Karyotypic abnormalities in fibroadenomas of the breast

Biphasic, hyperdiploid breast tumors in children: a distinct entity?

BACKGROUND

The differentiation between a giant fibroadenoma and a phyllodes tumor can be a precarious diagnostic task. However, the distinction between the 2 lesions is important to make, especially since the latter can be malignant and consequently the prognoses differ.

PROCEDURE

We used various genetic approaches to study a breast tumor showing features of both entities in a 10-year-old girl with a congenital cerebral malformation and diabetes mellitus.

RESULTS

Cytogenetic analysis of cultured tumor cells from 3 different samples revealed a hyperdiploid karyotype: 50-54,XX,+5,+13,+17,+18,+19,+20,+21. High-resolution single nucleotide polymorphism array analysis not only confirmed the trisomies, but also revealed uniparental disomy (UPD) for chromosomes 10, 11, and 22. A consequence of UPD11 was a homozygous deletion in chromosome band 11p15 affecting the PARVA gene; this gene was hemizygously lost in constitutional DNA. Extended analysis of the family revealed that the deletion was inherited, but it did not segregate with breast tumors or congenital malformations.

CONCLUSIONS

Combined with the literature data, the findings in the present case strongly suggest that biphasic tumors with high hyperdiploid karyotypes constitute a distinct clinicomorphologic subgroup of benign breast tumors, being particularly common among young children.

Shattered and stitched chromosomes-chromothripsis and chromoanasynthesis-manifestations of a new chromosome crisis?

Chromothripsis (chromosome shattering) has been described as complex rearrangements affecting single chromosome(s) in one catastrophic event. The chromosomes would be "shattered" and "stitched together" during this event. This phenomenon is proposed to constitute the basis for complex chromosomal rearrangements seen in 2-3% of all cancers and in ∼ 25% of bone cancers. Here we discuss chromothripsis, the use of this term and the evidence presented to support a single catastrophic event that remodels the genome in one step. We discuss why care should be taken in using the term chromothripsis and what evidence is lacking to support its use while describing complex rearrangements.

Genomic alterations in histopathologically normal breast tissue from BRCA1 mutation carriers may be caused by BRCA1 haploinsufficiency

Multiple biopsies of normal breast tissue from 10 BRCA1 mutation carriers have been analyzed using array-based comparative genomic hybridization. Normal breast tissue from five age-matched control subjects without a family history of breast cancer was included for reference purposes. We repeatedly found multiple low copy number aberrations at a significantly higher frequency in histopathologically normal tissue from BRCA1 mutation carriers than in normal control tissue. Some of these aberrations were similar across samples from different patients and linked to biological functions such as transcriptional regulation and DNA binding. We also observed a high degree of genomic heterogeneity between samples from the same patient, suggestive of tissue heterogeneity and etiological clonality in the breast epithelium. We show that neither loss of heterozygosity nor promoter methylation of the wild-type BRCA1 allele is the predominant mechanistic origin of the observed genomic instability. Instead, we propose that haploinsufficiency of BRCA1 might be the underlying cause responsible for initiation of breast cancer in these predisposed women, making cells vulnerable to mitotic recombination. We also propose that loss of ERalpha expression is preceded by genetic instability in the initiation of BRCA1-dependent tumorigenesis, indicating that the breast epithelium of BRCA1 mutation carriers may initially be estrogen-responsive. Our results imply that genomic instability instigated by BRCA1 haploinsufficiency may be required for breast cancer initiation in BRCA1 mutation carriers. Finding molecular markers of tumor initiation and progression, for the potential use in early disease detection, may be of great clinical importance for the improved management of at-risk women.

Multicolour-banding fluorescence in situ hybridisation (mbanding-FISH) to identify recurrent chromosomal alterations in breast tumour cell lines

Recurrent chromosome breakpoints in tumour cells may point to cancer genes, but not many have been molecularly characterised. We have used multicolour-banding fluorescence in situ hybridisation (mbanding-FISH) on breast tumour cell lines to identify regions of chromosome break created by inversions, duplications, insertions and translocations on chromosomes 1, 5, 8, 12 and 17. We delineate a total of 136 regions of break, some of them occurring with high frequency. We further describe two examples of dual-colour FISH characterisation of breakpoints, which target the 1p36 and 5p11–12 regions. Both breaks involve genes whose function is unknown to date. The mbanding-FISH strategy constitutes an efficient first step in the search for potential cancer genes.

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.

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.

Chromosome analysis in 31 cases of benign and malignant breast tumors: a study in Brazil

Cultures of 31 breast tumors, being 20 carcinomas and 11 benign lesions, were cytogenetically analysed. Clonal chromosome aberrations were detected in 16 carcinomas and in 4 benign lesions. Nine carcinomas and 2 benign lesions had multiple cytogenetically unrelated and related clones, whereas a single abnormal clone was observed in 7 carcinomas and in 2 benign lesions. Polyploid clones were found in 7 carcinomas and in 2 benign lesions. The presence of clonal chromosome aberrations and polyploid cells was not associated with the clinicopathologic parameters tested. Carcinomas had more clonal changes than benign lesions (p = 0.031), showing that cytogenetic features are of diagnostic value and that different chromosome anomalies might have different pathogenetic and prognostic significance.

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.

Cytogenetic description of breast fibroadenomas: alterations related solely to proliferation?

Twelve breast fibroadenomas were analyzed cytogenetically and only four were found to have clonal alterations. The presence of chromosomal alterations in fibroadenomas must be the consequence of the proliferating process and must not be related to the etiology of this type of lesion. In contrast, the few fibroadenomas that exhibit chromosomal alterations are likely to be those presenting a risk of neoplastic transformation. Clonal numerical alterations involved chromosomes 8, 18, 19, and 21. Of the chromosomal alterations found in the present study, only monosomy of chromosomes 19 and 21 has been reported in breast fibroadenomas. The loss of chromosome 21 was the most frequent alteration found in our sample. The study of benign proliferations and their comparison with chromosome alterations in their malignant counterparts ought to result in a better understanding of the genes acting on cell proliferation alone, and of the genes that cause these cells to exhibit varied behaviors such as recurrences, spontaneous regression and fast growth.

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.

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.

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.

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.

Comparative allelotyping of the short arm of human chromosome 3 in epithelial tumors of four different types

Comparative allelotyping of the short arm of human chromosome 3 (3p) in four types of epithelial carcinomas was performed using an identical set of polymorphic markers. In total, 117 samples of non-papillary renal cell carcinoma (RCC), non-small cell lung carcinoma (NSCLC), carcinoma of uterine cervix (CC), and breast carcinoma (BC) were screened for loss of heterozygosity (LOH) with 10 di-, tri- and tetrameric markers covering nine bands of 3p. High LOH frequencies were detected in at least one locus: RCC (36/43, 84%), BC (20/26, 77%), NSCLC (16/24, 67%), and CC (15/24, 62%). Small interstitial deletions prevailed in BC and CC whereas large continuous and discontinuous deletions were mainly found in RCC and NSCLC. Different epithelial tumors displayed unique LOH profiles with partial overlaps in 3p26.1, 3p21.31, and 3p13. The overlap around D3S2409 (3p21.31) appeared common for RCC, BC and CC.

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.

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.

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.