To investigate whether the connection of p27

Kip1

to S-phase kinase-associated protein 2 (Skp2) plays an oncogenic role in intraductal proliferative lesions of the breast. Methods Here we investigated the mechanism involved in association of Skp2’s degradation of p27

Kip1

with the breast carcinogenesis by immunohistochemical method through detection of Skp2 and p27

Kip1

protein levels in 120 paraffin-embedded tissues of intraductal proliferative lesions including usual ductal hyperplasia (UDH

n=30)

atypical ductal hyperplasia (n=30)

flat epithelial atypia (FEA

n=30)

and ductal carcinoma in situ (DCIS

n=30).Moreover

the expression status of Skp2 and p27

Kip1

in 30 cases of the normal breast paraffin-embedded tissues were explored. Results The DCIS group was with the highest Skp2 level and the lowest p27

Kip1

level

and the UDH group was with the lowest Skp2 level and the highest p27

Kip1

level.Both Skp2 and p27

Kip1

levels in the DCIS group were significantly different from those in the UDH group (all P

<

0.01).The levels of Skp2 and p27

Kip1

in the FEA group were significantly different from both the DCIS and UDH groups (all P

<

0.05).p27

Kip1

was negatively correlated with Skp2 in both the UDH group (r=-0.629

P=0.026) and DCIS group (r=-0.893

P=0.000). Conclusion Overexpression of Skp2 might be the mechanism underlying p27

Kip1

over degradation.