Genetic analysis of breast cancer progression

Alcohol and breast cancer: reconciling epidemiological and molecular data

Breast cancer is the most diagnosed cancer in women worldwide. Epidemiological studies have suggested a possible causative role of alcohol consumption as a risk factor for breast cancer. However, such conclusions should be interpreted with considerable caution for several reasons. While epidemiological studies can help identify the roots of health problems and disease incidence in a community, they are by necessity associative and cannot determine cause and effect relationships. In addition, all these studies rely on self-reporting to determine the amount and type of alcoholic beverage consumed, which introduces recall bias. This is documented in a recent study which stated that the apparent increased risk of cancer among light-moderate drinkers may be "substantially due to underreporting of intake." Another meta-analysis about alcohol and breast cancer declared "the modest size of the association and variation in results across studies leave the causal role of alcohol in question." Furthermore, breast cancer develops over decades; thus, correlations between alcohol consumption and breast cancer cannot be determined in epidemiological studies with windows of alcohol exposure that captures current or recent alcohol intake, after clinical diagnosis. Numerous risk factors are involved in breast carcinogenesis; some are genetic and beyond the control of a woman; others are influenced by lifestyle factors. Breast cancer is a heterogeneous and polygenic disease which is further influenced by epigenetic mechanisms that affect the transciptomes, proteomes and metabolomes, and ultimately breast cancer evolution. Environmental factors add another layer of complexity by their interactions with the susceptibility genes for breast cancer and metabolic diseases. The current state-of-knowledge about alcohol and breast cancer association is ambiguous and confusing to both a woman and her physician. Confronting the huge global breast cancer issue should be addressed by sound science. It is advised that women with or without a high risk for breast cancer should avoid overconsumption of alcohol and should consult with their physician about risk factors involved in breast cancer. Since studies associating moderate alcohol consumption and breast cancer are contradictory, a woman and her physician should weigh the risks and benefits of moderate alcohol consumption.

Genomic patterns of allelic imbalance in disease free tissue adjacent to primary breast carcinomas

Mammary stroma plays an important role in facilitating the neoplastic transformation of epithelial cells, modulating integrity of the extracellular matrix, and maintaining genomic stability, but molecular mechanisms by which stroma affects epithelial structure and function are not well-defined. We used laser-assisted microdissection of paraffin-embedded breast tissues from 30 patients with breast disease and a panel of 52 microsatellite markers defining 26 chromosomal regions to characterize genomic patterns of allelic imbalance (AI) in disease-free tissue adjacent to sites of breast disease and to define genomic regions that may contain genes associated with early carcinogenic processes. The mean frequency of AI in histologically normal tissue adjacent to the primary carcinomas (15.4%) was significantly higher than that in distant tissue from the same breast (3.7%). The pattern of AI across all chromosomal regions differed between the adjacent tissue and primary tumor in every case. Unique AI events, observed only in tumor (15% of informative markers) or only in adjacent cells (10% of informative markers), were far more common than AI events shared between tumor and adjacent cells (approximately 4%). Levels of AI characteristic of advanced invasive carcinomas were already present in non-invasive ductal carcinomas in situ, and appreciable levels of AI were observed in adjacent non-neoplastic tissue at all pathological stages. Chromosome 11p15.1 showed significantly higher levels of AI in adjacent cells (p < 0.01), suggesting that this region may harbor genes involved in breast cancer development and progression. Our data indicate that genomic instability may be inherently greater in disease-free tissue close to developing tumors, which may have important implications for defining surgical margins and predicting recurrence.

Modeling the effect of tumor size in early breast cancer

SUMMARY BACKGROUND DATA

The purpose of this study was to determine the type of relationship between tumor size and mortality in early breast carcinoma.

METHODS

The data was abstracted from 83,686 cases registered in the Surveillance, Epidemiology, and End Results Program of women diagnosed with primary breast carcinoma between 1988 and 1997 presenting with a T1-T2 lesion and no metastasis in whom axillary node dissection was performed: 58,070 women were node-negative (N0) and 25,616 were node-positive (N+). End point was death from any cause. Tumor size was modeled as a continuous variable by proportional hazards using a generalized additive models procedure.

RESULTS

Functionally, a Gompertzian expression exp(-exp(-(size-15)/10)) provided a good fit to the effect of tumor size (in millimeters) on mortality, irrespective of nodal status. Quantitatively, for tumor size between 3 and 50 mm, the increase of crude cumulative death rate (number of observed deaths divided by the number of patients at risk) increased with size from 10% to 25% for N0 and from 20% to 40% for N+.

CONCLUSIONS

The functional relationship of tumor size with mortality is concordant with current knowledge of tumor growth. However, its qualitative and quantitative independence of nodal status is in contradiction with the prevailing concept of sequential disease progression from primary tumor to regional nodes. This argues against the perception that nodal metastases are caused by the primary tumor.

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.

Radiation-induced tumorigenesis in preneoplastic mouse mammary glands in vivo: significance of p53 status and apoptosis

In mouse mammary tumorigenesis, p53 mutations facilitate tumorigenesis in concert with other oncogenic alterations. Ionizing radiation enhances tumorigenesis in preneoplastic mammary outgrowth lines and induces p53-dependent apoptosis. We asked if normal p53 function modulates radiation-induced tumorigenesis in preneoplastic mammary lesions by affecting the apoptotic pathway of cell deletion. Three different hyperplastic outgrowth lines were compared. Outgrowth line D1 overexpressed wild-type p53 and responded to irradiation with enhanced tumorigenicity but no induction of apoptosis. Outgrowth line TM12 exhibited normal wild-type p53 expression and responded to irradiation with no alteration in tumorigenicity but with a marked increase in apoptosis. Outgrowth line TM2L also exhibited normal wild-type p53 expression and responded to irradiation with a marked enhancement in both tumorigenicity and apoptosis. These results indicate that the two radiation-induced responses, apoptosis and tumorigenesis, are dissociable events in the mammary gland. Furthermore, radiation-induced tumorigenicity was not abrogated by either enhanced wild-type p53 expression or a robust apoptotic response. The radiation dose of 5 Gy most likely induces multiple genetic alterations in surviving cells, including genomic instability, and this may account for the tumorigenicity. Future experiments will examine lower doses of irradiation that still induce a significant apoptotic response but significantly less genomic instability.

Loss of heterozygosity in normal tissue adjacent to breast carcinomas

Loss of heterozygosity (LOH) was detected in morphologically normal lobules adjacent to breast cancers. The most frequent aberration was at chromosome 3p22-25; of ten cases with this LOH in the carcinoma, six displayed the same LOH in adjacent normal lobules. This suggests that in a subset of sporadic breast cancers, a tumor suppresser gene at 3p22-25 may be important in initiation or early progression of tumorigenesis. Among sixteen breast cancers with LOH at 17p13.1 and five breast cancers with LOH at 11p15.5, one case each displayed the same LOH in adjacent normal lobules. Thus the molecular heterogeneity that characterizes invasive breast cancers may occur at the earliest detectable stages of progression.