Understanding Biological Rationale For Specific Activity Of Cdk1 And Cdk2 As A Prognostic Marker Of Breast Cancer Recurrence

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO Background: Cyclin-dependent kinases (CDKs) are the prime regulators of cell cycle. We have reported that specific activity of CDK1 (CDK1SA) and CDK2SA are useful to predict postoperative recurrence of breast cancer patient. However, the procedure to set the cutoffs was complicated and intuitive. Moreover, the biological meaning of CDK-parameters was not clarified in vivo. The aims of the present study are 1) to assess the biological significance of CDK-parameters and 2) to define statistically rationalized recurrence-predicting procedure. Experimental procedure: Tumor tissues were obtained from patients with primary invasive breast cancer who did not receive chemotherapy but hormonal therapy. Expressions and kinase activities of CDKs were measured using frozen tissue. Immunohisotchemical analysis was performed using formalin-fixed paraffin-embedded tissue. Chromosomal instability was examined by FISH. Summary: Since it was shown that the recurrence for breast cancer recurrence can be predicted based on CDK1SA, CDK2SA and relative CDK2SA to CDK1SA (CDK2SA/CDK1SA-ratio), we first examined whether these CDK-parameters were correlated with conventional prognostic markers such as Ki-67, mitotic index and nuclear grade. As expected, CDK2SA/CDK1SA-ratio and CDK2SA significantly associated with markers reflecting tumor growth (Ki-67 and mitotic index: p<0.01) (N=25). In addition, it was found that CDK1SA showed a significant correlation with nuclear grade (p<0.01), rather than the growth indicators. More interestingly, increase in number of centrosome along with CDK1SA (r=0.83, p<0.01) was observed in immunohistochemically p53-positive cases, suggesting that CDK1SA reflects disruption in cell-cycle checkpoint, whereas chromosomal instability did not have apparent correlation with CDK-parameters. Based on these findings, we then defined a procedure to evaluate the risk for recurrence. When distribution of CDK-parameters of cases were examined (N=284), rate of recurrence monotonically increased along with relative CDK2SA/CDK1SA-ratio as well as CDK1SA. These correlations were approximated to logistic curves: Eq1 = 0.25 / (1 + Exp(-(x - 1.0) x 6), x = log(CDK2SA/CDK1SA), and Eq2 = 0.20 / (1 + Exp(-(y - 1.6) x 7), y = log(CDK1S/A). A risk score (RS) was then defined multiplying Eq.1 and Eq.2. The robustness of RS was confirmed by the followings; 1) risk for recurrence increases along with RS and 2) RS significantly associates with the growth indicators (p<0.01). Conclusion: CDK-parameters were suggested to reflect disruption in cell-cycle checkpoints, as well as proliferative property of cancer cells. A scoring procedure to predict the recurrence according to CDK1SA and CDK2SA was successfully defined by statistical approach. RS-based recurrence prediction analysis should be validated with larger sample size. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 5556.