Chromosomal Aneuploidy in Proliferative Breast Disease

Although some forms of proliferative breast disease have been associated with increased risk of breast cancer, substantial confirmatory evidence that the lesions are biologically premalignant has not been presented. Our intent was to identify cytogenetic aberrations in proliferative breast disease using fluorescence in situ hybridization probes selected for their relationship to aberrations previously reported in breast cancer. Application of fluorescence in situ hybridization techniques to paraffin tissue sections using pericentromeric probes for chromosomes 1, 16, 17, 18, and X revealed chromosome aneuploidy in proliferative and malignant lesions of the breast. Sectioning artifact that may result in nuclear truncation was controlled by establishing expected baseline frequencies for gain and loss in normal tissues from the same breast. Localization of chromosomal aberrations to proliferative breast disease lesions with concomitant retention of a normal chromosome complement in corresponding normal breast tissues indicates biologic significance of the results. The similarities of losses involving chromosomes 16, 17, and 18 in hyperplastic lesions and in malignant breast lesions suggest that some hyperplasias may be part of a sequence of progression to malignancy in breast cancer. Gains of chromosome 1 in both in situ and invasive carcinoma are consistent with reports of polysomy 1q as a common cytogenetic change in breast cancer. Its localization to advanced lesions suggests that this trisomy is probably not the initial cytogenetic change in breast cancer tumorigenesis.