Fernandez-Figueras MT, et al. - The relationship between follicular extension of atypical keratinocytes in an actinic keratosis (AK) and the development of iSCC from the follicular wall was evaluated herein. Experts correlated the depth of follicular extension with the depth invasion of iSCC. They also examined the differences between the differentiated and classical pathways of iSCC. Irrespective of the pathway of origin, the depth of follicular extension of atypical keratinocytes in an AK associated with the development of depth of invasion of the related iSCC. Since follicular extension likely accounts for a significant proportion of recurrent AK and the development of iSCC after superficial treatment modalities, therefore noting the presence and the depth of follicular extension when diagnosing an AK was important.