Cytogenetic polyclonality in tumors of the breast

Advancements in Understanding the Hide-and-Seek Strategy of Hibernating Breast Cancer Cells and Their Implications in Oncology from a Broader Perspective: A Comprehensive Overview

Despite recent advancements in technology, breast cancer still poses a significant threat, often resulting in fatal consequences. While early detection and treatments have shown some promise, many breast cancer patients continue to struggle with the persistent fear of the disease returning. This fear is valid, as breast cancer cells can lay dormant for years before remerging, evading traditional treatments like a game of hide and seek. The biology of these dormant breast cancer cells presents a crucial yet poorly understood challenge in clinical settings. In this review, we aim to explore the mysterious world of dormant breast cancer cells and their significant impact on patient outcomes and prognosis. We shed light on the elusive role of the G9a enzyme and many other epigenetic factors in breast cancer recurrence, highlighting its potential as a target for eliminating dormant cancer cells and preventing disease relapse. Through this comprehensive review, we not only emphasise the urgency of unravelling the dynamics of dormant breast cancer cells to improve patient outcomes and advance personalised oncology but also provide a guide for fellow researchers. By clearly outlining the clinical and research gaps surrounding dormant breast cancer cells from a molecular perspective, we aim to inspire further exploration of this critical area, ultimately leading to improved patient care and treatment strategies.

Discordance of Biomarker Expression Profile between Primary Breast Cancer and Synchronous Axillary Lymph Node Metastasis in Preoperative Core Needle Biopsy

Background: Breast cancer (BC) is a heterogeneous disease made up of clones with different metastatic potential. Intratumoral heterogeneity may cause metastases to show divergent biomarker expression, potentially affecting chemotherapy response. Methods: We investigated the immunohistochemical (IHC) and FISH profile of estrogen receptors (ER), progesterone (PR) receptors, Ki67, and HER2 in a series of BC-matched primary tumors (PTs) and axillary lymph node (ALN) metastases in pre-operative core needle biopsies (CNBs). Phenotypical findings were correlated to morphological features and their clinical implications. Results: Divergent expression between PTs and ALNs was found in 10% of the tumors, often involving multiple biomarkers (12/31, 39%). Most (52%) displayed significant differences in ER and PR staining. HER2 divergences were observed in almost three-quarters of the cases (23/31, 74%), with five (16%) switching from negativity to overexpression/amplification in ALNs. Roughly 90% of disparities reflected significant morphological differences between PTs and ALN metastases. Less than half of the discrepancies (12/31, 39%) modified pre/post-operative treatment options. Conclusions: We observed relevant discrepancies in biomarker expression between PTs and metastatic ALNs in a noteworthy proportion (10%) of preoperative BC CNBs, which were often able to influence therapies. Hence, our data suggest routine preoperative assessment of biomarkers in both PTs and ALNs in cases showing significant morphological differences.

Primary tumor resection for initially staged IV breast cancer: An emphasis on programmed death-ligand 1 expression, promoter methylation status, and survival

Conventional therapy modalities for advanced breast cancer are problematic, whereas checkpoint blockade immunotherapy has been considered as a promising approach. This study aims to determine programmed death-ligand 1 (PD-L1) expression and methylation status of PD-L1 promoter in primary tumor tissue and metastatic foci of patients with stage IV breast cancer.Clinicopathological data and survival rates of 57 breast cancer patients, who were initially staged IV, and operated for intact tumors, were retrospectively analyzed. Immunohistochemical analysis of PD-L1 using 57 primary tumors, 33 paired metastatic lymph nodes, and 14 paired distant metastases was performed. Additionally, the methylation rate of the PD-L1 gene promoter region was determined with real-time polymerase chain reaction (PCR) analysis in 38 samples.Overall PD-L1 expression in primary tumors was 23.1% (12/52). PD-L1 positivity was reduced in lymph nodes by 15.2% (5/33) and in distant metastases by 21.4% (3/14). PD-L1 expression diverged between primary and metastatic foci in a subset of cases (18.2% for lymph node and 33.3% for distant metastasis). In general, the PD-L1 promoter was not methylated, and mean methylation rates were low (min. 0%-max. 21%). We observed no correlation between PD-L1 expression, promoter methylation, and survival.Neither the expression nor the methylation status of PD-L1 in patients, who were presented with stage IV breast cancer and operated for an intact primary tumor, had a statistically significant relation with survival. Discordance in PD-L1 expression between primary tumor and metastasis should be considered during pathological and clinical management of patients who would undergo checkpoint blockade therapy.

Profiles of brain metastases: Prioritization of therapeutic targets

We sought to compare the tumor profiles of brain metastases from common cancers with those of primary tumors and extracranial metastases in order to identify potential targets and prioritize rational treatment strategies. Tumor samples were collected from both the primary and metastatic sites of nonsmall cell lung cancer, breast cancer and melanoma from patients in locations worldwide, and these were submitted to Caris Life Sciences for tumor multiplatform analysis, including gene sequencing (Sanger and next-generation sequencing with a targeted 47-gene panel), protein expression (assayed by immunohistochemistry) and gene amplification (assayed by in situ hybridization). The data analysis considered differential protein expression, gene amplification and mutations among brain metastases, extracranial metastases and primary tumors. The analyzed population included: 16,999 unmatched primary tumor and/or metastasis samples: 8,178 nonsmall cell lung cancers (5,098 primaries; 2,787 systemic metastases; 293 brain metastases), 7,064 breast cancers (3,496 primaries; 3,469 systemic metastases; 99 brain metastases) and 1,757 melanomas (660 primaries; 996 systemic metastases; 101 brain metastases). TOP2A expression was increased in brain metastases from all 3 cancers, and brain metastases overexpressed multiple proteins clustering around functions critical to DNA synthesis and repair and implicated in chemotherapy resistance, including RRM1, TS, ERCC1 and TOPO1. cMET was overexpressed in melanoma brain metastases relative to primary skin specimens. Brain metastasis patients may particularly benefit from therapeutic targeting of enzymes associated with DNA synthesis, replication and/or repair.

Clinical Significance of Subtype Classification in Metastatic Lymph Nodes of Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy

Background

Neoadjuvant chemotherapy has been increasingly utilized in the treatment of breast cancer patients. However, there are no established surrogate markers predicting the response to subsequent adjuvant therapy and clinical outcome of patients. In particular, whether primary or lymph nodes metastasis should be evaluated for these analyses has remained unknown. Therefore, in this study, we first evaluated the differences in biomarkers between primary and metastatic cancer tissues in the patients undergoing neoadjuvant chemotherapy. We then correlated the findings with the clinical outcomes of these patients.

Methods

We examined 49 patients receiving neoadjuvant chemotherapy and subsequent surgery with lymph node metastasis. Estrogen receptor (ER), progesterone receptor (PgR), human epidermal growth factor receptor 2 (HER2) and Ki-67 were all immunohistochemically evaluated in core needle biopsy samples from primary and metastatic tumors following chemotherapy.

Results

No statistically significant differences in these markers were detected between the primary tumor and metastatic lymph nodes following therapy, but the Ki-67 labeling index was significantly higher in metastatic lymph nodes than in primary tumor (p = 0.017). The patients associated with luminal A type carcinoma in their lymph nodes following chemotherapy demonstrated significantly better clinical outcomes (disease-free survival: p = 0.0045, overall survival: p = 0.0006) than those who were not.

Conclusion

These data indicate that subtype classification following chemotherapy, in the metastatic lymph nodes rather than primary tumor could predict long-term outcomes of patients undergoing neoadjuvant chemotherapy.

Breast cancer with brain metastases: clinicopathologic features, survival, and paired biomarker analysis

BACKGROUND

The aim of this study was to describe clinicopathologic features of patients with breast cancer brain metastasis (BCBM); to evaluate survival after diagnosis of BCBM; and to compare estrogen receptor (ER), progesterone receptor (PR), and HER2 expression in the paired primary and brain tumors.

MATERIALS AND METHODS

We identified 140 consecutive patients who underwent craniotomy for BCBM (either for diagnostic purpose or with therapeutic intent) at the University of Texas MD Anderson Cancer Center between 2002 and 2009.

RESULTS

Most patients had invasive ductal histology (91%), grade 3 tumors (67%), and positive axillary lymph node (64%). Of the tumors, 56% were ER-negative, 62% were PR-negative, 44% were HER2-positive, and 28% were triple negative (TN). Brain metastasis (BM) was solitary in 51% of patients. Median interval from breast cancer diagnosis to BM was 46 months; median survival after BM was 14.1 months. In the univariate analysis, younger age, solitary brain metastasis, and ER or PR positivity in the breast tumors were associated with longer survival. There was a statistical trend toward increased survival in HER2-positive patients compared with HER2-negative patients (18 vs. 11 months). In the multivariate analysis, predictors for longer survival included younger age, solitary brain lesion, and HER2 positivity in the breast cancer. Biomarkers were evaluated in paired primary and brain tumors in 35 patients for ER status, 34 for PR status, and 36 for HER2 status. Discordant rates were 28% for ER, 20% for PR, and 3% for HER2.

CONCLUSION

Compared with unselected breast cancer patients at the same institution, patients with breast cancer who had brain metastases had a higher proportion of hormone receptor-negative, HER2-positive, and TN tumors. Younger age, solitary brain lesion, and HER2 expression were independent predictors of better survival in patients with BCBM. HER2 status was highly concordant between the paired primary and brain tumors, whereas changes of ER and PR status occurred in a substantial proportion of the patients. These findings are important for making effective treatment decisions for patients with BCBM.

Role of positron emission tomography for the monitoring of response to therapy in breast cancer

This review considers the potential utility of positron emission tomography (PET) tracers in the setting of response monitoring in breast cancer, with a special emphasis on glucose metabolic changes assessed with (18)F-fluorodeoxyglucose (FDG). In the neoadjuvant setting of breast cancer, the metabolic response can predict the final complete pathologic response after the first cycles of chemotherapy. Because tumor metabolic behavior highly depends on cancer subtype, studies are ongoing to define the optimal metabolic criteria of tumor response in each subtype. The recent multicentric randomized AVATAXHER trial has suggested, in the human epidermal growth factor 2-positive subtype, a clinical benefit of early tailoring the neoadjuvant treatment in women with poor metabolic response after the first course of treatment. In the bone-dominant metastatic setting, there is increasing clinical evidence that FDG-PET/computed tomography (CT) is the most accurate imaging modality for assessment of the tumor response to treatment when both metabolic information and morphologic information are considered. Nevertheless, there is a need to define standardized metabolic criteria of response, including the heterogeneity of response among metastases, and to evaluate the costs and health outcome of FDG-PET/CT compared with conventional imaging. New non-FDG radiotracers highlighting specific molecular hallmarks of breast cancer cells have recently emerged in preclinical and clinical studies. These biomarkers can take into account the heterogeneity of tumor biology in metastatic lesions. They may provide valuable clinical information for physicians to select and monitor the effectiveness of novel therapeutics targeting the same molecular pathways of breast tumor.

HER2-positive breast cancer: ¹⁸F-FDG PET for early prediction of response to trastuzumab plus taxane-based neoadjuvant chemotherapy

PURPOSE

To investigate the value of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET/CT) to predict a pathological complete response (pCR) after neoadjuvant chemotherapy (NAC) in women with human epidermal growth factor receptor 2 (HER2)-positive breast cancer.

MATERIAL AND METHODS

Fifty-seven consecutive women with HER2-positive breast cancer, treated with trastuzumab plus taxane-based NAC, were prospectively included. Maximum Standardized Uptake Value of the primary tumor and axillary nodes were measured at baseline (PET₁.SUVmax) and after the first course of NAC (PET₂.SUVmax). Tumor metabolic volumes were assessed to determine Total Lesion Glycolysis (TLG). The tumor metabolic response (ΔSUVmax and ΔTLG) was calculated.

RESULTS

In univariate analysis, negative hormonal receptor status (p = 0.04), high tumor grade (p = 0.03), and low tumor PET₂.SUVmax (p = 0.001) were predictive of pCR. Tumor ΔSUVmax correlated with pCR (p = 0.03), provided that tumors with low metabolic activity at baseline were excluded. ΔTLG did not correlate with pCR. In multivariate analysis, tumor PET₂.SUVmax < 2.1 was the best independent predictive factor (Odds ratio =14.3; p = 0.004) with both negative and positive predictive values of 76 %. Although the metabolic features of the primary tumor did not depend on hormonal receptor status, both the baseline metabolism and early response of axillary nodes were higher if estrogen receptors were not expressed (p = 0.01 and p = 0.03, respectively).

CONCLUSION

In HER2-positive breast cancer, very low tumor residual metabolism after the first cycle of NAC (SUVmax < 2.1) was the main predictor of pCR. These results should be further explored in multicenter studies and incorporated into the design of clinical trials.

Intratumor diversity and clonal evolution in cancer--a skeptical standpoint

Clonal evolution in cancer is intimately linked to the concept of intratumor cellular diversity, as the latter is a prerequisite for Darwinian selection at the micro-level. It has been frequently suggested in the literature that clonal evolution can be promoted by an elevated rate of mutation in tumor cells, so-called genomic instability, the mechanisms of which are now becoming increasingly well characterized. However, several issues need clarification before the presumably complex relationship between mutation rate, intratumor diversity, and clonal evolution can be understood sufficiently well to translate into models that predict the course of tumor disease. In particular, it has to be clarified which of the proposed mechanisms for genomic instability that are able to generate daughter cells with sufficient viability to form novel clones, how clones with different genomic changes differ phenotypically from each other, and what the selective forces are that guide competition among diverse clones in different microenvironments. Furthermore, standardized measurements of mutation rates at the chromosome level, as well as genotypic and phenotypic diversity, are essential to compare data from different studies. Finally, the relationship between clonal variation brought about by genomic instability, on the one hand, and cellular differentiation hierarchies, on the other hand, should be explored to put genomic instability in the context of the tumor stem cell hypothesis.

Cytogenetic analysis of tumor clonality

All or almost all neoplasias subjected to systematic cytogenetic scrutiny have been found to harbor acquired chromosomal aberrations. The paradigm stemming from the study of hematopoietic malignancies and sarcomas is that cancers are of monoclonal origin (i.e., they have developed from a single transformed somatic progenitor) because all the neoplastic parenchyma cells share at least one primary chromosomal abnormality, with subsequent clonal evolution along the lines of Darwinian selection occurring among the various subclones carrying secondary aberrations. When carcinomas began to be studied more extensively by cytogenetic methods, however, sometimes many cytogenetically unrelated clones were found, in seeming contradiction to the monoclonal hypothesis. Also studies of multiple samples from the same patient led to a rethinking of what the cytogenetic evidence really revealed about tumor clonality, both in its early stages and during disease development. The observed cytogenetic heterogeneity in, for example, tumors of the breast and pancreas vastly surpasses that of leukemias, lymphomas, connective tissue tumors, or even most epithelial, including uroepithelial, tumors. Theoretical reasoning as well as the available experimental data we here review show that the clonal evolution of neoplastic cell populations follows either of four principal pathways: (1) initial monoclonality is retained throughout the entire course of the disease with no additional, secondary aberrations accrued as judged by karyotypic appearance; (2) tumorigenesis is monoclonal but additional aberrations develop with time leading to secondary clonal heterogeneity (clonal divergence); (3) polyclonal tumorigenesis exists from the beginning but is followed by an overall reduction in genomic complexity with time (clonal convergence) due to selection among cytogenetically unrelated clones during tumor progression, resulting in secondary oligo- or monoclonality; or (4) polyclonal tumorigenesis with early clonal convergence is followed by later clonal divergence due to the acquisition of additional cytogenetic changes by the clone(s) that survived during the middle phases of tumor progression. Further studies of individual tumor cells are necessary to elicit precise information about the cell-to-cell variability that exists in many, especially epithelial, neoplasms and which holds the key to a more profound understanding of the complex issue of tumor clonality during all stages of cancer development.

Microsatellite analysis in multistage carcinogenesis of esophageal squamous cell carcinoma from Chongqing in Southern China

In order to characterize the molecular events in the carcinogenesis of esophageal cancer and to identify biomarkers for the early detection of the disease, matched precancerous and cancerous tissues resected from 34 esophageal cancer patients in Chongqing of southern China were compared for the extent of loss of heterozygosity (LOH). Sixteen microsatellite markers on nine chromosome regions were used for the PCR-based LOH analysis. The overall frequency of LOH at the 16 microsatellite loci was significantly increased as the pathological status of the resection specimens changed from low-grade dysplasia (LGD) to high-grade dysplasia (HGD) and squamous cell carcinoma (SCC) (P < 0.001), indicating that tumorigenesis of the esophageal squamous epithelia is a progressive process involving accumulative changes of LOH. A total of eight markers showed LOH in the LGD samples, suggesting that these loci may be involved in the early-stage tumorigenesis of esophageal squamous cell carcinoma (ESCC) and that LOH analysis at these loci may help improve the early detection of this disease. In addition, heterozygosity was regained at four loci in the SCC samples of four patients compared with the HGD samples, suggesting the possibility of genetic heterogeneity in the tumorigenesis of esophageal cancer.

Cytogenetic polyclonality of breast carcinomas: association with clinico-pathological characteristics and outcome

Routinely used prognostic factors fail to predict clinical outcome in a significant proportion of breast cancer patients, implying that they can not detect some important biological characteristics. Chromosomal changes have been described in breast carcinomas for many years but their significance is not clear. We compared chromosomal changes with clinico-pathological characteristics and clinical outcome in 203 breast cancer patients with a follow-up of 9-18 years. Combining data from classical cytogenetics and flow cytometry revealed chromosomal abnormalities in 142 cases (70%). Of these, 51 (35.9%) contained two or more cytogenetically abnormal clones. Polyclonality was significantly associated with poor breast-cancer-specific survival (P = 0.03) within 5 years, independent of tumor size, lymph node metastases, and hormone receptors. Specific changes were similar to those previously described, but a new finding was a significant association between del 3p12p21 and poor survival. Polyclonality was significantly associated with TP53-mutations but not with a germline BRCA2 mutation. Less than one third of the polyclonal samples were identified by flow cytometry alone. Cytogenetic changes were detected in 17 out of 114 samples from non-tumorous tissue (15%), two of them identical with a clone in the corresponding tumor. Several samples contained clearly unrelated clones within the tumor and outside, implying either multifocal origin or early divergence. In conclusion, the common deletion on Chromosome 3p12p21 was associated with poor clinical outcome. Chromosomal polyclonality is common in breast carcinomas and predicts poor survival. Polyclonality was poorly detected by one-sample flow cytometry. Multiple sampling might improve the detection rate.

Loss of heterozygosity analysis of microsatellites on multiple chromosome regions in dysplasia and squamous cell carcinoma of the esophagus

The objective of this study was to characterize the molecular events in the carcinogenesis of esophageal squamous cell carcinoma (ESCC) and to identify biomarkers for early detection of the disease. Matched precancerous and cancerous tissues resected from 34 esophageal cancer patients from Chongqing, southern China, were compared to evaluate the extent of loss of heterozygosity (LOH). Sixteen microsatellite markers on chromosome regions 3p, 4p, 5q, 8p, 9p, 9q, 11p, 13q and 17p were used for PCR-based LOH analysis. The overall frequency of LOH at the 16 microsatellite loci was significantly increased as the pathological status of the resection specimens changed from low-grade dysplasia (LGD) to high-grade dysplasia (HGD) and SCC (P<0.001). A total of 8 markers showed LOH in the LGD samples. In addition, heterozygosity was regained at 4 loci in the SCC samples of 4 patients, respectively, in comparison to the results for these loci in the HGD samples. The overall rate of LOH increased significantly with the deterioration of the lesions, indicating that tumorigenesis of the esophageal squamous epithelia is a progressive process involving accumulative changes in LOH. The 8 loci showing allelic loss in the LGD samples may be involved in the early-stage tumorigenesis of ESCC, and LOH analysis at these loci may help improve the early detection of this disease. Regain of heterozygosity found in certain patients suggests the possibility of genetic heterogeneity in the tumori-genesis of esophageal cancer.

ER, HER2, and TOP2A expression in primary tumor, synchronous axillary nodes, and asynchronous metastases in breast cancer

At recurrence of breast cancer, the therapeutic target is the metastases. However, it is current practice to base the choice of systemic treatment on the biomarker profile of the primary tumor. In the present study, confirmatory biopsies were obtained from suspected metastatic lesions and compared with the primary tumors with respect to ER, HER2, and TOP2A. In the prospective tissue-collection study, 81 patients had biopsy from a suspected relapse. Additional archived paired material was included, leaving a total of 119 patients with paired primary tumor, synchronous axillary nodes (available in 52 patients) and asyncronous metastases available for analysis. ER, HER2, and TOP2A expression of primary tumors, axillary nodes and metastases were re-analysed and determined centrally by immunohistochemistry, chromogenic in situ hybridization, and fluorescence in situ hybridization. Of the 81 patients with a biopsy from a suspected relapse, 65 (80%) were diagnosed with recurrent breast carcinoma, 3 (4%) were diagnosed with other malignancies, 6 (7%) had benign conditions, and in 7 (9%) patients the biopsy was non-representative. Discordance in ER, HER2, and TOP2A (aberration vs. normal) status between primary tumor and corresponding asynchronous metastasis was 12% (14/118), 9% (10/114), and 23% (17/75), respectively. There were no significant associations with biomarker discordance and prior adjuvant therapy, or location of biopsy. Expression of ER, HER2, and TOP2A displayed discordance with a sufficient frequency to emphasize the role of confirmatory biopsies from metastatic lesions in future management of recurrent breast cancer.

PIK3CA mutations may be discordant between primary and corresponding metastatic disease in breast cancer

PURPOSE

PIK3CA mutations are frequent in breast cancer and activate the PI3K/Akt pathway. Unexpectedly, PIK3CA mutation appears in general to be associated with better outcome. In a cohort of patients where both primary and metastatic lesions were available, the objective was to assess changes in PIK3CA mutations. We wished to discern whether selective pressures occur and the influence of PIK3CA mutation on time to recurrence.

EXPERIMENTAL DESIGN

Formalin-fixed paraffin-embedded tumor blocks were obtained from 104 patients with paired samples from primary tumors and corresponding asynchronous metastatic breast tumors. Samples were analyzed for PIK3CA mutations (exons 9 and 20) as well as immunohistochemical evaluation for PTEN, pAKT, Ki67, ER, and HER2.

RESULTS

PIK3CA mutation was detected in 45% of the primary tumors. Overall, there was a net gain in mutation in metastatic disease, to 53%; nonetheless, there were instances where metastases were wild type in patients with PIK3CA mutant primary tumors. Laser capture microdissection on a subset of cases revealed microheterogeneity for PIK3CA mutational status in the primary tumor. PIK3CA mutants overall showed a significantly longer time to first recurrence than wild type cases (P = 0.03).

CONCLUSION

PIK3CA mutations occur at high frequency in primary and metastatic breast cancer; these may not necessarily confer increased aggressiveness as mutants had a longer time to recurrence. Because PIK3CA status quite frequently changes between primary and metastatic disease, it emphasizes the necessity of assessing the PIK3CA status in the metastatic lesion for selection of PIK3CA inhibitor therapy.

Comparative study of the immunohistochemical detection of hormone receptor status and HER-2 expression in primary and paired recurrent/metastatic lesions of patients with breast cancer

Recent studies have shown some degrees of discordance in ER, PR and HER-2 immunohistochemical expression between primary and recurrent/metastatic lesions (RML). Analysis was made on 78 patients with MBC whose ER, PR and/or HER-2 status were known both on the tissue samples of primary and RML. Among the RML sites, 29.5% were locoregional, 70.5% were distant metastatic sites. Among 75 patients with known ER expression on both primary and RML, 36% (n = 27) showed discordance on ER expression. Among 72 patients with known PR expression on both primary and RML, 54.2% (n = 39) showed discordance on PR expression. Among 61 patients with known HER-2 expression on both primary and RML, 14.7% (n = 9) showed discordance on HER-2 expression. No differences were observed when we compared patients who have discordant ER and HER-2 status with patients who have concordant results between the primary tumor and paired RML with respect to site of biopsy (locoregional vs distant metastasis) and prior therapies (chemotherapy and endocrine therapy). As these discordant results make changes in treatment decision, a biopsy of the metastatic lesion could be recommended in patients with MBC when feasible. Larger series are needed to identify the potential effect of prior therapies and site of metastasis on discordant results.

Inferring tumor progression from genomic heterogeneity

Cancer progression in humans is difficult to infer because we do not routinely sample patients at multiple stages of their disease. However, heterogeneous breast tumors provide a unique opportunity to study human tumor progression because they still contain evidence of early and intermediate subpopulations in the form of the phylogenetic relationships. We have developed a method we call Sector-Ploidy-Profiling (SPP) to study the clonal composition of breast tumors. SPP involves macro-dissecting tumors, flow-sorting genomic subpopulations by DNA content, and profiling genomes using comparative genomic hybridization (CGH). Breast carcinomas display two classes of genomic structural variation: (1) monogenomic and (2) polygenomic. Monogenomic tumors appear to contain a single major clonal subpopulation with a highly stable chromosome structure. Polygenomic tumors contain multiple clonal tumor subpopulations, which may occupy the same sectors, or separate anatomic locations. In polygenomic tumors, we show that heterogeneity can be ascribed to a few clonal subpopulations, rather than a series of gradual intermediates. By comparing multiple subpopulations from different anatomic locations, we have inferred pathways of cancer progression and the organization of tumor growth.

Intratumoral Heterogeneity of HER2/neu in Breast Cancer?A Rare Event

HER2/neu is overexpressed in about 20% of invasive breast carcinomas. Numerous studies have shown that there is high level of concordance between the HER2/neu status of the primary breast cancer and the metastases of a given patient. Recently, changes in HER2/neu status with tumor progression have been reported, suggesting the possibility of an emerging different tumor clone. Little is known about intratumoral heterogeneity with regard to HER2/neu oncoprotein overexpression. We identified nine cases of invasive ductal carcinoma that showed intratumoral variation in HER2/neu oncoprotein expression by immunohistochemistry. This was confirmed by the intratumoral variation in the amplification status of the HER2/neu gene by fluorescence in situ hybridization and by chromogenic in situ hybridization. The results of this study suggest that some cases of primary breast carcinoma are heterogeneous in regard to HER2/neu gene amplification or protein overexpression. Heterogeneity of HER2/neu status in a tumor may be a rare event or underestimated. This phenomenon should be examined as it may contribute to a better understanding of the variation in therapeutic responses and the conflicting data in studies about the prognostic and predictive role of HER2/neu status in subsets of breast cancer patients.

Unlocking pathology archives for molecular genetic studies: a reliable method to generate probes for chromogenic and fluorescent in situ hybridization

Chromogenic (CISH) and fluorescent (FISH) in situ hybridization have emerged as reliable techniques to identify amplifications and chromosomal translocations. CISH provides a spatial distribution of gene copy number changes in tumour tissue and allows a direct correlation between copy number changes and the morphological features of neoplastic cells. However, the limited number of commercially available gene probes has hindered the use of this technique. We have devised a protocol to generate probes for CISH that can be applied to formalin-fixed, paraffin-embedded tissue sections (FFPETS). Bacterial artificial chromosomes (BACs) containing fragments of human DNA which map to specific genomic regions of interest are amplified with phi29 polymerase and random primer labelled with biotin. The genomic location of these can be readily confirmed by BAC end pair sequencing and FISH mapping on normal lymphocyte metaphase spreads. To demonstrate the reliability of the probes generated with this protocol, four strategies were employed: (i) probes mapping to cyclin D1 (CCND1) were generated and their performance was compared with that of a commercially available probe for the same gene in a series of 10 FFPETS of breast cancer samples of which five harboured CCND1 amplification; (ii) probes targeting cyclin-dependent kinase 4 were used to validate an amplification identified by microarray-based comparative genomic hybridization (aCGH) in a pleomorphic adenoma; (iii) probes targeting fibroblast growth factor receptor 1 and CCND1 were used to validate amplifications mapping to these regions, as defined by aCGH, in an invasive lobular breast carcinoma with FISH and CISH; and (iv) gene-specific probes for ETV6 and NTRK3 were used to demonstrate the presence of t(12;15)(p12;q25) translocation in a case of breast secretory carcinoma with dual colour FISH. In summary, this protocol enables the generation of probes mapping to any gene of interest that can be applied to FFPETS, allowing correlation of morphological features with gene copy number.

Multicolor fluorescence in situ hybridization characterization of cytogenetically polyclonal hematologic malignancies

Several different investigations and methodologies have provided data supporting a monoclonal origin of neoplasia. For example, the vast majority of neoplastic disorders are cytogenetically monoclonal. Occasionally, however, clones with unrelated karyotypic anomalies are found, as, for example, in approximately 2% of acute myeloid leukemias (AML), myelodysplastic syndromes (MDS), and chronic myeloproliferative disorders (CMD). Whether such a cytogenetic polyclonality represents a polyclonal origin or whether different clones share a submicroscopic primary change, indicating a monoclonal origin, remains to be elucidated. Our objective was to ascertain if cryptic aberrations can be found in cytogenetically polyclonal hematologic malignancies using multicolor fluorescence in situ hybridization (M-FISH). Fourteen AML, MDS, and CMD cases were investigated. In none of these was a cryptic aberration found, common to all subclones, although the karyotypes were revised in two AMLs and one MDS. Thus, all malignancies were still classified as polyclonal after the M-FISH analyses. Based on the present results, we conclude that M-FISH, in general, does not reveal primary cryptic aberrations supporting a monoclonal origin of cytogenetically polyclonal hematologic malignancies.

Global Protein Shotgun Expression Profiling of Proliferating MCF-7 Breast Cancer Cells

Protein expression becomes altered in breast epithelium during malignant transformation. Knowledge of these perturbations should provide insight into the molecular basis of breast cancer, as well as reveal possible new therapeutic targets. To this end, we have performed an extensive comparative proteomic survey of global protein expression patterns in proliferating MCF-7 breast cancer cells and normal human mammary epithelial cells using gel-free shotgun tandem mass spectrometry. Pathophysiological alterations associated with the malignant breast cancer phenotype were detected, including differences in the apparent levels of key regulators of the cell cycle, signal transduction, apoptosis, transcriptional regulation, and cell metabolism.

Molecular cytogenetic analysis of breast cancer: a combined multicolor fluorescence in situ hybridization and G-banding study of uncultured tumor cells

In six patients with breast cancer, uncultured tumor cells were investigated with G-banding and multicolor fluorescence in situ hybridization (M-FISH). A large number of numerical and structural aberrations could be analyzed. Among other structural abnormalities, reciprocal, hidden and complex translocations were found. Recurrent t(1;10) and t(6;16), not previously described, were identified, as well as t(15;22). The latter was also found in additional cases among our unpublished breast carcinomas. The significance of t(15;22) for breast cancer is discussed, taking into account also data drawn from the literature. Reciprocal translocations were a prominent feature in a pseudodiploid lobular carcinoma. Hidden translocations on 6p22-p24 were detected with M-FISH. Involvement of 6p22-p24 was observed in five cases. The analysis of various other translocations and different structural abnormalities revealed the following common breakpoints (according to frequency of involvement): 1p34-p36, 3p12-p13, 4p13-->q11, 14p11-->q11, 1q42, 8p11, 8q24, 10q22, 11q13, 11q23-q24, 13q13, and 18p10-p11. Loss of 3p and 1p34-p36-->pter and complete or partial loss of 13q and chromosome 17 were also found. With the combination of G-banding and M-FISH techniques, chromosome misclassification is avoided and the characterization of complex tumor karyotypes is more effective.

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.

Cytogenetic characterization of tumors of the vulva and vagina

Neoplasms of the vulva and vagina account for less than 5% of all female genital tract cancers. Squamous cell carcinoma (SCC) represents more than 70% of the cases in both locales, followed by melanoma, basal cell carcinoma, Paget's disease, and other carcinoma subtypes. Until recently, only few cases had been analyzed by chromosome banding techniques and karyotyped, and also the number subjected to molecular cytogenetic analysis remains low. To understand better the genetic changes harbored by the neoplastic cells in cancer of the vulva and vagina, we analyzed cytogenetically 51 such tumors, finding karyotypic abnormalities in 37. All tumors were analyzed by G-banding, sometimes supplemented by multicolor fluorescence in situ hybridization, and a subset of tumors was also analyzed by comparative genomic hybridization. The two cytogenetically abnormal cases of Paget's disease both had two clones, one with gain of chromosome 7 as the sole change, the other with loss of the X chromosome among, in one case, other aberrations. The four cytogenetically abnormal malignant melanomas (three of the vulva, one of the vagina) presented complex karyotypes with aberrations involving different chromosomes but most often chromosome 1, specifically 1p12-q41. In the 31 cytogenetically abnormal SCCs, different clonal karyotypic abnormalities were seen. Intratumor heterogeneity with multiple clones was observed in 11 cases. The clones were cytogenetically unrelated in eight tumors but related in three, indicating that in the latter clonal evolution had taken place from a single malignantly transformed cell. The main chromosomal imbalances were gains of, or from, chromosome arms 3q, 5p, 8q, 9q, and 19q, and loss from 11q. Breakpoint clusters were seen in 11q13-23, 2q22-35, and 19q13, as well as in the centromeres and pericentromeric bands of chromosomes 3, 8, 9, 13, 14, and 22.

Genetic variability in MCF-7 sublines: evidence of rapid genomic and RNA expression profile modifications

BACKGROUND

Both phenotypic and cytogenetic variability have been reported for clones of breast carcinoma cell lines but have not been comprehensively studied. Despite this, cell lines such as MCF-7 cells are extensively used as model systems.

METHODS

In this work we documented, using CGH and RNA expression profiles, the genetic variability at the genomic and RNA expression levels of MCF-7 cells of different origins. Eight MCF-7 sublines collected from different sources were studied as well as 3 subclones isolated from one of the sublines by limit dilution.

RESULTS

MCF-7 sublines showed important differences in copy number alteration (CNA) profiles. Overall numbers of events ranged from 28 to 41. Involved chromosomal regions varied greatly from a subline to another. A total of 62 chromosomal regions were affected by either gains or losses in the 11 sublines studied. We performed a phylogenetic analysis of CGH profiles using maximum parsimony in order to reconstruct the putative filiation of the 11 MCF-7 sublines. The phylogenetic tree obtained showed that the MCF-7 clade was characterized by a restricted set of 8 CNAs and that the most divergent subline occupied the position closest to the common ancestor. Expression profiles of 8 MCF-7 sublines were analyzed along with those of 19 unrelated breast cancer cell lines using home made cDNA arrays comprising 720 genes. Hierarchical clustering analysis of the expression data showed that 7/8 MCF-7 sublines were grouped forming a cluster while the remaining subline clustered with unrelated breast cancer cell lines. These data thus showed that MCF-7 sublines differed at both the genomic and phenotypic levels.

CONCLUSIONS

The analysis of CGH profiles of the parent subline and its three subclones supported the heteroclonal nature of MCF-7 cells. This strongly suggested that the genetic plasticity of MCF-7 cells was related to their intrinsic capacity to generate clonal heterogeneity. We propose that MCF-7, and possibly the breast tumor it was derived from, evolved in a node like pattern, rather than according to a linear progression model. Due to their capacity to undergo rapid genetic changes MCF-7 cells could represent an interesting model for genetic evolution of breast tumors.

Genetic heterogeneity of single disseminated tumour cells in minimal residual cancer

BACKGROUND

Because cancer patients with small tumours often relapse despite local and systemic treatment, we investigated the genetic variation of the precursors of distant metastasis at the stage of minimal residual disease. Disseminated tumour cells can be detected by epithelial markers in mesenchymal tissues and represent targets for adjuvant therapies.

METHODS

We screened 525 bone-marrow, blood, and lymph-node samples from 474 patients with breast, prostate, and gastrointestinal cancers for single disseminated cancer cells by immunocytochemistry with epithelial-specific markers. 71 (14%) of the samples contained two or more tumour cells whose genomic organisation we studied by single cell genomic hybridisation. In addition, we tested whether TP53 was mutated. Hierarchical clustering algorithms were used to determine the degree of clonal relatedness of sister cells that were isolated from individual patients.

FINDINGS

Irrespective of cancer type, we saw an unexpectedly high genetic divergence in minimal residual cancer, particularly at the level of chromosomal imbalances. Although few disseminated cells harboured TP53 mutations at this stage of disease, we also saw microheterogeneity of the TP53 genotype. The genetic heterogeneity was strikingly reduced with the emergence of clinically evident metastasis.

INTERPRETATION

Although the heterogeneity of primary tumours has long been known, we show here that early disseminated cancer cells are genomically very unstable as well. Selection of clonally expanding cells leading to metastasis seems to occur after dissemination has taken place. Therefore, adjuvant therapies are confronted with an extremely large reservoir of variant cells from which resistant tumour cells can be selected.

Hyperplasia versus adenoma in endocrine tissues: are they different?

The traditional view holds that hyperplasia of endocrine glands is secondary to oversecretion of a trophic hormone. However, in most cases, the mechanism underlying this growth is the spontaneous proliferation of benign neoplasias. Pathologists still depend on subtle morphological criteria to delineate and further classify these tumours. Owing to their variable architecture, a bewildering nomenclature has emerged for these tumours, exemplified by the many names applied to the goitrous thyroid gland: hyperplasia, adenomatous goitre, adenomatoid nodules, benign nodular thyroid disease, adenoma, etc. This article reviews the evidence suggesting that: (1) the varied types of benign neogeneration of endocrine tissue, the spectrum of which ranges from 'simple hyperplasia' to 'true adenoma', involve the same process; (2) even clonality of a growing lesion cannot distinguish hyperplasia from neoplasia; and (3) the basic processes in both cases are not different from those that cause benign tumours in other organs.

Precise microdissection of human bladder carcinomas reveals divergent tumor subclones in the same tumor

BACKGROUND

Human bladder carcinoma is thought to arise from a field change that affects the entire urothelium. Whether independently transformed urothelial cell populations exist in the same patient is uncertain.

METHODS

We studied the clonality of urinary bladder carcinoma in 18 female patients who underwent cystectomy for urothelial carcinoma. None had multiple tumors. Tumor samples were obtained from different areas of the same tumor. Sixty-seven tumor samples were analyzed. Tumor genomic DNA was microdissected and extracted from formalin-fixed, paraffin-embedded slides. The clonality of urothelial tumors was evaluated on the basis of a polymorphism of the X chromosome-linked human androgen receptor gene (HUMARA) locus. The technique is dependent on digestion of DNA with the methylation-sensitive restriction enzyme HhaI, polymerase chain reaction (PCR) amplification of HUMARA locus, and detection of methylation of this locus. With this method, only the methylated HUMARA allele is selectively amplified by PCR.

RESULTS

Eleven of 18 patients were informative. Nonrandom inactivation of the X chromosome was found in 9 of the 11 informative patients (82%). Seven patients showed different patterns of nonrandom X chromosome inactivation for tumor samples obtained from different regions of the same tumor. Two patients showed the same pattern of nonrandom X chromosome inactivation in all samples.

CONCLUSIONS

Some muscle-invasive urothelial carcinomas may arise from independently transformed progenitor urothelial cells, supporting the "field effect" theory for bladder 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.

Are some breast carcinomas polyclonal in origin?

This editorial comments on the important study by Going et al. published in the present issue of the Journal [1]. Using a molecular genetic assay based on the X-chromosome inactivation principle, they found that 4 out of 12 breast carcinomas examined exhibited what the authors call "clonal mosaicism" that is, two or more monoclonal samples were mosaic (polyclonal) in respect of X chromosome inactivation between separate, morphologically homogeneous tumour areas. The authors very carefully discuss potential methodological errors that could have led to this surprising finding, which seems to run counter to the almost unanimously held conviction that carcinomas are monoclonal in origin, but none of these potential errors would explain the results. As often in such situations, the authors prudently state that further studies using independent analytical techniques are necessary to find out whether a significant proportion of mammary carcinomas are indeed polyclonal. However, there already exists a substantial body of evidence from cytogenetic studies of breast cancers indicating that many of them are polyclonal. Although there is still room for interpretation and some doubt remains as to exactly which role should be ascribed to the observed clonal heterogeneity in our models of carcinogenesis, it seems obvious that more attention than before ought to be paid to this now well documented fact.

Return of de-differentiation: why cancer is a developmental disease

Many important advances have been made in the phenotypic and genetic characterization of malignant tumors since the publication of Peter Nowell's seminal article on the origin of cancer, but there has been no consistent effort to incorporate this wealth of knowledge into a general model of carcinogenesis. Current theoretical discussions on cancer are frequently dominated by attempts to categorize genetic alterations and phenotypic characteristics and establish correspondences between them. In this article, I argue, on the basis of recent data as well as "old" observations, that a developmental error leading to the acquisition of a unique cell character (de-differentiation) underlies all phenotypic characteristics of cancer cells and discuss how this notion can be reconciled with Nowell's model of carcinogenesis as a microevolutionary process into an updated theoretical description of cancer.

Cytogenetic heterogeneity and clonal evolution in synchronous bilateral breast carcinomas and their lymph node metastases from a male patient without any detectable BRCA2 germline mutation

Two synchronous bilateral breast carcinomas and their matched lymph node metastases from a 70-year-old man were cytogenetically analyzed. All four tumors were near-diploid, and except for the primary tumor from the right breast, had a 45,X,-Y clone in common. The loss of the Y chromosome was, however, common to all four tumors, whereas metaphase cells from peripheral blood lymphocytes showed a normal 46, XY chromosome complement. The primary tumor from the right breast was monoclonal, with loss of the Y chromosome and gain of 1q, whereas its metastasis had two related clones: the 45,X,-Y clone, and the other a more complex version of the clone in the primary tumor, with inv(3), -14, and del(16)(q13) as additional changes. The primary tumor from the left breast was polyclonal with three unrelated clones: 45,X,-Y/45,XY,-18/47,XY,+20, two of which were present in its metastasis. DNA flow cytometric studies showed diploidy for both primary tumors. No mutation in the BRCA2 gene was found on analysis of DNA from peripheral blood lymphocytes. The present findings show that del(16)(q13) is a recurrent finding among male breast carcinomas and that some of the primary cytogenetic abnormalities, as well as the pattern of chromosomal changes during the progression of sporadic breast carcinoma in the male, are similar to those in the female. In addition, the loss of the Y chromosome in the tumors but not in peripheral blood lymphocytes, suggests a possible role for this abnormality in the pathogenesis of male breast carcinoma.

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.

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.

Hex1: a new human Rad2 nuclease family member with homology to yeast exonuclease 1

Nucleolytic processing of chromosomal DNA is required in operations such as DNA repair, recombination and replication. We have identified a human gene, named HEX1 forhumanexonuclease 1, by searching the EST database for cDNAs that encode a homolog to the Saccharomyces cerevisiae EXO1 gene product. Based on its homology to this and other DNA repair proteins of the Rad2 family, most notably Schizosaccharomyces pombe exonuclease 1 (Exo1), Hex1 presumably functions as a nuclease in aspects of recombination or mismatch repair. Similar to the yeast proteins, recombinant Hex1 exhibits a 5'-->3' exonuclease activity. Northern blot analysis revealed that HEX1 expression is highest in fetal liver and adult bone marrow, suggesting that the encoded protein may operate prominently in processes specific to hemopoietic stem cell development. HEX1 gene equivalents were found in all vertebrates examined. The human gene includes 14 exons and 13 introns that span approximately 42 kb of genomic DNA and maps to the chromosomal position 1q42-43, a region lost in some cases of acute leukemia and in several solid tumors.

Cytogenetic and molecular genetic demonstration of polyclonality in an acinic cell carcinoma

The paradigm that human malignancies are monoclonal has been questioned during recent years by the finding of unrelated, cytogenetically aberrant clones in short-term cultures from certain tumour types, notably carcinomas of the breast, skin and upper aerodigestive tract. In order to analyse whether cytogenetically unrelated clones are also unrelated at the molecular level, we analysed the X-chromosome inactivation status in cell cultures from a cytogenetically highly polyclonal acinic cell carcinoma of the parotid gland. By using cell cultures dominated by a single abnormal clone, obtained through in vitro culturing for 3-5 passages, we showed that the different clones must indeed have originated from different cells.