Expression of G1/S Phase Checkpoint Proteins in Breast Carcinoma: Relationship to Clinicopathologic Factors andSurvival Rate

Lee, Mi Ja

Abstract

The retinoblastoma protein (pRb)/cyclin D1/ p16 pathway plays a critical role in controlling the progression from G1 to S phase of the cell cycle. Abnormal expression of the individual components of the pathway has been reported in many human cancers, including the breast. Our aim was to investigate the role of this pathway in tumorigenesis and tumor progression, and to evaluate the value of these oncoproteins as potential prognostic factors in breast cancer.
MATERIALS AND METHODS
We examined the significance of the p16, pRb, and cyclin D1 expression in 128 cases of invasive breast carcinomas using immunohistochemistry on formalin fixed, paraffin sections. The results correlated with the survival rate and clinicopathologic variables, including age, histologic grade, lymph node status, tumor size, estrogen receptor (ER) and progesterone receptor (PR) content. The negative finding for nuclear staining for pRb and p16 were defined as abnormal.
RESULTS
Abnormal expression of the p16 and pRb were seen in 21% and 43% of tumors, respectively. There was a significant inverse relationship between the p16 and pRb expressions. There was no association between the p16 staining and any other parameters, including survival rate, cyclin D1, or clinicopathologic variables. Surprisingly, there was a trend for pRb positive tumors to be grade III ductal carcinomas. Cyclin D1 positivity was noted in 46% of cases. The expression of cyclin D1 protein was significantly higher in lower histologic grades, and with higher ER and PR expressions.
CONCLUSION
These findings suggest the p16 may be negatively regulated by the pRb, and that cyclin D1 is involved in the tumor progression in well-differentiated tumors and could be an ER and PR related protein. In a Cox multivariate analysis, the p16, pRb, and cyclin D1 were not independent predictors of patient outcome.