Are synchronous and metachronous bilateral breast cancers different? An immunohistochemical analysis focused on cell cycle regulation

Introduction. The biology and pathomechanisms of bilateral breast cancers is not fully understood. We compared the morphological and immunohistochemical characteristics of primary tumors in patients with synchronous (sBBC) and metachronous bilateral breast cancers (mBBC), with special focus on cell cycle regulation and its correlation with markers determining intrinsic phenotype. Methods. Immunohistochemical expression of p16(Ink4A), p21(WAF1/CIP1), p27(Kip1), p53, cyclin A, cyclin B, cyclin D1, cyclin D3 and cyclin E was assessed in tissue microarrays containing primary breast tumor cores from 113 mBBC and 61 sBBC. Expression of these markers was correlated with tumor grade and expression of estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2) and Ki-67. Results. In univariate analysis, mBBC demonstrated higher expression of p16Ink4A (both cytoplasmic: p=0.002 and nuclear: p=0.014), cyclin A (p=0.024) and B (cytoplasmic; p=0.015). In multivariate analysis mBBC were associated with lower expression of p21: p=0.038 and higher cytoplasmic expression of cyclin B: p=0.019. Lower ER expression for all BBCs and mBBC, respectively, was associated with stronger p16 expression (cytoplasmic: both p<0.000001 and nuclear: p<0.000001, p=0.00002), p53: p<0.000001, p=0.000001, cyclin A: p=0.00002, p=0.00045, cyclin B (cytoplasmic: p=0.00037, 0.00015 and nuclear: both p=0.0004) and cyclin E: p=000003, p<0.000001, and weaker expression of p27: p=0.00003, p=0.0001 and cyclin D1: both p<0.000001; for sBBC some of these correlations were absent. Higher p27 score correlated with lower HER2 expression in sBBC: p=0.018, whereas higher HER2 expression was associated with higher p53: 0.024 and cyclin E: p=0.048 expression in all BBC and higher nuclear expression of cyclin B in sBBC: p=0.027. Higher Ki-67 expression was correlated with higher expression of p16 (cytoplasmic: p=0.000015, p=0.086, p=0.0002 and nuclear: p=0.000009, p=0.016, p=0.00003) in all subsets [all BBC, sBBC (nonsignificant for cytoplasmic score), mBBC, respectively], p21 (all BBC: p=0.05) and sBBC: p=0.017), p53 (all BBC: p=0.0003 and mBBC: p=0.0002), cyclin A: all p<0.000001, cyclin B (cytoplasmic: p<0.000001, p=0.004, p<0.000001, respectively and nuclear: p=0.0002, p=0.047, p=0.0026, respectively), cyclin D3 (all BBC: p=0.005 and mBBC: p=0.02) and cyclin E (all BBC: p<0.000001 and mBBC: p=0.000002), and lower expression of cyclin D1 (all BBC: p=0.046 and mBBC: p=0.035) and p27 (sBBC: p=0.048). Conclusion. Compared to sBBC, mBBC are characterized by lower expression of p21 and higher cytoplasmic expression of cyclin B, suggesting its more aggressive behavior. Correlations between cell-cycle regulation proteins and markers of breast cancer phenotype parallel those reported for unilateral breast cancer.