“…The histopathological criteria for each stage of KA were based on various textbooks and reviews, as described in detail later in this manuscript. 2 -4,9,12,31 -34 During the process of this careful selection, we eliminated the following cases: (i) 'KA-like SCCs (five lesions)' 35 -37 that histopathologically resembled KA but had an eccentric architecture and prominent atypical cytological features, (ii) 'infundibular and infundibulocystic SCCs (11 lesions)' which have been described elsewhere, 38 and diagnostically challenging cases (six lesions) with regard to whether the lesion was a very early stage of KA or infundibular and infundibulocystic SCC, (iii) 'KA associated with SCC/KA with malignant transformation (four lesions)', 6,7,37 (iv) crateriform SCC arisen from actinic keratosis (four lesions), 6,37 and (v) crateriform Bowen's disease (one lesion). 37 After this careful selection, a total of 67 'pure' KAs, including 16 early or proliferative stage lesions, 43 well-developed stage lesions, five regressing stage lesions and three regressed stage lesions, were chosen from the 98 'KA-like lesions'.…”