(A-E) AIM2 expression was determined by IHC of TMAs containing normal human skin (n=15), actinic keratosis (AK) (n=71), cSCCs in situ (cSCCIS) (n=60) and sporadic cSCCs (n=81). In sporadic, UV-induced human cSCC tumor cell-specific cytoplasmic and perinuclear localization of AIM2 was detected and the expression level was mainly strong (+++) (D, E) or moderate (++). In cSCCIS, AIM2 expression level was moderate (++) (C) in the majority of sections. In AK, AIM2 expression was mainly weak (+) (B). AIM2 expression was absent (−) or weak (+) (A) in normal skin samples. (F) Tumor cell-specific cytoplasmic and perinuclear expression of AIM2 was detected in cSCCs of OTRs. Scale bar=50 μm. (G) AIM2 expression level was significantly stronger in sporadic cSCCs compared with cSCCIS, AK and normal skin. (H) In OTR derived tissues, AIM2 expression was significantly more abundant in cSCC (n=57) compared with cSCCIS (n=59) and AK (n=58). (*P<0.05, *** P<0.001; Fisher's exact test).