Heterogeneous Chromosomal Aberrations in Intraductal Breast Lesions Adjacent to Invasive Carcinoma

There is evidence that breast cancer is a heterogeneous disease phenotypically as well as molecular biologically. So far, heterogeneity on the molecular biological level has not been investigated in potential precursor lesions, such as ductal hyperplasia (DH) and ductal carcinoma in situ (DCIS). In this study we applied comparative genomic hybridization (CGH) to formalin‐fixed, paraffin‐embedded breast tissue with DH and DCIS, adjacent to invasive ductal carcinoma (IDC), to screen these potential precursor lesions for whole genomic chromosomal imbalances. Laser‐microdissection was used to select pure cell populations from the sections. Isolated DNA was amplified by degenerate oligonucleotide primed PCR (DOP‐PCR) and further processed for CGH analysis. Investigating multiple samples (n=25) from four patients we found an average of 5.6 ± 0.9 (mean ± SEM) chromosomal imbalances already present in DH. In the twelve DCIS lesions an average of 10.8 (±0.9) aberrations was identified with 14.8 (±0.8) aberrations in the four adjacent IDC lesions. The increasing number of chromosomal changes in parallel with the histopathological sequence corroborate the hypothesis, that the carcinomas may have developed through a sequential progression from normal to proliferative epithelium and eventually into carcinoma. However, heterogeneous results were identified in the multiple samples per entity from the same patient, demonstrated mainly in the DCIS samples in the chromosomal regions 6p, 9p, 11q, 16p and 17q, in the DH samples by 3p, 16p and 17q. This heterogeneous findings were most pronounced within the DH and was less in the DCIS and IDC samples. The only aberration consistently found in all samples – even in all DH samples – was amplification of the 20q13 region. Our results demonstrate, that the applied combination of laser‐microdissection, DOP‐PCR and CGH, may serve to analyse breast carcinogenesis pathways in suitable histological material. However, so far, it is unclear how to handle heterogeneous results and these make identification of relevant changes more difficult. Setting a threshold and valuating only those chromosomal changes which are present in a majority of samples may be one possibility. This involves however, the risk that infrequent but possibly significant aberrations may be missed. Figures on http://www.esacp.org/acp/2000/20‐1/aubele.htm.