Cyclin D1 protein overexpression and gene amplification in benign breast tissue and breast cancer risk

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Abstract
Cyclin D1 amplification and/or protein overexpression have been observed not only in breast cancer but also in the putative early stages of breast neoplasia. In a case–control study nested within a cohort of 4888 women, we investigated whether the occurrence of cyclin D1 gene amplification and/or protein overexpression in benign breast tissue might identify women at increased risk of subsequent breast cancer development. Cases were 92 women with a histological diagnosis of benign breast disease who subsequently developed breast cancer. Five controls (women with benign breast disease who had not developed breast cancer by the date of diagnosis of the corresponding case) were selected randomly for each case from those non-cases available within strata defined by screening centre, National Breast Screening Study (NBSS) study arm, year of birth and age at diagnosis of benign breast disease. Paraffin blocks of benign tissue were suitable for immunostaining for 71 cases and 293 controls. Sufficient DNA for analysis was obtained from a total of 356 subjects (69 cases, 287 controls). The benign breast tissues and breast cancers were immunostained for cyclin D1 and also analysed for the presence of cyclin D1 gene amplification by differential polymerase chain reaction (PCR). Fifteen cases and 60 controls showed evidence of cyclin D1 immunostaining, and 12 cases and 29 controls showed cyclin D1 gene amplification. There was essentially no association between cyclin D1 protein overexpression in benign breast tissue and risk of subsequent breast cancer (adjusted odds ratio (OR) 1.06; 95% confidence interval (CI) 0.56–2.02). After adjustment for potential confounding, there was a statistically non-significant 40% increase in risk of breast cancer in association with cyclin D1 gene amplification (adjusted OR 1.41; 95% CI 0.62–3.22). As multiple genetic changes are required to develop breast cancer, it may not be until the cascade of molecular alterations leading to breast cancer development is understood that identification of biomarkers of breast cancer risk will be possible.