Breast cancer cytogenetics and beyond

Cytogenetic evaluation of 20 primary breast carcinomas

Chromosome analysis was performed on samples from 20 Brazilian patients with breast cancer. All the samples were from untreated patients who presented the clinical symptoms for months or years before surgical intervention. Six cases showed axillary lymph node metastases. Clonal chromosome abnormalities were detected in all cases. The numerical alterations most frequently observed involved the loss of chromosomes X, 19, 20, and 22 followed by gain of chromosomes 9 and 8. Among the structural anomalies observed, there was preferential involvement of chromosomes 11, 6, 1, 7, 3, and 12, supporting previous reports that these chromosomes may harbour genes of importance in the development of breast tumors. Two cases with a family history of breast cancer had in common total or partial trisomy 1.

Instability of chromosomes 1, 3, 16, and 17 in primary breast carcinomas inferred by fluorescence in situ hybridization

Abnormalities of chromosomes 1, 3, 16, and 17 were examined in 203 metaphase cells from 12 cases of primary breast carcinoma using fluorescence in situ hybridization with chromosome painting probes. The most common structural abnormalities were chromosomal rearrangements, especially translocations, and chromosome 17 was most frequently involved in these types of changes. Chromosome 16 was preferentially involved in the losses and deletions, while chromosomes 1 and 17 were more involved in the gains, including amplifications, than other chromosomes. This approach has revealed a different profile of abnormalities from those normally shown by G-banding analysis. Some of these changes are likely to be novel and may be biologic or clinical importance in breast cancer.

Microsatellites and PCR genomic analysis

Microsatellites form a significant proportion of the growing family of repetitive DNA sequences, widely dispersed in the human genome. Due to their ubiquity, PCR (polymerase chain reaction) typability, Mendelian co-dominant inheritance, and extreme polymorphism, microsatellites have assumed an increasingly important role as markers in the genome. Apart from their obvious applications in genome mapping and positional cloning, these markers have been applied in fields as disparate as tumour biology, personal identification, population genetic analysis, and the construction of human evolutionary trees. Microsatellites are associated with human disease, not only as markers of risk but also directly in disease aetiopathogenesis, providing new insights into non-Mendelian inheritance; the replication, repair, and mutation of eukaryotic DNA; the regulation of gene transcription; and protein-protein interactions. These insights have resulted in novel paradigms for oncogenesis and neurological disease.

Cytogenetic studies of breast carcinomas: different karyotypic profiles detected by direct harvesting and short-term culture

Chromosome analysis was performed on samples from 85 consecutive patients with breast cancer by one or more of three different methods: direct harvest, culture after mechanical disaggregation, and culture after collagenase digestion. Metaphases suitable for karyotyping were obtained in 70% of the cases; direct harvest yielded metaphases in 29% and cultures without and with digestion in 40% and 59%, respectively. Chromosomal abnormalities were detected in 37 cases. Cells judged to be phenotypically abnormal in culture were twice as likely to reveal chromosomal aberrations as normal-looking cells. Eight cases showed multiclonal abnormalities. Significant differences were detected in the karyotypic profile depending on the method used. With direct harvest, the yield of complex chromosomal changes was 87%, compared to 44% after culture of digested tissue (P < 0.01), and also polyploidy was more common in direct-harvested samples. Detailed karyotypic analysis was possible in 29 primary tumors. The chromosomes most frequently involved were 1, 3, 7, 11, 16, and 17. Recurrent structural abnormalities were der(1;16)(q10;p10), i(1)(q10), del(6)(q21), and del(1)(p22). Breakpoints clustered to the centromere regions of chromosomes 1, 3, 11, 15, and 16 and to the short arms of chromosomes 7, 17, and 19. Seven of twenty-nine fully analyzed cases had a family history of breast cancer, and changes of chromosomes 1, 3, and 15 seemed to be more common in these cases. There was an association between karyotype and survival: The 3 year survival was 63% in patients with complex karyotypic changes and 92% in those without complex changes.

Chromosome 1 aneusomy, identified by interphase cytogenetics, in mammographically detected ductal carcinoma in situ of the breast

Because of the relative rarity of ductal carcinoma in situ (DCIS) in the premammographic screening era, the unavailability of adequate fresh tissue for culture, and the lack of cytogenetic expertise in most pathology departments, there is little information on karyotypic abnormalities in DCIS. The purpose of this study was to investigate the frequency of chromosome 1 aneusomy in DCIS, using interphase cytogenetic techniques, and to correlate the findings with nuclear grade. Twenty-one cases of DCIS, identified in a mammographically screened population, were studied by in situ hybridization. Chromosome 1 numbers were identified in interphase nuclei in conventional histology sections, using a specific centromeric probe (pUC 1.77). In each case, 100 tumour nuclei were compared with 100 normal nuclei. Eighteen of 21 (86 per cent) cases were aneusomic for chromosome 2. This included 15 of 16 (94 per cent) pure comedo or predominantly comedo DCIS. Fifteen of 16 (94 per cent) DCIS with grade 3 nuclei and 3 of 5 (60 per cent) cases with grade 2 nuclei were aneusomic. One case with grade 3 nuclei (a comedo carcinoma) was negative. We conclude that chromosome 1 aneusomy precedes invasion and is a relatively consistent occurrence in those DCIS with high nuclear grade.

Preferential chromosome loss in human papilloma virus DNA-immortalized mammary epithelial cells

Human papilloma virus (HPV) DNA-immortalized human mammary epithelial cells may provide a model system for studying the molecular basis of immortalization and its role in breast neoplasia. Cytogenetic analyses were performed on clones derived from HPV 16- and HPV 18-immortalized human mammary epithelial cells. The majority of the clones contained near-diploid karyotypes. The single most frequent whole-chromosome loss was that of chromosome 19. Regions that showed preference for deletion and/or translocation included 2pter, 11qter, and 15pter. Evidence of chromosome 19 loss was confirmed by polymerase chain reaction (PCR)-generated, chromosome 19-specific, dinucleotide microsatellite repeat polymorphism analysis.

Cytogenetics of epithelial malignant lesions

Chromosomal abnormalities have been believed to be responsible for neoplastic transformation and tumor growth for a long time. The confirming observations are of two types: (1) primary cytogenetic alterations that are responsible for tumor initiation and (2) secondary abnormalities that are acquired late and are associated with tumor growth, heterogeneity, and metastasis. Primary chromosomal abnormalities (such as the 13q deletion in retinoblastoma, 11p deletion in Wilms' tumor, 3p anomalies in renal cell carcinoma, and 5q deletion in colorectal carcinomas) first were identified in lymphocyte cultures as constitutional defects. Later, similar types of defects were observed as tumor-specific aberrations from patients whose lymphocytes otherwise had normal chromosomes. Recently, it has become clear that classes of known cancer-related genes (dominant protooncogenes and recessive tumor-suppressor or anti-oncogenes) are located at those hot spots that are involved in neoplasia-associated chromosomal alterations. In breast carcinoma, such a specific chromosomal alteration has not been identified conclusively in lymphocyte cultures, although chromosome 1 alterations have been observed in cell lines, directly processed effusions, and primary breast tumors. Lymphocyte cultures; primary tumors; and established cell lines from breast carcinomas, colorectal carcinomas, and renal cell carcinomas were analyzed to identify (1) primary chromosomal alterations precisely and (2) secondary cytogenetic defects that are associated with these most common solid adult neoplasms. Peripheral blood analysis indicated that chromosomes 1, 17, and 18 in breast carcinomas; chromosomes 3 and 14 in renal cell carcinomas; and chromosomes 5, 12, and 17 in colorectal carcinomas were involved nonrandomly in structural anomalies in a small number of lymphocyte cells (1-4%). These chromosomal aberrations were considered primary defects because of their involvement as marker formations in tumor cells; other structural and numeric abnormalities also were found. These results indicate that lymphocyte chromosomal analysis might identify those at high risk for breast, colorectal, and renal cell carcinomas, among other malignant lesions. Such identifications could facilitate early selection for primary and secondary cancer prevention or interventional trials.

Rearrangement of chromosome 1p in breast cancer correlates with poor prognostic features

In a cytogenetic study of breast cancer biopsies, clonal abnormalities of chromosome 1p were identified in 56% (14) of 25 informative patients. Translocations predominated, involving 1p22 (n = 1), 1p35 (n = 1) or 1p36 (n = 10) breakpoints. Chromosome 1p abnormalities were associated with estrogen receptor (ER) negativity (P = 0.03, 2-tailed Fisher Exact Probability test), high histological grade (P = 0.02, 2-tailed Mann-Whitney U-test) and an unfavourable Melbourne Prognostic Score (NEPA P = 0.02, SEPA P = 0.04, 2-tailed Mann-Whitney U-tests). These findings are consistent with the possibility that a gene located on chromosome 1p is implicated in tumour progression.

A review of cancer induction by extremely low frequency electromagnetic fields. Is there a plausible mechanism?

A body of epidemiological evidence suggests an association between residential or occupational exposure to extremely low frequency (ELF) electromagnetic fields (EMF) and an increased incidence of cancer in children and adults. Experimental studies at the whole-animal and cellular level are ambiguous; bioeffects suggestive of a carcinogenic effect have been reported, but a similar volume of negative reports can also be assembled. This literature is critically reviewed based on the hypothesis that the epidemiological results are correct, and asking what plausible mechanism could explain a small increase in the incidence of a range of tumors with a non-specific increased exposure to ELF EMF? We focus on four likely mechanisms: 1) disruption of cell communication, 2) modulation of cell growth via changes in calcium ion flux, 3) activation of specific oncogenic gene sequences, and 4) action as a stress factor operating through disruption of hormonal and immune system tumor control mechanisms. We discuss the implications of epidemiologic and experimental results in the context of hypothetical mechanisms of cancer induction, and suggest experiments likely to help define putative EMF hazards.