Aneuploidy for chromosome 1 and overall DNA content in benign and malignant breast disease

Genomic Changes in Normal Breast Tissue in Women at Normal Risk or at High Risk for Breast Cancer

Sporadic breast cancer develops through the accumulation of molecular abnormalities in normal breast tissue, resulting from exposure to estrogens and other carcinogens beginning at adolescence and continuing throughout life. These molecular changes may take a variety of forms, including numerical and structural chromosomal abnormalities, epigenetic changes, and gene expression alterations. To characterize these abnormalities, a review of the literature has been conducted to define the molecular changes in each of the above major genomic categories in normal breast tissue considered to be either at normal risk or at high risk for sporadic breast cancer. This review indicates that normal risk breast tissues (such as reduction mammoplasty) contain evidence of early breast carcinogenesis including loss of heterozygosity, DNA methylation of tumor suppressor and other genes, and telomere shortening. In normal tissues at high risk for breast cancer (such as normal breast tissue adjacent to breast cancer or the contralateral breast), these changes persist, and are increased and accompanied by aneuploidy, increased genomic instability, a wide range of gene expression differences, development of large cancerized fields, and increased proliferation. These changes are consistent with early and long-standing exposure to carcinogens, especially estrogens. A model for the breast carcinogenic pathway in normal risk and high-risk breast tissues is proposed. These findings should clarify our understanding of breast carcinogenesis in normal breast tissue and promote development of improved methods for risk assessment and breast cancer prevention in women.

Relation between deletion of chromosome 1p36 and DNA ploidy in breast carcinoma: an interphase cytogenetic study

Aims-To investigate whether deletion of the 1p36 region of chromosome 1 is independent of DNA ploidy in breast cancer cells.Methods-Preparations of nuclei from 64 fresh primary breast tumours were studied using dual target fluorescence in situ hybridisation (FISH) combining probes specific for the 1q12 (pUC 1.77) and 1p36 (1p-79) regions of chromosome 1. Signals were counted in 100-300 nuclei and the percentage of cells showing fewer p1-79 than pUC 1.77 signals was measured in each sample. DNA ploidy was investigated by cytofluorimetry in 55 tumour samples.Results-Chromosome 1 aberrations were detected in 56 samples. There were fewer p1-79 than pUC 1.77 signals in 53 samples. The 1p36 region was deleted in 11 samples in which a single p1-79 signal was detected; seven of these samples were diploid. Abnormalities were found in 17/24 diploid and 30/31 aneuploid tumours.Conclusions-Chromosome 1 aberrations, including deletion of the 1p36 region, were observed in diploid breast tumours. Deletion of the 1p36 region may be an early event in tumorigenesis. Given the frequency and importance of chromosome 1 aberrations in the biological behaviour of breast tumours, FISH, used in conjunction with cytofluorimetry, may be helpful for determining prognosis in patients with diploid tumours.

Evaluation of numerical abnormalities of chromosomes 1 and 17 in proliferative epithelial breast lesions using fluorescence in situ hybridization

Our aim was to investigate the putative role of chromosome abnormalities of chromosomes 1 and 17 in the process of breast carcinogenesis. Numerical abnormalities of chromosomes 1 and 17 were investigated using fluorescence in situ hybridisation (FISH) in a series of 16 primary invasive breast carcinomas associated with intraductal proliferative epithelial lesions. Chromosome 1 aneusomy was detected in 55.6% of ductal hyperplasia (DH), 81.8% of ductal carcinomas in situ (DCIS) and 87.5% of invasive ductal carcinomas (IDC). Chromosome 17 aneusomy was not detected in the cases of DH and was present in 90.9% of DCIS and in 87.5% of IDC. Simultaneous aneusomy of chromosome 1 and 17 was found in 81.8% of DCIS and in 75.0% of IDC. Our results showed that the number of chromosome 1 and 17 copies increases from normal epithelium to invasive cancer. The numerical abnormalities of chromosome 1 were already detected in DH, suggesting that a gain in the copy number of chromosome 1 may be involved early in breast carcinogenesis.

Incidence of chromosomes 1 and 17 aneusomy in breast cancer and adjacent tissue: an interphase cytogenetic study

BACKGROUND

Characterization of the biopathologic events underlying the early steps of breast carcinogenesis may have a dramatic impact on reducing breast cancer mortality. Genes involved in breast tumorigenesis are localized on chromosomes 1 and 17, and numeric aberrations of these chromosomes have been correlated with breast cancer tumorigenesis and progression. According to the field cancerization hypothesis, specific chromosome aberrations may be present in breast cancer and in normal-appearing adjacent tissue. The latter changes reflect the genomic damage that follows longterm carcinogenic exposure and precede the morphologically detectable neoplastic transformation. We hypothesize that detection of these aberrations in benign breast epithelium may provide a tool for molecular risk assessment.

STUDY DESIGN

Using fluorescence in situ hybridization with centromere-specific probes, we determined the status of chromosomes 1 and 17 in fresh imprints of 28 samples of primary tumors and 54 samples of their surrounding uninvolved parenchyma taken from patients undergoing operations for breast carcinoma. Ten contralateral breast biopsy specimens collected from patients with previous breast carcinoma were also evaluated as a surrogate of a high-risk group to rule out the hypothesis that chromosomal aneusomy in tumor-adjacent tissue could be related to a paracrine effect of the primary tumor. Ten samples of benign breast tissue taken from patients at low risk were used as controls to define tolerance limits for aneusomy definition.

RESULTS

Using threshold values of 40% of signal loss and 13% of signal gain to define chromosome aneusomy (ie, mean + 3 SDs of the control group signals), we found the following: 1) almost all primary breast tumors were aneusomic for chromosomes 1 and 17; 2) primary breast tumor and adjacent uninvolved parenchyma shared the same pattern of chromosomes 1 and 17 aneusomy in 66.7% of patients; and 3) chromosomes 1 and 17 aneusomies in contralateral benign breast samples from high-risk patients were not different from those in primary breast tumor or adjacent tissue samples.

CONCLUSIONS

These results suggest that chromosomes 1 and 17 aneusomy may represent an intermediate biomarker of breast tumorigenesis potentially useful to detect patients at high risk of breast carcinoma who may benefit from preventive interventions.

Increasing chromosome 1 copy number parallels histological progression in breast carcinogenesis

Chromosome 1 copy number in the benign breast lesions hyperplasia and atypical duct hyperplasia (ADH) was investigated using fluorescence in situ hybridization on paraffin sections. Progression of chromosome 1 changes occurring in parallel with histological progression from normal through hyperplasia and ADH to ductal carcinoma in situ (DCIS) and invasive carcinoma was also assessed, both overall and within individual patients. The mean signal number for normal cells was 1.14, while that for hyperplasia was 1.56 and ADH was 1.5, while values for DCIS of 1.95 and invasive duct carcinoma of 1.79, were higher (P < 0.001). Six of the seven cases also showed a significant trend towards an increasing proportion of cells with greater than 2 signals per nucleus occurring with histological progression (P < 0.001). These results support the concept that benign proliferative breast disease is a biological precursor of in-situ and invasive ductal carcinoma, the early histological changes possibly indicating a field effect with further genetic changes required for the development of a malignant phenotype.

p53-independent apoptosis and p53-dependent block of DNA rereplication following mitotic spindle inhibition in human cells

We have studied the response of human transformed cells to mitotic spindle inhibition. Two paired cell lines, K562 and its parvovirus-resistant KS derivative clone, respectively nonexpressing and expressing p53, were continuously exposed to nocodazole. Apoptotic cells were observed in both lines, indicating that mitotic spindle impairment induced p53-independent apoptosis. After a transient mitotic delay, both cell lines exited mitosis, as revealed by flow-cytometric determination of MPM2 antigen and cyclin B1 expression, coupled to cytogenetic analysis of sister centromere separation. Both cell lines exited mitosis without chromatid segregation. K562 p53-deficient cells further resumed DNA synthesis, giving rise to cells with a DNA content above 4C, and reentered a polyploid cycle. In contrast, KS cells underwent a subsequent G1 arrest in the tetraploid state. Thus, G1 arrest in tetraploid cells requires p53 function in the rereplication checkpoint which prevents the G1/S transition following aberrant mitosis; in contrast, p53 expression is dispensable for triggering the apoptotic response in the absence of mitotic spindle.

Interphase cytogenetics of chromosomes 11 and 17 in fine needle aspirates of breast cancer

The aims of this investigation were to compare quantitative with qualitative analysis of fluorescent in situ hybridization (FISH) centromere signals in interphase breast cancer cell nuclei and to evaluate the possible clinical utility of detecting numerical abnormalities of chromosomes 11 and 17 by FISH in the preoperative prediction of breast cancer histological grade. Commercial digoxigenin-labeled centromere probes to chromosomes 11 and 17 were hybridized to 69 malignant aspirates with histological follow-up. Aspirates were categorized as disomic or aneusomic for chromosomes 11 and 17 qualitatively; a subset of aspirates was also analyzed quantitatively. The quantitative and qualitative approaches resulted in almost identical categorisation. There was a significant association between the qualitative categorization of aspirates as aneusomic or disomic, the histological grade of the excised tumours (P = .0695, n = 69), and the cytological grade of the clinical aspirates (P = .006, n = 35). Although histological grade III tumors were almost invariably polysomic for one or both chromosomes, polysomy was also detected in grade I and II tumors. Qualitative FISH analysis was shown to be more sensitive than cytological grading in predicting histological grade III but was of lower specificity and was therefore not clinically useful.

Cytogenetics of benign breast lesions

This review summarizes the cytogenetic information on benign breast lesions of various histologies, i.e., fibrocystic lesions from women with and without a known hereditary predisposition to breast cancer, fibroadenomas, phyllodes tumors, and papillomas, and relate the chromosomal features with those in breast carcinoma. In general, the frequency of chromosome abnormalities is lower in benign lesions than in breast cancer, and seems to correlate with the histologic features of the tissue, and the corresponding risk of developing invasive mammary carcinoma; aberrations are more common in proliferative than in nonproliferative lesions. The karyotypes are generally less complex than those detected in invasive carcinoma, and more often involve balanced rearrangements. No lesion-specific aberration has so far been detected; on the contrary, changes repeatedly encountered in breast cancer samples can be found in benign lesions as well, e.g., gain of 1q, interstitial deletion of 3p, and trisomies 7, 18, and 20. Especially intriguing is the prevalence of rearrangements of the short arm of chromosome 3, with the minimally deleted bands 3p13-14, in proliferative lesions from prophylactic mastectomies in breast cancer families. The potential tumor suppressor gene(s) in this region remains, however, to be identified.

Numerical aberrations of chromosomes 1 and 17 in tumor cell lines of the exocrine pancreas as determined by fluorescence in situ hybridization

The relationship between the copy numbers of chromosomes 1 and 17 and characteristics related to aggressiveness, histological grade, and doubling time was studied in 10 cell lines from pancreatic carcinomas (7 from primary tumors, 2 from ascites, and 1 from a liver metastasis). Fluorescence in situ hybridization with, respectively, the (peri-)centromeric pUC 1.77 (chromosome 1), and D17Z1 (chromosome 17) probes was applied to interphase nuclei. The results showed that most of these cell lines were hyperploid for both chromosomes studied in accordance with their chromosome counts in metaphase; moreover, there existed a statistically significant positive correlation between the results for both probes. Two of these cell lines had a higher mean copy number for chromosome 17 than for chromosome 1 (PaCa 44 and PaTu 2); two of them had a higher mean copy number for chromosome 1 than for chromosome 17 (Panc 1 and PSN 1). Although only a weak correlation was observed between the number of signals for either chromosomes 1 or 17 and the doubling time, lines of grade 1 and 2 showed a lower average number of spots per nucleus than grade 3 cell lines for both chromosomes studied.