Mutations in human breast cancer cells: dominantly-acting oncogenes and tumor suppressor genes suggest strategies for targeted interference

Genetic analysis of breast cancer progression

At the histological level, breast tumors display a variety of morphologic lesions which suggest the existence of an increasingly aberrant pathway of intermediate steps leading to the invasive primary tumor and its metastatic dissemination. In order to obtain direct evidence for this presumed progression, underlying genetic changes must be identified. Analyses of primary breast tumors have revealed a large number of dominant and recessive gene alterations encompassing several cellular attributes and activities. It is quite likely that some of these alterations are of a causal nature and thus enable the tumor to attain distinctive malignant phenotypes, such as, dysregulated proliferation, invasion, angiogenesis, and ability to metastasize. Considerable heterogeneity has been observed in the sequence of acquisition of these genetic changes, which is substantiated by recent comparative analyses between carefully microdissected preinvasive and invasive tumor. The data are evaluated here in the context of existing models of breast cancer progression. Implication and prospects for translational application to the clinic are also discussed.

Tumor suppressor p53 mutations and breast cancer: a critical analysis

Alterations in the tumor suppressor gene p53 are the most commonly identified changes in cancer, including neoplasia of the breast. The activity of p53 is regulated post-translationally. Phosphorylation state, subcellular localization, and interaction with any of a number of cellular proteins are likely to influence the function of p53. The exact effect of p53-mediated growth suppression seems to be cell-type specific but appears to be directly related to the ability of p53 to act as a specific transcriptional activator. The role that transcriptional repression plays in the function of WT p53 is less clear. It is also possible that p53 has a more direct activity in DNA replication and repair. Most documented p53 mutations result in single amino acid substitutions which may confer one or more of a spectrum of transforming abilities on the protein. Mutation may lead to nuclear accumulation of p53 protein; however, inactivation of p53 by nuclear exclusion and interaction with the mdm2 protein also appear to be important in tumorigenesis. Used in conjunction with other established factors, accumulation of cellular p53 may be a useful prognostic indicator in breast cancer. A syngeneic mouse model system yielded evidence that p53 mutations are important in the early, preneoplastic stages of mammary tumorigenesis. This murine system may provide the ability to investigate the functions of p53 in the early stages of breast cancer which are technically difficult to examine in the human system.

Molecular biology of breast carcinoma

During the last several years basic research has resulted in the identification of many of the factors involved in signal transduction pathways, leading us to a greater understanding of the mechanisms of growth control in breast cancer cells. Many of these factors are the products of proto-oncogenes or suppressor genes. This review describes the role of some of these factors in breast cancer development, progression, and metastasis and discusses implications for future directions.

Loss of heterozygosity at chromosome 17p is associated with HER-2 amplification and lack of nodal involvement in breast cancer

Sixty DNA samples from breast carcinoma (BC) patients were analyzed by Southern blot to examine certain oncogene and anti-oncogene alterations. Amplification of the HER-2 oncogene was detected in 15 tumours (25%), c-myc in 2 (3%) only and HER-1 in none. Distribution of Hras-1 oncogene alleles in BC did not significantly differ from that seen in healthy donors. Not a single case of RB-1 anti-oncogene alteration and only one of p53 suppressor gene abnormality was found when appropriate cDNA copies were used as probes. With the use of DNA polymorphic markers, loss of heterozygosity (LOH) was revealed at chromosome 17p (probe YNZ-22) in 18 of 39 (46%) informative cases, at 17q (probe THH-59) in 10 of 34 (29%) and at 11p (probe Hras-1) in 8 of 30 (27%). The only significant correlation between these genetic alterations and the clinical characteristics of the tumours studied was the association of LOH at 17p with node-negative BC (p < 0.02). Also, the tendency for correlation (p < 0.2) between HER-2 amplification and loss of 17p sequences was revealed: 7 of 10 amplification-positive, but only 11 of 29 amplification-negative BC possessed LOH of YNZ-22 locus.

Prognostic factors in human primary breast cancer: comparison of c-myc and HER2/neu amplification

Amplification of oncogenes in primary tumours may have prognostic and/or therapeutic significance for patients with breast cancer. We have studied HER2/neu and c-myc amplification together with steroid receptors in human primary breast tumours and related the outcome with (relapse-free) survival. A strong inverse correlation was found between HER2/neu amplification and the presence of oestrogen and progesterone receptors. Actuarial 5-years survival showed that breast cancer patients with c-myc amplification in their primary tumours experience a shorter relapse-free survival, especially in node-negative and in receptor-positive tumours, whereas HER2/neu amplification may be of prognostic value for overall survival in receptor-negative tumours. Overall, in our hands, c-myc amplification appeared to be a more potent prognosticator than HER2/neu amplification in human primary breast cancer.

Prevalence of amplification of the oncogenes c-myc, HER2/neu, and int-2 in one thousand human breast tumours: Correlation with steroid receptors

The frequency of oncogene amplification described in the literature shows a large fluctuation, which could be attributed to the study of relatively small series of tumours, to selection of subgroups of patients, or, especially in retrospective studies, to selection of tumour material from the tumour-bank. To address this question, we have studied amplification of c-myc, HER2/neu and int-2/bcl-1 genes in a series of 1052 collected human breast tumours. The retrospective and prospective subgroups in this collected series of tumours were of equal size. c-myc was amplified in 17.1%, HER2/neu in 18.7% and int-2/bcl-1 in 14.1%, of all breast cancer specimens studied. In the retrospective subgroup the prevalence of amplification was 18.1% for c-myc; 22.6% for HER2/neu and 11.6% for int-2/bcl-1, whereas in the prospective subgroup an incidence of amplification of 16.1%, 15.1% and 16.3% for c-myc, HER2/neu and int-2/bcl-1, respectively was observed. HER2/neu amplification was negatively correlated with oestrogen receptor (ER) and progesterone receptor (PR) status (P less than 0.0001; for both), c-myc amplification was more prevalent in the PR-negative subpopulation (P less than 0.05) and int-2/bcl-1 amplification was positively correlated with ER status (P less than 0.001).