.8 %) were graded as PRO I, 99 (32.5 %) as PRO II and 79 (25.9 %) as PRO III. One histological grade and basal growth pattern per lesion was observed in 94 (30.8 %) and 104 (34.1 %) cases respectively, two grades in 170 (55.7 %) and 168 (55.1 %) cases, and three grades in 41 (13.4 %) and 33 (10.8 %) cases (Chi-squared test, p < 0.0001).

By analogy with the clinical heterogeneity of field cancerization, AKs show a high histological grade heterogeneity even within small lesions. Variations in AK grading reflect the heterogeneity of the cancerization field and might serve as additional feature.