Cyclin D1 overexpression in invasive breast cancers: correlation with cyclin-dependent kinase 4 and oestrogen receptor overexpression, and lack of correlation with mitotic activity

Background: Cyclin D1 (CCND1) and its catalytic partner cyclin-dependent ki nase 4 (cdk4) are known to play important roles in the G1/S check point of the cell cycle, and CCND1 overexpression has been reported to correlate wit h progression and prognosis of breast cancers. Oestrogen receptor (ER) leve ls determine the proliferative response to oestrogen by regulating binding. It has been postulated that CCND1 and cdk4 exert effects on mammary carcin ogenesis in co-operation with ER. Patients and methods: CCND1 and cdk4, ove rexpression in 117 breast cancer cases with long-term follow-up were invest igated by means of immunohistochemistry and differential polymerase chain r eaction (PCR), using formalin-fixed and paraffin-embedded samples, and comp ared with ER status and mitotic indices. Additional Western blotting and re verse transcription (RT)/PCR/Southern blot hybridization were performed for 4 breast cancer cell lines and 15 fresh-frozen breast cancer samples to co nfirm CCND1 and cdk4 data. Results: Immunohistochemically 27 cases were CCN D1-positive (23.0%), and CCND1 amplification was evident in 21 (21/86; 24.4 %). The two methods in combination demonstrated 37 cases (31.6%) to be posi tive for CCND1 overexpression. Western blotting revealed 60% of samples of fresh tissue to overexpress CCND1, corresponding well with the results of R T-PCR. There was thus a strong discrepancy between results for paraffin blo ck and fresh samples, probably because of the short life of CCND1. In the c ase of cdk4, the respective percentages for positive cases were 54.7% and 7 3%. CCND1 and cdk4 overexpression (P < 0.0001), and CCND1 and ER positivity (P = 0.0128) correlated. In addition, samples overexpressing CCND1, cdk4 a nd ER tended to have slightly lower proliferative activity than samples whe re these were absent. However, no association with clinicopathological para meters was evident, cdk4 overexpression had no linkage with ER status or cl inicopathological status. Neither CCND1 nor cdk4 expression affected progno sis. Conclusion: CCND1 overexpression does not correlate with cancer progre ssion or prognosis or with mitotic activity. The results may suggest that a n excess accumulation of CCND1 in breast cancer cells tends to suppress ent ry into the S phase of the cell cycle.