Abstract: Objective To explore the difference of apoptosis and cellular proliferation between keratoacanthoma (KA) and cutaneous squamous cell carcinoma (SCC). Methods Programmed cell death (apoptosis) was identified by an in situ terminal deoxynucleotidyl transferas (TdT)-mediated dUTP-biotin nick and labelling staining (TUNEL) in 20 KA and 25 SCC cases. Expression of nuclear antigen Ki-67 and two protooncogenes, bcl-2 and bax, recently recognized to be involved in apoptosis, were detected by immunohistochemical technique. Results Apoptotic cells distributed densely at the cancer nests of KA and well differentiated SCC or diffusely in poorly differentiated SCC. The percentages of apoptotic cells were significantly higher in KA (48.83%) than those in SCC (26.08%)(t=2.274,P=0.028). The densities of Ki-67 staining were greater in SCC than those in KA. The percentages of cellular proliferation were 9.03% in KA and 27.20% in SCC(t=3.281,P=0.002). In SCC, the poorer the differentiation, the less the apoptosis, and the higher proliferative activity. Weakly staining bcl-2 antigen was observed in KA (6/20) and SCC (6/25)(P>0.05).Bax staining was positive in all cases,and stronger in KA than that in SCC (U=2.489,P=0.013). There were a positive correlation between apoptosis and intensity of bax expression and a negative correlation between apoptosis and intensity of bcl-2 expression. Conclusion It is suggested that there are similar biological characteristics in cellular apoptosis and gene regulation of apoptosis in KA and SCC. However, proliferative activity in SCC was higher than that in KA.

Key words: Keratoacanthoma, Carcinoma,squamous cell, Apoptosis