Cyclin D1 gene amplification and protein expression in benign breast disease and breast carcinoma

Cyclin D1 plays a critical role in regulating cell-cycle progression. Gene amplification and protein overexpression of cyclin D1 have been detected in breast cancer but little is known concerning whether these changes occur in normal breast tissue and in breast lesions associated with increased risk of development of invasive breast cancer. We looked for cyclin D1 gene amplification and protein overexpression in 30 cases of benign breast disease (16 epithelial hyperplasias without atypia and 14 atypical ductal hyperplasias) and 18 ductal carcinomas in situ by use of differential PCR and immunohistochemical staining. We compared the resulting frequencies to those in 15 cases of normal breast tissue and 17 invasive ductal carcinomas. We found cyclin D1 gene amplification in 15% of those with normal breast tissue, 19% of those with epithelial hyperplasia without atypia, 27% of those with atypical ductal hyperplasia, 35% of those with ductal carcinoma in situ, and 25% of those with invasive ductal carcinoma; corresponding figures for protein overexpression were 13, 13, 57, 50, and 64%. These results suggest that cyclin D1 amplification and protein overexpression can occur before histologic alterations are seen but that the frequencies of these changes are higher in histologic lesions with cellular atypia (atypical hyperplasia and ductal carcinoma in situ), reaching frequencies similar to those observed in invasive carcinoma.