Chromosome abnormalities in benign hyperproliferative disorders of epithelial and stromal breast tissue

High prevalence of PIK3CA/AKT pathway mutations in papillary neoplasms of the breast

Papillary lesions of the breast have an uncertain relationship to the histogenesis of breast carcinoma, and are thus diagnostically and managerially challenging. Molecular genetic studies have provided evidence that ductal carcinoma in situ and even atypical ductal hyperplasia are precursors of invasive carcinoma. However, papillary lesions have been seldom studied. We screened papillary breast neoplasms for activating point mutations in PIK3CA, AKT1, and RAS protein-family members, which are common in invasive ductal carcinomas. DNA extracts were prepared from sections of 89 papillary lesions, including 61 benign papillomas (28 without significant hyperplasia; 33 with moderate to florid hyperplasia), 11 papillomas with atypical ductal hyperplasia, 7 papillomas with carcinoma in situ, and 10 papillary carcinomas. Extracts were screened for PIK3CA and AKT1 mutations using mass spectrometry; cases that were negative were further screened for mutations in AKT2, BRAF, CDK, EGFR, ERBB2, KRAS, NRAS, and HRAS. Mutations were confirmed by sequencing or HPLC assay. A total of 55 of 89 papillary neoplasms harbored mutations (62%), predominantly in AKT1 (E17K, 27 cases) and PIK3CA (exon 20 >exon 9, 27 cases). Papillomas had more mutations in AKT1 (54%) than in PIK3CA (21%), whereas papillomas with hyperplasia had more PIK3CA (42%) than AKT1 (15%) mutations, as did papillomas with atypical ductal hyperplasia (PIK3CA 45%, AKT1 27%, and NRAS 9%). Among seven papillomas with carcinoma in situ, three had AKT1 mutations. The 10 papillary carcinomas showed an overall lower frequency of mutations, including 1 with an AKT1 mutation (in a tumor arising from a papilloma), 1 with an NRAS gene mutation (Q61H), and 2 with PIK3CA mutations (1 overlapping with the NRAS Q61H). These findings indicate that approximately two-thirds of papillomas are driven by mutations in the PI3CA/AKT pathway. Some papillary carcinomas may arise from these lesions, but others may have different molecular origins.

Analysis of human mammary fibroadenoma by Ki-67 index in the follicular and luteal phases of menstrual cycle

OBJECTIVES

Fibroadenoma is the most common benign mammary condition among women aged 35 or younger. Expression of Ki-67 antigen has been used to compare proliferative activity of mammary fibroadenoma epithelium in the follicular and luteal phases of the menstrual cycle.

MATERIALS AND METHODS

Ninety eumenorrheic women were selected for tumour excision; they were assigned to either of the two groups, according to their phase of menstrual cycle. At the end of the study, 75 patients with 87 masses were evaluated by epithelial cell Ki-67 expression, blind (no information given concerning group to which any lesion belonged).

RESULTS

Both groups were found to be homogeneous relative to age, menarche, body mass index, previous gestation, parity, breastfeeding, number of fibroadenomas, family history of breast cancer and tabagism. Median tumour size was 2.0 cm and no relationship between proliferative activity and nodule diameter was observed. No typical pattern was observed in the expression of Ki-67 in distinct nodules of the same patient. Average values for expression of Ki-67 (per 1000 epithelial cells) in follicular and luteal phases were 27.88 and 37.88, respectively (P = 0.116).

CONCLUSION

Our findings revealed that proliferative activities in the mammary fibroadenoma epithelium did not present a statistically significant difference in the follicular and luteal phases. The present study contributes to clarifying that fibroadenoma is a neoplasm and does not undergo any change in the proliferative activity during the menstrual cycle.

Previously unidentified complex cytogenetic changes found in a pediatric case of solid-pseudopapillary neoplasm of the pancreas

Solid pseudopapillary neoplasm of the pancreas (SPNP) is a rare tumor with low malignant potential found in adolescent girls and young women. The pathogenesis of SPNP remains uncertain and its management is controversial. Genetic changes associated with SPNP have seldom been reported. We describe here the cytogenetic investigation of a case of SPNP in a 13-year-old girl whose tumor cells revealed two unrelated clones: one clone characterized by complex karyotypic changes, including breakpoints in two common fragile sites at chromosome 2, band q33, and chromosome 4, band q31, and the second clone defined by partial monosomy for chromosome X. Loss of heterozygosity for HRAS was also identified by array comparative genomic hybridization (a-CGH). These cumulative changes seem insufficient for activation of cell transformation, but could possibly play a role in priming the cell for future mutagenic events.

Do myoepithelial cells hold the key for breast tumor progression?

Mammary myoepithelial cells have been a neglected facet of breast cancer biology, largely ignored since they have been considered to be less important for tumorigenesis than luminal epithelial cells from which most of breast carcinomas are thought to arise. In recent years as our knowledge of stem cell biology and the cellular microenvironment has been increasing, myoepithelial cells are slowly starting to gain more attention. Emerging data raise the hypothesis whether myoepithelial cells play a key role in breast tumor progression by regulating the in situ to invasive carcinoma transition and that myoepithelial cells are part of the mammary stem cell niche. Paracrine interactions between myoepithelial and luminal epithelial cells are known to be important for regulation of cell cycle progression, establishing epithelial cell polarity, and inhibiting cell migration and invasion. Based on these functions, normal mammary myoepithelial cells have been called "natural tumor suppressors." However, during tumor progression myoepithelial cells seem to loose these properties, and eventually this cell population diminishes as tumors become invasive. Better understanding of myoepithelial cell function and their role in tumor progression may lead to their exploitation for cancer therapeutic and preventative measures.

Lack of DNA copy number alterations revealed with comparative genomic hybridization in fibroadenomas of the breast

There are very few studies reporting DNA copy number changes in fibroadenomas of the breast. Using comparative genomic hybridization, we analyzed 20 paraffin-embedded samples of fibroadenomas of the breast from patients with no familial or previous history of breast cancer. No alterations in the DNA copy number were observed in any of the tumors analyzed, regardless of the chromosomal alterations observed using conventional cytogenetic analysis. We discuss our results and compare them to other reports on fibroadenomas.

Cytogenetic changes in nonmalignant breast tissue

Cytogenetic changes are common in breast cancer and have also been described in fibroadenomas and fibrocystic disease, but not in histologically normal breast tissue. Cytogenetic analysis was performed on nonmalignant breast tissue from benign breast lumps (n = 8), reduction mammoplasties (n = 31), and grossly nontumorous tissue from cancerous breasts (n = 84), using standard techniques and G-banding. All samples were reviewed histologically. Clonal chromosomal changes were found in three of eight benign breast tumors (38%). Of the reduction mammoplasties, 17 samples contained nonproliferative changes, and three of these (18%) showed a clonal deletion of 3p. No pathology was identified in the other 14 samples, of which one (7%) contained two clonal changes, apparently balanced translocations. Of nontumorous tissues from cancerous breasts, 15 (18%) showed clonal chromosomal abnormalities. Five of these samples were histologically normal. Two clones were identical to those found in the corresponding cancer. In 18 additional samples, single cells were detected with the same change as that seen in clones or single cells in the cancer. Only 4 of these 20 samples contained detectable cancer cells. Clonal abnormalities found in two or more samples included trisomies X, 7, and 20 and monosomies 19 and 18. Clonal changes were not significantly more frequent in proliferative than in nonproliferative lesions. The Icelandic BRCA2 founder mutation, 999del5, was detected in four samples, all histologically normal, two of which had clonal chromosomal abnormalities. In conclusion, clonal chromosomal changes are not infrequent in nonmalignant breast tissue and can be detected even in the absence of histological abnormalities.

Loss of heterozygosity in normal breast epithelial tissue and benign breast lesions in BRCA1/2 carriers with breast cancer

Loss of heterozygosity (LOH) of the wild-type BRCA1/2 allele is a reproducible event in breast tumors of BRCA1/2 mutation carriers, but it is unknown if this allelic loss occurs only in association with recognizable histopathologic abnormalities. We evaluated the early genomic changes that occur in the mammary glands of patients with increased predisposition to breast cancer due to germline mutations in the BRCA1/2 genes. We tested the hypothesis that these genomic changes may be detected, not only in histologically abnormal and malignant breast tissues, but also in morphologically normal tissues and in areas with pathologically benign changes. Samples were obtained from five breast cancer patients: four BRCA1 carriers and one BRCA2 carrier. In each case, nontumor tissue areas surrounding the tumor or from other locations of the breast were isolated using laser capture microdissection. We evaluated 29 areas showing normal terminal ductal lobular units (TDLUs) or histopathologically benign changes (in particular, sclerosing adenosis), using a panel of polymorphic dinucleotide microsatellite markers for the BRCA1 gene and other chromosome 17 loci, for the BRCA2 gene and other chromosome 13 loci, and for the FHIT gene on 3p14.2. Overall, we analyzed a total of 105 samples of nontumor tissues; LOH was detected in 59 of the 105 (56%). In the normal TDLUs, 15 of 30 samples (50%) showed LOH; in the tissues with benign proliferative changes, such as sclerosing adenosis, 44 of 75 samples showed LOH (59%). Our results suggest that there is a field effect of early genetic events preceding morphologic changes in the mammary glands of BRCA mutation carriers.

Polyclonal Development of Mouse Mammary Preneoplastic Nodules

Studies of cellular interactions are critical to the understanding of tumorigenesis. Although many studies have demonstrated a monoclonal composition of advanced neoplasms in humans and mice, the clonal composition of smaller, antecedent lesions has been studied less thoroughly. To examine the clonal development of breast cancer, we generated chimeric mammary glands using mouse mammary epithelium with an inherited predisposition for neoplasia. Analysis of whey acidic protein-transforming growth factor-alpha transgenic mouse mammary glands, chimeric for two different cell lineage markers, revealed that mammary ducts and alveoli are polyclonal, and putative early preneoplastic lesions, hyperplastic alveolar nodules (HANs), frequently are polyclonal. Furthermore, the chimeric patch patterns in individual HANs were similar to the patterns observed in pregnant chimeric mammary glands. Thus, polyclonality in HANs appears to reflect persistence of the polyclonal architecture of ducts and/or alveoli, suggesting that hyperplasia formation can be the result of non-cell autonomous local tissue microenvironmental influences on groups of cells, rather than clonal progression of a single initiated cell.

Estrogen and its metabolites are carcinogenic agents in human breast epithelial cells

Estrogens play a crucial role in the development and evolution of human breast cancer. However, it is still unclear whether estrogens are carcinogenic to the human breast. There are three mechanisms that have been considered to be responsible for the carcinogenicity of estrogens: receptor-mediated hormonal activity, a cytochrome P450 (CYP)-mediated metabolic activation, which elicits direct genotoxic effects by increasing mutation rates, and the induction of aneuploidy by estrogen. To fully demonstrate that estrogens are carcinogenic in the human breast through one or more of the mechanisms explained above it will require an experimental system in which, estrogens by itself or one of the metabolites would induce transformation phenotypes indicative of neoplasia in HBEC in vitro and also induce genomic alterations similar to those observed in spontaneous malignancies. In order to mimic the intermittent exposure of HBEC to endogenous estrogens, MCF-10F cells that are ERalpha negative and ERbeta positive were first treated with 0, 0.007, 70 nM and 1 microM of 17beta-estradiol (E(2)), diethylstilbestrol (DES), benz(a)pyrene (BP), progesterone (P), 2-OH-E(2), 4-hydoxy estradiol (4-OH-E(2)) and 16-alpha-OH-E(2) at 72 h and 120 h post-plating. Treatment of HBEC with physiological doses of E(2), 2-OH-E(2), 4-OH-E(2) induce anchorage independent growth, colony formation in agar methocel, and reduced ductulogenic capacity in collagen gel, all phenotypes whose expression are indicative of neoplastic transformation, and that are induced by BP under the same culture conditions. The presence of ERbeta is the pathway used by E(2) to induce colony formation in agar methocel and loss of ductulogenic in collagen gel. This is supported by the fact that either tamoxifen or the pure antiestrogen ICI-182,780 (ICI) abrogated these phenotypes. However, the invasion phenotype, an important marker of tumorigenesis is not modified when the cells are treated in presence of tamoxifen or ICI, suggesting that other pathways may be involved. Although we cannot rule out the possibility, that 4-OH-E(2) may interact with other receptors still not identified, with the data presently available the direct effect of 4-OH-E(2) support the concept that metabolic activation of estrogens mediated by various cytochrome P450 complexes, generating through this pathway reactive intermediates that elicit direct genotoxic effects leading to transformation. This assumption was confirmed when we found that all the transformation phenotypes induced by 4-OH-E(2) were not abrogated when this compound was used in presence of the pure antiestrogen ICI. The novelty of these observations lies in the role of ERbeta in transformation and that this pathway can successfully bypassed by the estrogen metabolite 4-OH-E(2). Genomic DNA was analyzed for the detection of micro-satellite DNA polymorphism using 64 markers covering chromosomes (chr) 3, 11, 13 and 17. We have detected loss of heterozygosity (LOH) in ch13q12.2-12.3 (D13S893) and in ch17q21.1 (D17S800) in E(2), 2-OH-E(2), 4-OH-E(2), E(2) + ICI, E(2) + tamoxifen and BP-treated cells. LOH in ch17q21.1-21.2 (D17S806) was also observed in E(2), 4-OH-E(2), E(2)+ICI, E(2)+tamoxifen and BP-treated cells. MCF-10F cells treated with P or P+E(2) did not show LOH in the any of the markers studied. LOH was strongly associated with the invasion phenotype. Altogether our data indicate that E(2) and its metabolites induce in HBEC LOH in loci of chromosomes 13 and 17, that has been reported in primary breast cancer, that the changes are similar to those induced by the chemical carcinogen (BP) and that the genomic changes were not abrogated by antiestrogens.

Application of comparative genomic hybridization in search for genetic aberrations in fibroadenomas of the breast

We applied a comparative genomic hybridization (CGH) technique to paraffin-embedded tissue samples taken from fibroadenomas, benign breast tumors, to detect possible numerical and unbalanced genetic changes. We compared the results to those from previous cytogenetic studies of fibroadenomas. In concurrence with previous cytogenetic studies of fibroadenomas, we detected genetic aberrations in chromosomes 4-6, 8-13, 16, 18, 19, 20, and 22. In addition, with the CGH technique we were able to find two new aberrations, 15q+ and 16p-. Because these aberrations have also been reported to be present in breast cancer, the importance of this finding is yet to be determined.

Analysis of the progression of fibroepithelial tumours of the breast by PCR-based clonality assay

Fibroadenoma and phyllodes tumour of the breast are both fibroepithelial tumours. Although progression to epithelial malignancy has been described, the behaviour of most fibroadenomas is benign. Phyllodes tumours, on the other hand, can display locally destructive growth and can even metastasize. A relationship between the two tumours has been suggested in the literature. This study investigated the clonality of both the stroma and the epithelium of these fibroepithelial tumours and attempted to construct a model in which fibroadenoma can progress in both an epithelial and a stromal direction. Fibroadenomas (n=25) and phyllodes tumours (n=12) were selected for analysis. Tissue was microdissected and analysed for clonality using a polymerase chain reaction (PCR)-based assay targeted at an X-linked polymorphic marker, the human androgen receptor gene (HUMARA). Nineteen fibroadenomas and nine phyllodes tumours could be analysed. Normal-appearing epithelium, hyperplastic epithelium, and stroma removed from fibroadenomas were polyclonal. As expected, carcinoma in situ (CIS) removed from four fibroadenomas was monoclonal. Three areas of apparent stromal expansion within fibroadenoma were monoclonal, suggesting stromal progression. Mostly, the stroma of phyllodes tumours was monoclonal and the epithelium polyclonal. In two cases, however, the epithelium seemed to be monoclonal, whereas in three other cases the stromal component was polyclonal. These findings indicate that fibroadenoma can progress in an epithelial direction to CIS and in a stromal direction to phyllodes tumour.

Comparative genomic hybridization analysis of benign and invasive male breast neoplasms

Comparative genomic hybridization (CGH) analysis was performed for the identification of chromosomal imbalances in two benign gynecomastias and one malignant breast carcinoma derived from patients with male breast disease and compared with cytogenetic analysis in two of the three cases. CGH analysis demonstrated overrepresentation of 8q in all three cases. One case of gynecomastia presented gain of 1p34.3 through pter, 11p14 through q12, and 17p11.2 through qter, and loss of 1q41 through qter and 4q33 through qter. The other gynecomastia presented del(1)(q41) as detected by both cytogenetic and CGH analysis. CGH analysis of the invasive ductal carcinoma confirmed a gain of 17p11.2 through qter previously detected by cytogenetic analysis. These regions showed some similarity in their pattern of imbalance to the chromosomal alterations described in female and male breast cancer.

Cytogenetic clues to breast carcinogenesis

The somatic mutation theory of cancer maintains that tumorigenesis is driven by genetic alterations, many of which are visible cytogenetically. We have examined breast cancer by chromosome banding analysis after short-term culturing of tumor cells and here review our findings in 322 karyotypically abnormal samples obtained since 1992 from 256 patients. The screening capabilities of this technique enabled us to identify several cytogenetic subgroups of breast cancer, to study the intratumor heterogeneity of breast carcinomas, and to compare primary tumors with their metastases. Using chromosome abnormalities as clonality markers, we could determine on an individual basis when multiple, ipsilateral or bilateral breast, tumors were independent de novo carcinomas and when they resulted from the spreading of a single malignant clone within one breast or from one breast to the other. The distribution of chromosomal breakpoints and genomic gains and losses is clearly nonrandom in breast cancer, something that can guide further investigations using molecular methods. Based on the total dataset, we propose a multipathway model of mammary carcinogenesis that takes into consideration the genetic heterogeneity revealed by the karyotypic findings and review the karyotypic-pathologic correlations and the possible clinical applications of the cytogenetic knowledge.

Clonal chromosomal alterations in fibroadenomas of the breast

A cytogenetic study on short-term cell cultures from 10 fibroadenomas of the breast is reported. Clonal chromosomal alterations were observed in all cases analyzed, involving preferentially chromosomes X, 12, 14, 20, and 22. Normal karyotypes were found in 34.9% of the cells. The present findings are discussed together with the reports on fibroadenomas and other benign lesions of the breast described in the literature. Although no specific chromosome abnormality to date can be attributed to a particular type of benign breast pathology, some recurrent alterations are starting to emerge and may characterize these benign breast lesions, differentiating them from their malignant counterparts.

On the birth of breast cancer

Breast carcinoma is one of the most common neoplasms in women and is a leading cause of cancer related deaths worldwide. In recent years improved diagnostic tools have made it possible to detect breast cancers at early, even pre-invasive stages leading to a significant decrease in breast cancer mortality rates over the past decades. The increased number of patients diagnosed with pre-invasive breast tumors opened up new avenues in research and new dilemmas in clinical practice, since our understanding of the pathophysiology of such lesions is just beginning to emerge. Part of the delay and difficulty with analyzing pre-invasive tumors including ductal carcinoma in situ has been due to the lack of appropriate techniques suitable for studies of small, frequently microscopic size tumors. Recently developed technologies such as DNA microarrays and SAGE (serial analysis of gene expression) have made it possible to obtain comprehensive gene expression profiles of breast carcinomas of all stages. The application of these genomics approaches in combination with the complete sequence of the human genome and extensive molecular epidemiological studies is likely to further our understanding of the molecular basis of mammary tumorigenesis and will identify targets for risk prediction, cancer prevention and treatment.

Profiling of differentially expressed genes induced by high linear energy transfer radiation in breast epithelial cells

Methods to define patterns of gene expression have applications in a wide range of biological systems. Several molecular biological techniques are used to study expression patterns during the neoplastic progression of breast epithelial cells. In the present study, differential expression of human oncogenes/tumor suppressor genes in human breast epithelial cell lines irradiated with low doses of high linear energy transfer radiation and treated with estrogen was assessed with cDNA expression arrays. Transformed and tumorigenic cell lines were compared with the control cell line to identify differentially expressed genes during tumorigenic progression. Autoradiographic analysis showed that of the 190 genes analyzed, 49 genes showed a high level of altered expression, and 12 genes had minor differences in expression levels. Among these 49 genes, 17 genes were altered at all stages of transformation, 21 were altered only at the early stage, and the remaining 11 were at the late stage of transformation to the tumorigenic stage of progression. Among the 11 late stage-associated genes, seven genes were altered exclusively in the tumorigenic cell lines and in Tumor-T. Of the 17 all-stage genes, six were randomly selected, and we confirmed their altered expression by gene-specific semiquantitative reverse transcription polymerase chain reaction, followed by Northern blot analysis. The results showed that the mRNA expression patterns of all these genes were consistent with the expression pattern seen on the array. Among these six genes, five genes, including c-myc, puf, MNDA, c-yes, and Fra-1 showed upregulation, and the other gene, RBA/p48, showed downregulation in the transformed and tumorigenic cell lines compared with the control MCF-10F cell line. Investigation of these genes should help establish the molecular mechanisms of progression that are altered by radiation and estrogen treatment. A number of candidates reported here should be useful as biomarkers involved in breast carcinogenesis.

Clonal origins of human breast cancer

Tumours are usually considered as the clonal progeny of single transformed cells. An X-chromosome inactivation assay has been applied to exploring clonal relationships in human breast cancer. Analysis of X-inactivation in DNA extracted from microdissected in situ and invasive breast carcinoma by Hpa II restriction and polymerase chain reaction (PCR) of the androgen receptor exon I CAG polymorphism confirmed monoclonality in 105/133 samples of carcinoma cells from 31/32 informative breast cancers. Clonality was identical in seven cases between in situ and invasive carcinoma. Unexpectedly, 4 of 12 cancers (33%) with two or more monoclonal samples available were mosaic (polyclonal) in respect of X-chromosome inactivation between separate morphologically homogeneous tumour cell samples. Concordant clonality supports a common clonal origin of in situ and invasive breast cancers, but frequent apparently mosaic X-inactivation in breast cancer cannot be explained by non-tumour cell contamination. It is concluded that these carcinomas may be genuinely multiclonal. Possible mechanisms of multiclonality include simultaneous transformation of cell groups straddling X-chromosome inactivation patch boundaries, tumour-initiating mutations prior to X-inactivation, or recruitment of bystander stem cells by DNA transfer from necrotic or apoptotic tumour cells. Collision of independent cancers appears implausible at this frequency. Further studies using independent analytical techniques are required to test the important possibility that a significant proportion of mammary carcinomas are not monoclonal.

High-resolution chromosome 3p allelotyping of breast carcinomas and precursor lesions demonstrates frequent loss of heterozygosity and a discontinuous pattern of allele loss

We performed high-resolution allelotyping for loss of heterozygosity (LOH) analysis on microdissected samples from 45 primary breast cancers, 47 mammary preneoplastic epithelial foci, and 18 breast cancer cell lines, using a panel of 27 polymorphic chromosome 3p markers. Allele loss in some regions of chromosome 3p was detected in 39 of 45 (87%) primary breast tumors. The 3p21.3 region had the highest frequency of LOH (69%), followed by 3p22-24 (61%), 3p21.2-21.3 (58%), 3p25 (48%), 3p14.2 (45%), 3p14.3 (41%), and 3p12 (35%). Analysis of all of the data revealed at least nine discrete intervals showing frequent allele loss: D3S1511-D3S1284 (U2020/DUTT1 region centered on D3S1274 with a homozygous deletion), D3S1300-D3S1234 [fragile histidine triad (FHIT)/FRA3B region centered on D3S1300 with a homozygous deletion], D3S1076-D3S1573, D3S4624/Luca2.1-D3S4597/P1.5, D3S1478-D3S1029, D3S1029 (with a homozygous deletion), D3S1612-D3S1537, D3S1293-D3S1597, and D3S1597-telomere; it is more than likely that additional localized regions of LOH not examined in this study also exist on chromosome 3p. In multiple cases, there was discontinuous allele loss at several 3p sites in the same tumor. Twenty-one of 47 (45%) preneoplastic lesions demonstrated 3p LOH, including 12 of 13 (92%) ductal carcinoma in situ, 2 of 7 (29%) apocrine metaplasia, and 7 of 25 (28%) usual epithelial hyperplasia. The 3p21.3 region had the highest frequency of LOH in preneoplastic breast epithelium (36%), followed by 3p21.2-21.3 (20%), 3p14.2/FHIT region (11%), 3p25 (10%), and 3p22-24 (5%). In 39 3p loci showing LOH in both the tumor and accompanying preneoplasia, 34 (87%) showed loss of the same parental allele (P = 1.2 x 10(-6), cumulative binomial test). In addition, when 21 preneoplastic samples showing LOH were compared to their accompanying cancers, 67% were clonally related, 20% were potentially clonally related but were divergent, and 13% were clonally unrelated. Overall this demonstrated the high likelihood of clonal relatedness of the preneoplastic foci to the tumors. We conclude that: chromosome 3p allele loss is a common event in breast carcinoma pathogenesis; involves multiple, localized sites that often show discontinuous LOH with intervening markers retaining heterozygosity; and is seen in early preneoplastic stages, which demonstrate clonal relatedness to the invasive cancer.

Comparative genomic hybridization detects novel amplifications in fibroadenomas of the breast

Comparative genomic hybridization analysis was performed for identification of chromosomal imbalances in 23 samples of fibroadenomas of the breast. Chromosomal gains rather than losses were a feature of these lesions. Only two cases with a familial and/or previous history of breast lesions had gain of 1q or 16q as the sole abnormality. The most frequently overrepresented segments were 5p14 (10/23 cases), 5q34-qter (6/23 cases), 13q32-qter (6/23 cases), 10q25-qter (5/23 cases), and 18q22 (4/23 cases). Some of these regions have previously been associated with breast carcinoma, but this study indicates that gain of these regions can also occur in benign breast lesions. Our findings may provide a basis for conducting further investigations to locate and identify genes associated with proliferation that may be involved in the early steps of tumorigenesis of the breast.

Carcinogenicity of estrogens in human breast epithelial cells

Epidemiological and clinical evidences indicate that breast cancer risk is associated with prolonged ovarian function that results in elevated circulating levels of steroid hormones. Principal among these is estrogen, which is associated with two important risk factors, early onset of menarche and late menopause. However, up to now there is no direct experimental evidence that estrogens are responsible of the initiation of human breast cancer. We postulate that if estrogens are causative agents of this disease, they should elicit in human breast epithelial cells (HBEC) genomic alterations similar to those exhibited by human breast cancers, such as DNA amplification and loss of genetic material representing tumor suppressor genes. These effects could result from binding of the hormone to its nuclear receptors (ER) or from its metabolic activation to reactive metabolites. This hypothesis was tested by treating with the natural estrogen 17beta-estradiol (E2) and the synthetic steroid diethylstilbestrol (DES) MCF-10F cells, a HBEC line that is negative for ER. Cells treated with the chemical carcinogen benzo (a) pyrene (BP) served as a positive control of cell transformation. BP-, E2-, and DES-treated MCF-10F cells showed increases in survival efficiency and colony efficiency in agar methocel, and loss of ductulogenic capacity in collagen gel. The largest colonies were formed by BP-treated cells, becoming progressively smaller in DES- and E2-treated cells. The loss of ductulogenic capacity was maximal in BP-, and less prominent in E2- and DES-treated cells. Genomic analysis revealed that E2- and DES-treated cells exhibited loss of heterozygosity in chromosomes 3 and 11, at 3p21, 3p21-21.2, 3p21.1-14.2, and 3p14.2 14.1, and at 11q23.3 and 11q23.1-25 regions, respectively. It is noteworthy that these loci are also affected in breast lesions, such as ductal hyperplasia, carcinoma in situ, and invasive carcinoma. Our data are the first ones to demonstrate that estrogens induce in HBEC phenotypic changes indicative of cell transformation and that those changes are associated with significant genomic alterations that might unravel new pathways in the initiation of breast cancer.

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.

Cytogenetics of epithelial hyperplasias of the human breast

Generally, benign breast lesions behave like innocuous and limited proliferations; however, sometimes they can represent precancerous pathologies. The cytogenetic analysis of five mammary epithelial hyperplasias is reported. Four cases had clonal chromosome alterations. All of the cases presented a modal number of 46 chromosomes. Chromosome 9 monosomies and chromosome 1 deletions were common in these benign tumors. The study of benign proliferations of the breast may reveal a possible relationship between chromosomal alterations and the conditions of the tissue.

The clonal origin and clonal evolution of epithelial tumours

While the origin of tumours, whether from one cell or many, has been a source of fascination for experimental oncologists for some time, in recent years there has been a veritable explosion of information about the clonal architecture of tumours and their antecedents, stimulated, in the main, by the ready accessibility of new molecular techniques. While most of these new results have apparently confirmed the monoclonal origin of human epithelial (and other) tumours, there are a significant number of studies in which this conclusion just cannot be made. Moreover, analysis of many articles show that the potential impact of such considerations as patch size and clonal evolution on determinations of clonality have largely been ignored, with the result that a number of these studies are confounded. However, the clonal architecture of preneoplastic lesions provide some interesting insights --many lesions which might have been hitherto regarded as hyperplasias are apparently clonal in derivation. If this is indeed true, it calls into some question our hopeful corollary that a monoclonal origin presages a neoplastic habitus. Finally, it is clear, for many reasons, that methods of analysis which involve the disaggregation of tissues, albeit microdissected, are far from ideal and we should be putting more effort into techniques where the clonal architecture of normal tissues, preneoplastic and preinvasive lesions and their derivative tumours can be directly visualized in situ.

Molecular analysis of phyllodes tumors reveals distinct changes in the epithelial and stromal components

Phyllodes tumors are fibroepithelial mammary lesions that tend to behave in a benign fashion but may undergo sarcomatous transformation. A study of clonality in these tumors has suggested that the epithelial component is polyclonal, but the stroma is monoclonal, and thus forms the neoplastic component of the lesion. In this study microsatellites on chromosome 1q and chromosome 3p were assessed for allelic imbalance (AI) in 47 phyllodes tumors; in all cases stroma and epithelium were analyzed separately. Ten of 42 (24%) phyllodes tumors showed AI at one or more markers on 3p, and 14 of 46 (30%) showed AI on chromosome 1. Five tumors had changes in both the epithelium and stroma. Eight tumors had changes only detectable in the stroma and eight, changes in the epithelium only. Three tumors exhibited low-level microsatellite instability in the epithelium but not in the stroma. The results show that AI on 3p and 1q does occur in phyllodes tumors and that it can occur in both the stroma and epithelium, sometimes as independent genetic events. These unexpected findings throw into doubt the classical view that phyllodes tumors are simply stromal neoplasms and raise questions about the nature of stromal and epithelial interactions in these tumors.

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.

Genetic heterogeneity in ductal carcinoma of the breast

Genetic heterogeneity in breast cancer has been observed both by cytogenetic and loss of heterozygosity (LOH) analyses; however, the frequency with which genetically heterogeneous clones arise is unknown. In this study, a panel of 115 breast carcinomas was analyzed to determine the extent of clonal divergence in tumor foci at progressive stages of tumor evolution. Intraductal, infiltrating, and metastatic tumor components were microdissected from each tumor and tested for LOH at 20 microsatellite markers on seven chromosomal arms. Of these cases, 24 (21%) demonstrated genetically divergent clones during tumor progression. Clonal divergence, inferred from discordant LOH patterns, was observed most commonly between intraductal and infiltrating tumor (18 cases), but was also demonstrated between infiltrating and metastatic tumor (11 cases). Discordant LOH was observed with markers on one chromosomal arm in 16 cases, on two in 7 cases, and on four in 1 case, and was observed most commonly with markers on 17p, 17q, and 16q. More detailed microdissection of four cases provided evidence for a specific chronology of genetic alterations occurring during the progression of each tumor. The results indicate that the different tumor components observed microscopically in breast cancer specimens often represent genetically divergent clones.

Use of archival fine-needle aspirates for the allelotyping of tumors

BACKGROUND

Loss of heterozygosity (LOH) analysis (allelotyping) based on polymorphic microsatellite DNA is one of the most powerful molecular tools currently available for studying carcinogenesis. However, allelotyping studies that require archival paraffin embedded tissues are often hampered by technical difficulties related to microdissection and poor DNA quality.

METHODS

The authors compared allelotyping results from 12 paraffin embedded breast carcinoma cases with those from matching alcohol fixed fine-needle aspiration (FNA) cytology slides obtained for routine diagnostic purposes, using 30 polymorphic microsatellite markers at chromosomes 3p, 4p, 4q, 5q, 6p, 8p, 9p, 11q, 17p, and 17q. Cells from the alcohol fixed FNA slides were dissected and processed in three different ways, and DNA dilution experiments were performed to determine the minimum number of cells required for accurate allelotyping.

RESULTS

LOH results were identical for paraffin embedded and alcohol fixed tumors for 97% of 114 polymerase chain reactions (PCR) when 1000-2000 cells were dissected from each FNA slide and DNA from 100 cells was used for each multiplex PCR. However, with lower cell numbers, the discordance rate increased and artifactual LOH was observed. Intratumor allelotype heterogeneity could not be documented.

CONCLUSIONS

The use of alcohol fixed cytology preparations improves the ease of PCR-based allelotyping and greatly expands the range of archival materials available for study. The allelotyping is accurate and reproducible when DNA from >/=25 cells is used in the initial multiplex PCR. Cancer (Cancer Cytopathol)

Clonal karyotypic abnormalities in gynecomastia

Gynecomastia is a benign condition that frequently occurs in the male breast gland; however, the cytogenetic data on this entity are very limited. To our knowledge, three cases have been reported in the literature, and the only one with an abnormal karyotype had a concomitant breast carcinoma. In this study we report clonal chromosomal alterations in a gynecomastia sample without any signs of adjacent malignant tissue. The nonrandom abnormalities observed were a deletion of 12p, monosomies of chromosomes 9, 17, 19, and 20, and the presence of a marker chromosome. Most of these alterations have been previously described in the literature in other breast lesions, including benign and malignant (male and female) tumors, indicating their recurrence and nonrandomness in abnormal processes of the mammary gland.

Multiple polysomies in breast carcinomas: preferential gain of chromosomes 1, 5, 6, 7, 12, 16, 17, 18, and 19

Chromosome G-banding analysis of metaphase cells from 16 primary breast carcinomas revealed the presence of multiple polysomies in near-diploid as well as in polyploid cells. Chromosome 17 was preferentially gained in 7 tumors, followed in frequency by chromosomes 1, 12, and 19 (5 tumors each), and chromosomes 5, 6, 7, 16, and 18 (4 tumors each). Eleven of the 16 carcinomas had, apart from the clones exhibiting the numerical gains, other unrelated clones. Nine of these 11 cases had clones with structural chromosome aberrations, 5 of which had structural aberrations involving the short arm of chromosome 3. The biologic significance, if any, of this seemingly nonrandom coexistence of multiple polysomies with structural aberrations of 3p is at present not known. The pattern of numerical chromosome aberrations observed in the present study is comparable to previous results from fluorescence in situ hybridization (FISH) studies, with the use of centromeric probes on interphase cells. However, unlike FISH studies, which have been focused on chromosomes 1, 3, 7, 8, 11, 16, and 17, the cytogenetic results reveal that other chromosomes also may be nonrandomly gained as part of multiple polysomies in breast carcinomas. In addition, the tumors with multiple polysomies were generally of high histologic grade and with metastasis to axillary lymph nodes, suggesting that multiple wholechromosome gains may be a pathway of genetic evolution or progression or both in some breast carcinomas.

Loss of heterozygosity at 3p in benign lesions preceding invasive breast cancer

BACKGROUND

Loss of heterozygosity (LOH) at chromosome 3p is one of the most common genetic abnormalities identified in human cancers and has occasionally been noted in benign proliferative lesions predisposing to breast cancer. If the frequency of LOH at 3p in benign proliferative lesions correlates with the subsequent development of breast cancer, it may be possible to develop powerful tools for molecular risk assessment based on this technology.

MATERIALS AND METHODS

Archival paraffin-embedded tissues from benign breast biopsies in five women who have developed breast cancer and three women who have not developed breast cancer were microdissected and allelotyped at 3p using six microsatellite markers.

RESULTS

No LOH was detected in the biopsies from women who have not developed breast cancer. For women developing breast cancer, the proportion of informative loci showing LOH in the benign proliferative lesions was 0.47 as compared to 0.57 for the associated breast cancers. There was no LOH detected in epithelial DNA from a fibroadenoma. Of 15 informative loci, 4 (27%) showed LOH in both the benign proliferative lesion and the associated cancer; however, the actual parental allele lost was different in three of these four cases.

CONCLUSIONS

These results suggest that there are specific patterns of genetic instability common to preneoplastic lesions and the breast cancers that subsequently develop even when the paired lesions are not clonally related. LOH analysis of benign breast epithelium may provide a tool for molecular risk assessment and a surrogate endpoint for breast cancer chemoprevention trials.

Field cancerization, clonality, and epithelial stem cells: the spread of mutated clones in epithelial sheets

There has been considerable debate about the origin of human tumours, whether they arise from a single cell and are clonal populations or whether there needs to be some sort of co-operativity between cells for the neoplastic process to begin. Current theories subscribe to the clonal view, where a series of mutations in one cell begins a process of selection and clonal evolution leading to the development of the malignant phenotype. This review approaches this problem by asking how mutated clones, once established, spread through tissues before becoming overtly invasive. While there is substantial evidence in favour of independent origins of each tumour from a unique mutated clone, there are instances where such clones expand and remain cohesive, often involving a large area of tissue. The main example is the movement of mutated clonal crypts through the colorectal epithelium, by the process of crypt fission. In passing, the clonal architecture of early, pre-invasive lesions is examined, often with some surprising results.

Cytogenetic changes in benign proliferative and nonproliferative lesions of the breast

Cytogenetic analysis of short-term cultures from 69 cases of fibrocystic breast changes and 10 samples of normal mammary tissue revealed clonal chromosome aberrations in six fibrocystic lesions. All the histologically normal tissue samples had a normal karyotype. The frequency of cytogenetically abnormal cases seems to correlate with the degree of histopathologic changes of the tissue; nonproliferative lesions may have clonal chromosome alterations, but at a low frequency. Whether women with karyotypically altered fibrocystic "disease" have a higher risk of developing invasive breast cancer, compared with women without microscopically visible genetic anomalies in fibrocystic lesions, remains unknown.

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.

Monoclonality in fibroadenomas with complex histology and phyllodal features

Fibroadenoma is a common cause of benign breast masses in young women. These women have a slightly increased risk of subsequent breast cancer, particularly if their tumors have complex histologic patterns. We assessed monoclonality in fibroadenomas and correlated the results with histologic analysis. We performed a clonal analysis of 52 fibroadenomas from 43 patients using X-chromosome inactivation studies. The cases included fibroadenomas with complex and simple histology. Areas examined were predominantly stroma but epithelium was also present. DNA was isolated from paraffin-embedded tissue and was subjected to polymerase chain reaction amplification of the human androgen receptor gene with and without predigestion of the DNA with Hha 1. If a monoclonal process was identified, the epithelial and stromal components were subsequently microdissected and reanalyzed. 36/43 (83.7%) women were heterozygous. We studied 45 tumors in these 36 informative women. 1/20 (5% complex fibroadenomas and 1/25 (4%) simple fibroadenomas were monoclonal. The epithelial component of both monoclonal fibroadenomas was polyclonal. The one monoclonal simple fibroadenoma was also the only one with mixed features to contain a phyllodes component. In this case, monoclonality was found in the stroma of both the fibroadenoma and phyllodes regions. Monoclonality has been previously associated with phyllodes phenotype, but not with fibroadenomas, except for 3 fibroadenomas that recurred as phyllodes tumor. We report that monoclonality may also be seen occasionally in complex fibroadenomas, and was found in a tumors with mixed fibroadenoma/phyllodes features without clinical recurrence for 4 years.

Two cases of fibrocystic breast disease with polysomy 18 as the sole clonal cytogenetic abnormality

In the present study, we describe the occurrence of numerical alterations of chromosome 18 in two cases of benign fibrous/fibrocystic tumors of the breast, both of which were studied by conventional cytogenetic investigations and one of which was additionally tested by fluorescence in situ hybridization with the use of an alphoid centromeric probe specific for chromosome 18. Case 1 showed a tetrasomy 18 in 2 of 33 metaphases as the only clonal chromosomal aberration. Case 2 revealed both trisomy and tetrasomy 18 as clonal alterations in metaphases and interphase nuclei.

The incidence of microsatellite instability and loss of heterozygosity in fibroadenoma of the breast

A majority of studies have shown an increase in the risk of breast cancer among women previously diagnosed with fibroadenoma (FA). At present there is conflicting evidence whether some of the chromosome abnormalities frequently found in breast carcinoma, such as loss of heterozygosity (LOH), are already present in FAs and other types of benign breast disease and, if present, whether such abnormalities are associated with the observed increase in risk. Microsatellite instability (MSI) is also recognised as a marker of genetic damage and is thought to occur when there has been damage to the cell's mismatch repair (MMR) system. We have analysed 39 cases of FA obtained from paraffin-embedded tissue for the presence of MSI and LOH at 11 loci to determine if these types of genetic alterations occur in FA. The incidence of MSI and LOH found were 4 of 395 (1.0%) and 5 of 271 (1.8%) informative loci tested respectively. Approximately 8% of cases were positive for MSI and 10% were positive for LOH, with one specimen having multiple occurrences of both MSI and LOH. We conclude that these forms of genetic alteration do occur in FAs but that the incidence is low.

Chromosome imbalance at the 3p14 region in human breast tumours: high frequency in patients with inherited predisposition due to BRCA2

Our previous studies have indicated that genetic aberrations in the 3p14 region are more frequent in malignant tumours from hereditary breast cancer patients than sporadic breast cancers. The main purpose of this study was to test if BRCA2 susceptibility alleles contribute to imbalance in the 3p14 region. We mapped allelic imbalance at 3p14 in tumours from Icelandic sisters affected with breast cancer using a set of 10 microsatellite markers (tel-D3S1295-D3S1234-D3S1300-D3S1600-D3S1233+ ++-D3S1217-D3S1261-D3S1296-D3S1210- D3S1284-cen). The patients were of known carrier status with respect to the 999del5 mutation in BRCA2 which is the most common cause of hereditary breast cancer in Iceland. Of 103 patients, 32 in the group were mutation carriers. A high degree of imbalance was observed in tumours from BRCA2 mutation carriers, ranging from 44 to 88% for individual markers. This was significantly higher than the percentage of imbalance in tumours from non-carriers, where the frequency ranged from 25 to 43%. In both groups, we noted elevated 3p14 imbalance in patients with bilateral disease. Allelic imbalance was most commonly observed near the marker D3S1210 (3p14.1-p12) and the FHIT gene (3p21.1-p14.2) for both groups. We conclude that genomic aberrations in 3p14 are especially frequent in tumours with BRCA2 gene defects, and suggest that this is caused by regional loss of chromosome stability rather than selection.

Cytogenetic findings in phyllodes tumors of the breast: karyotypic complexity differentiates between malignant and benign tumors

Clonal karyotypic abnormalities were detected in short-term cell cultures from six phyllodes tumors of the breast. Whereas all five benign tumors had simple chromosomal changes, the highly malignant one had a near-triploid stemline, indicating that karyotypic complexity is a marker of malignancy in phyllodes tumors. Interstitial deletions of the short arm of chromosome 3, del(3)(p12p14) and del(3)(p21p23),were the only aberrations in two benign tumors. Cytogenetic polyclonality was detected in three benign tumors: two had cytogenetically unrelated clones, whereas the third had three different, karyotypically related cell populations as evidence of clonal evolution. The finding of clonal chromosome abnormalities in both the epithelial and connective tissue components of the phyllodes tumors indicates that they are genuinely biphasic, that is, that both components are part of the neoplastic parenchyma.

Fluorescence in situ hybridization of old G-banded and mounted chromosome preparations

An improved method for fluorescence in situ hybridization (FISH) investigation of old, previously G-banded, mounted chromosome preparations with chromosome specific painting probes and centromere-specific probes is described. Before hybridization, the slides are incubated in xylene until the coverslips detach spontaneously; any mechanical manipulation will jeopardize the results. The success of chromosome painting is improved by excluding the regular RNase treatment step prior to hybridization. Additional changes compared with standard FISH protocols are that the 2 x SSC step is omitted, that the amount of added probe is increased approximately 2.5 times, and that the amplification of signals is performed twice. The applicability of the method, which allows double painting with two differently labeled probes using two differently fluorescing colors, was tested on 11 cases involving different chromosome abnormalities and different types of material, including short-term cultures of epithelial and mesenchymal tumors, blood, leukemic bone marrow, and long-term cultures of a cell line derived from an epithelial tumor. Success was achieved even with chromosome preparations that were several years old.

A gene dosage effect is responsible for high overexpression of the MUC1 gene observed in human breast tumors

Alterations of the entire long arm of chromosome 1 are the most consistent cytogenetic abnormalities found in human breast carcinoma. Overexpression of a large number of genes, because of acquisition of additional copies of one arm or a whole chromosome, is one possible cause of the imbalance in cell metabolism. To investigate the existence of such a gene dosage effect in breast cancer, we chose to study the MUC1 mucin gene located at 1q21-q24. This gene is highly expressed in breast tumors, but the genetic mechanism for its ectopic overexpression is not clearly known. Thirty-two human primary breast tumors were examined, by Southern blot DNA and northern blot RNA analyses, for allelic dosage and expression of the MUC1 gene. A correlation was found between acquisition of additional copies of MUC1 gene and high mRNA levels (p < 0.0001). These results identify a genetic mechanism responsible for MUC1 gene overexpression and support the hypothesis that a gene dosage effect of the long arm of chromosome 1 may be involved in the pathogenesis of breast cancer.

Clinical significance of cytogenetic findings in solid tumors

Chromosome analysis of solid tumors is becoming an increasingly useful tool to help establish a correct diagnosis and to provide prognostically important information. Characteristic karyotypic patterns in terms of degree of cytogenetic complexity and type of nonrandom abnormalities may help to distinguish neoplasia from a nonneoplastic lesion and to differentiate between a benign and a malignant tumor. More importantly, the presence of a specific or pathognomonic change may confirm or refute a suspected diagnosis, provide an alternative, unsuspected diagnosis, and trace the origin of a metastasis. Presently, specific cytogenetic abnormalities may be of substantial, and sometimes decisive, help in four groups of differential diagnostic dilemmas: (1) Benign vs. malignant epithelial tumors of the kidney, thyroid gland, salivary glands, and ovary; (2) Benign vs. malignant mesenchymal tumors of adipose and muscle tissue; (3) Differentiation between various malignant bone and soft tissue tumors: and (4) Diagnosis of undifferentiated small-cell round-cell tumors. In addition to the diagnostic value, karyotypic findings may provide prognostic information. Thus, the presence of an abnormal clone and/or complex rearrangements is a poor prognostic sign in, e.g., carcinomas of the ovary, prostate, bladder, colon, and pancreas. Furthermore, characteristic cytogenetic aberrations are now known to be valuable prognostic parameters in malignant melanoma, malignant fibrous histiocytoma, germ cell tumors, neuroblastoma, and squamous cell carcinoma of the head and neck region. Many of the correlation analyses are preliminary, but they all point in the same direction, namely that cytogenetic studies will soon play the same essential role in the management of patients with solid tumors as they do today in hematologic oncology.

Cytogenetic polyclonality in tumors of the breast

Cytogenetically unrelated clones are found in half of all carcinomas of the breast and also in the epithelial fraction of many benign breast tumors. The chromosomal aberrations thus detected are clearly nonrandom and appear to be the same as those often seen in other tumors as sole karyotypic anomalies. Clonal chromosome abnormalities are not found in histologically normal breast tissue. Cytogenetically unrelated clones may be found in both primary tumors and secondary lesions, be it within the same breast (multifocal carcinomas), in the contralateral breast (bilateral carcinomas), or in lymph node or other metastases. The aberrations are present in topologically separate tumor domains and may confer on the cells that harbor them different types of cancer-specific behavior, such as the ability to metastasize and invade locally. Whereas the available evidence thus strongly indicates that the cells carrying clonal karyotypic aberrations all are part of the neoplastic parenchyma, it is less certain whether cytogenetic polyclonality actually signifies a multicellular tumor origin, although we think that this is the explanation that best accommodates the cytogenetic data. But even if it should eventually be shown that the seemingly unrelated clones have some submicroscopic tumorigenic mutation in common, the observed karyotypic heterogeneity is remarkable and goes far beyond what one has become accustomed to from most other tumor types. To understand how the various clones interact during mammary carcinogenesis will be a major task in future breast cancer research.

Microsatellite alterations indicating monoclonality in atypical hyperplasias associated with breast cancer

One model of breast tumorigenesis postulates a sequential evolution from normal to proliferative epithelium and eventually to neoplasia, but genetic data to support this progression have been limited. We wished to determine whether atypical hyperplasia (AH), a proliferative lesion conventionally classified and treated as benign, but associated with an increased risk of developing carcinoma, might show evidence of genetic abnormalities. Using the polymerase chain reaction (PCR), we examined DNA extracted from 12 separate AH lesions, from six breast cancer patients' paraffin-embedded tissue specimens, for alterations in microsatellite repeat sequences. Five of 12 AH lesions, from three of six patients, demonstrated alterations in microsatellite sequences in patterns indicating that the AH lesions are monoclonal or contain a substantial monoclonal component. We conclude that a subset of AH lesions from patients with breast cancer are characterized by monoclonal microsatellite alterations; therefore, they may already be neoplastic. This finding lends support to one postulated sequence of breast tumorigenesis and suggests that some type of genetic instability may play a role early in breast tumor development.