This retrospective study systematically compared mammographic density with histology in women rec... more This retrospective study systematically compared mammographic density with histology in women receiving or not receiving menopausal hormone therapy (HT). This study was approved by the institutional review board. Twenty-eight postmenopausal women using HT were matched with 28 postmenopausal women not using HT at the time of breast cancer diagnosis. Noncancerous tissue from mastectomy specimens was examined histologically to quantitate the content of fibrous stroma, ducts, and lobule types 1, 2, and 3. Tissue samples were also evaluated for estrogen receptor, progesterone receptor, and Ki67 activity in the ducts and lobules. Breast density was quantified by digitizing the contralateral mammogram and computer-assisted interactive thresholding. High breast density in women using HT was correlated with greater fibrous stroma (P = 0.020) and lobule type 1 (P = 0.016). Breast density also correlated with Ki67 activity in the ducts (P = 0.031) and lobules (P= 0.023) for both groups combined. Estrogen and progesterone receptors did not correlate with either breast density or HT use. Increased fibrous stroma and lobule type 1 are associated with increasing mammographic density in women using HT, independent of estrogen and progesterone receptor up-regulation. These findings suggest that increased breast density may be mediated through a paracrine effect. The increase in breast cancer risk with HT use may be due to an increase in target lobule type 1 cells.
The morphological analysis of breast cancer development indicates this to be a multistep process ... more The morphological analysis of breast cancer development indicates this to be a multistep process that progressively evolves from ductal hyperplasia and atypical ductal hyperplasia, which represent the initial stages of neoplastic growth, to carcinoma in situ, invasive carcinoma, and ultimately metastasis, as has been documented for a number of other malignancies. The understanding of the cellular and molecular processes that lead a normal cell to malignancy requires the analysis of pure populations of human breast epithelial cells (HBEC) representing specific stages of neoplastic progression. The neoplastic transformation of HBEC in vitro represents a successful model for obtaining knowledge about the molecular and biological alterations that may contribute to the tumorigenic mechanisms. We present here a current understanding of chemically transformed HBEC in the following aspects: (1) factors affecting the transformation of HBEC such as immortalization; (2) new targets for studying the mechanism of cell immortalization such as alterations in telomerase activity, differential expression of cell cycle-dependent genes, and others recently isolated through differential cloning, such as H-ferritin, and a calcium binding protein; (3) genetic mechanisms underlying cell transformation; and (4) application of the microcell-mediated chromosome transfer technique as an approach to testing the functional role of specific genes whose dysregulation or loss of function may contribute to the ultimate cell transformation. Further efforts in this cell system will be directed to determining the roles of identified molecular changes as well as the mapping/cloning of tumor suppressor or senescence genes.
Epidemiological, clinical, and experimental data indicate that the risk of developing breast canc... more Epidemiological, clinical, and experimental data indicate that the risk of developing breast cancer is strongly dependent on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. Women who gave birth to a child when they were younger than 24 years of age exhibit a decrease in their lifetime risk of developing breast cancer, and additional pregnancies increase the protection. The breast tissue of normally cycling women contains three identifiable types of lobules, the undifferentiated Lobules type 1 (Lob 1) and the more developed Lobules type 2 and Lobules type 3. The breast attains its maximum development during pregnancy and lactation (Lobules type 4). After menopause the breast regresses in both nulliparous and parous women containing only Lob 1. Despite the similarity in the lobular composition of the breast at menopause, the fact that nulliparous women are at higher risk of developing breast cancer than parous women indicates that Lob 1 in these two groups of women might be biologically different, or might exhibit different susceptibility to carcinogenesis. Based on these observations it was postulated that Lob 1 found in the breast of nulliparous women and of parous women with breast cancer never went through the process of differentiation, retaining a high concentration of epithelial cells that are targets for carcinogens and are therefore susceptible to undergo neoplastic transformation. These epithelial cells are called Stem cells 1, whereas Lob 1 structures found in the breast of early parous postmenopausal women free of mammary pathology, on the contrary, are composed of an epithelial cell population that is refractory to transformation, called Stem cells 2. It was further postulated that the degree of differentiation acquired through early pregnancy has changed the 'genomic signature' that differentiates Lob 1 of the early parous women from that of the nulliparous women by shifting the Stem cells 1 to Stem cells 2 that are refractory to carcinogenesis, making this the postulated mechanism of protection conferred by early full-term pregnancy. The identification of a putative breast stem cell (Stem cells 1) has, in the past decade, reached a significant impulse, and several markers also reported for other tissues have been found in the mammary epithelial cells of both rodents and humans. Although further work needs to be carried out in order to better understand the role of the Stem cells 2 and their interaction with the genes that confer them a specific signature, collectively the data presently available provide evidence that pregnancy, through the process of cell differentiation, shifts Stem cells 1 to Stem cells 2 – cells that exhibit a specific genomic signature that could be responsible for the refractoriness of the mammary gland to carcinogenesis.
Hormone Molecular Biology and Clinical Investigation, 2000
Reduction in breast cancer risk is associated with elevated circulating levels of human chorionic... more Reduction in breast cancer risk is associated with elevated circulating levels of human chorionic gonadotropin (hCG) during the first trimester of gestation. The knowledge that hCG also modifies the genomic signature of breast epithelial cells, from highly susceptible to refractory, to undergo neoplastic transformation, and also exerts both preventive and therapeutic effects on chemically induced mammary cancer, lead us to select this hormone for inducing chromatin remodeling in breast epithelial cells as a surrogate end point of complete differentiation and cancer prevention. We have found that chromatin remodeling is the driving force of the differences between the nulliparous and parous breast. In the parous breast, the epithelial cells have a condensed chromatin and increased reactivity with anti-H3K9me2 [di-methyl histone 3 (H3) (Lysine 9)] and H3K27me3 antibodies. This is accompanied by upregulation of noncoding RNA (ncRNA) elements including X2-inactive specific transcript (XIST) and chromatin remodeling genes, such as chromodomain helicase DNA-binding protein 2 (CHD2) and the chromobox homolog 3 (CBX3), whose products are required for controlling recruitment of protein/protein or DNA/protein interactions Another important gene upregulated in the parous breast epithelial cells is the histone-lysine N-methyltransferase or enhancer of zeste homolog 2 (EZH2), a member of the polycomb group (PcG) forming multimeric protein complexes that maintains the transcriptional repressive state of genes over successive cell generations. The fact that recent studies indicate that ncRNAs recruit PcG complexes to the locus of transcription or to sites located elsewhere in the genome cause us to postulate that the increased chromatin condensation in the parous breast has been initiated by ncRNAs, a postulate supported by the observed upregulation of several ncRNAs that included the XIST. The identification of a specific genomic signature of pregnancy has uncovered a novel tool that will serve as a surrogate biomarker for testing new chemopreventive agents and will significantly advance the field of cancer prevention. The clinical impact of this work is that it validates in an experimental system the genomic signature of prevention identified in the human parous breast and establish the bases for the use of the hormone hCG in the prevention of breast cancer, an approach that has not been fully developed until now.
This retrospective study systematically compared mammographic density with histology in women rec... more This retrospective study systematically compared mammographic density with histology in women receiving or not receiving menopausal hormone therapy (HT). This study was approved by the institutional review board. Twenty-eight postmenopausal women using HT were matched with 28 postmenopausal women not using HT at the time of breast cancer diagnosis. Noncancerous tissue from mastectomy specimens was examined histologically to quantitate the content of fibrous stroma, ducts, and lobule types 1, 2, and 3. Tissue samples were also evaluated for estrogen receptor, progesterone receptor, and Ki67 activity in the ducts and lobules. Breast density was quantified by digitizing the contralateral mammogram and computer-assisted interactive thresholding. High breast density in women using HT was correlated with greater fibrous stroma (P = 0.020) and lobule type 1 (P = 0.016). Breast density also correlated with Ki67 activity in the ducts (P = 0.031) and lobules (P= 0.023) for both groups combined. Estrogen and progesterone receptors did not correlate with either breast density or HT use. Increased fibrous stroma and lobule type 1 are associated with increasing mammographic density in women using HT, independent of estrogen and progesterone receptor up-regulation. These findings suggest that increased breast density may be mediated through a paracrine effect. The increase in breast cancer risk with HT use may be due to an increase in target lobule type 1 cells.
The morphological analysis of breast cancer development indicates this to be a multistep process ... more The morphological analysis of breast cancer development indicates this to be a multistep process that progressively evolves from ductal hyperplasia and atypical ductal hyperplasia, which represent the initial stages of neoplastic growth, to carcinoma in situ, invasive carcinoma, and ultimately metastasis, as has been documented for a number of other malignancies. The understanding of the cellular and molecular processes that lead a normal cell to malignancy requires the analysis of pure populations of human breast epithelial cells (HBEC) representing specific stages of neoplastic progression. The neoplastic transformation of HBEC in vitro represents a successful model for obtaining knowledge about the molecular and biological alterations that may contribute to the tumorigenic mechanisms. We present here a current understanding of chemically transformed HBEC in the following aspects: (1) factors affecting the transformation of HBEC such as immortalization; (2) new targets for studying the mechanism of cell immortalization such as alterations in telomerase activity, differential expression of cell cycle-dependent genes, and others recently isolated through differential cloning, such as H-ferritin, and a calcium binding protein; (3) genetic mechanisms underlying cell transformation; and (4) application of the microcell-mediated chromosome transfer technique as an approach to testing the functional role of specific genes whose dysregulation or loss of function may contribute to the ultimate cell transformation. Further efforts in this cell system will be directed to determining the roles of identified molecular changes as well as the mapping/cloning of tumor suppressor or senescence genes.
Epidemiological, clinical, and experimental data indicate that the risk of developing breast canc... more Epidemiological, clinical, and experimental data indicate that the risk of developing breast cancer is strongly dependent on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. Women who gave birth to a child when they were younger than 24 years of age exhibit a decrease in their lifetime risk of developing breast cancer, and additional pregnancies increase the protection. The breast tissue of normally cycling women contains three identifiable types of lobules, the undifferentiated Lobules type 1 (Lob 1) and the more developed Lobules type 2 and Lobules type 3. The breast attains its maximum development during pregnancy and lactation (Lobules type 4). After menopause the breast regresses in both nulliparous and parous women containing only Lob 1. Despite the similarity in the lobular composition of the breast at menopause, the fact that nulliparous women are at higher risk of developing breast cancer than parous women indicates that Lob 1 in these two groups of women might be biologically different, or might exhibit different susceptibility to carcinogenesis. Based on these observations it was postulated that Lob 1 found in the breast of nulliparous women and of parous women with breast cancer never went through the process of differentiation, retaining a high concentration of epithelial cells that are targets for carcinogens and are therefore susceptible to undergo neoplastic transformation. These epithelial cells are called Stem cells 1, whereas Lob 1 structures found in the breast of early parous postmenopausal women free of mammary pathology, on the contrary, are composed of an epithelial cell population that is refractory to transformation, called Stem cells 2. It was further postulated that the degree of differentiation acquired through early pregnancy has changed the 'genomic signature' that differentiates Lob 1 of the early parous women from that of the nulliparous women by shifting the Stem cells 1 to Stem cells 2 that are refractory to carcinogenesis, making this the postulated mechanism of protection conferred by early full-term pregnancy. The identification of a putative breast stem cell (Stem cells 1) has, in the past decade, reached a significant impulse, and several markers also reported for other tissues have been found in the mammary epithelial cells of both rodents and humans. Although further work needs to be carried out in order to better understand the role of the Stem cells 2 and their interaction with the genes that confer them a specific signature, collectively the data presently available provide evidence that pregnancy, through the process of cell differentiation, shifts Stem cells 1 to Stem cells 2 – cells that exhibit a specific genomic signature that could be responsible for the refractoriness of the mammary gland to carcinogenesis.
Hormone Molecular Biology and Clinical Investigation, 2000
Reduction in breast cancer risk is associated with elevated circulating levels of human chorionic... more Reduction in breast cancer risk is associated with elevated circulating levels of human chorionic gonadotropin (hCG) during the first trimester of gestation. The knowledge that hCG also modifies the genomic signature of breast epithelial cells, from highly susceptible to refractory, to undergo neoplastic transformation, and also exerts both preventive and therapeutic effects on chemically induced mammary cancer, lead us to select this hormone for inducing chromatin remodeling in breast epithelial cells as a surrogate end point of complete differentiation and cancer prevention. We have found that chromatin remodeling is the driving force of the differences between the nulliparous and parous breast. In the parous breast, the epithelial cells have a condensed chromatin and increased reactivity with anti-H3K9me2 [di-methyl histone 3 (H3) (Lysine 9)] and H3K27me3 antibodies. This is accompanied by upregulation of noncoding RNA (ncRNA) elements including X2-inactive specific transcript (XIST) and chromatin remodeling genes, such as chromodomain helicase DNA-binding protein 2 (CHD2) and the chromobox homolog 3 (CBX3), whose products are required for controlling recruitment of protein/protein or DNA/protein interactions Another important gene upregulated in the parous breast epithelial cells is the histone-lysine N-methyltransferase or enhancer of zeste homolog 2 (EZH2), a member of the polycomb group (PcG) forming multimeric protein complexes that maintains the transcriptional repressive state of genes over successive cell generations. The fact that recent studies indicate that ncRNAs recruit PcG complexes to the locus of transcription or to sites located elsewhere in the genome cause us to postulate that the increased chromatin condensation in the parous breast has been initiated by ncRNAs, a postulate supported by the observed upregulation of several ncRNAs that included the XIST. The identification of a specific genomic signature of pregnancy has uncovered a novel tool that will serve as a surrogate biomarker for testing new chemopreventive agents and will significantly advance the field of cancer prevention. The clinical impact of this work is that it validates in an experimental system the genomic signature of prevention identified in the human parous breast and establish the bases for the use of the hormone hCG in the prevention of breast cancer, an approach that has not been fully developed until now.
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