p27^Kip1 is a member of the Cip/Kip family of cyclin-dependent kinase inhibitors. It binds to a variety of cyclin/CDK complexes, inhibits kinase activity and blocks the cell cycle as a negative regulator. Reduced p27^Kip1 expression has been reported to be a significant predictor of poor survival in numerous human breast cancers. We executed p27^Kip1 protein assay in primary breast cancer and compared these result with known prognostic parameters.

Immunohistochemical assay was performed on tissue microarrays from 183 patients with breast cancer to evaluate the biologic and clinical significance of p27^Kip1 expression.

Decreased p27^Kip1 expression was significantly associated with clinical stage (P=0.027), low nuclear grade (P<0.001), high histologic grade (P<0.001), high score mitotic index (P<0.001), increased Ki67 labeled index (P=0.006) and negative estrogen receptor status (P=0.0024). In survival analysis, p27^Kip1 was useful to predict diseasefree survival (P=0.0106) and overall survival (P=0.0154) of the patient after surgery followed by chemotherapy or radiation therapy.

Reduced expression of p27^Kip1 protein was associated with biologically aggressive phenotype of breast cancer and was an useful to predict patient outcome.