Molecular genetic characterization of both components of a dedifferentiated chondrosarcoma, with implications for its histogenesis

Dedifferentiated chondrosarcoma is defined as a high-grade, anaplastic sarcoma adjacent to a low-grade malignant cartilage-forming tumour. Controversy remains as to whether the anaplastic and cartilaginous components are derived from a common precursor cell, or whether they represent separate genotypic lineages (collision tumour). Both components of a case of dedifferentiated chondrosarcoma were therefore separately investigated by loss of heterozygosity (LOH) analysis, comparative genomic hybridization (CGH), DNA flow cytometry, and p53 analysis. Both showed p53 overexpression and an identical somatic 6 bp deletion in exon 7 of p53. Combination of the CGH and LOH results revealed that both components had lost the same copy of chromosome 13. These results provide compelling evidence in this case for a common origin, instead of the 'collision tumour' theory. Certain genotypic alterations were not shared. The anaplastic component showed severe aneuploidy, LOH at additional loci, and amplification and deletion of several chromosome parts. In contrast, the cartilaginous component had lost chromosomes 5, 22, 17p and part of 16p and revealed an amplification of 17q. The LOH and CGH results further demonstrated that the two components had lost a different copy of chromosome 4. Thus, a substantial number of genetic alterations have occurred after the diversion of the two components, indicating that the separation of the two clones, derived from a single precursor, was a relatively early event in the histogenesis of this case of dedifferentiated chondrosarcoma.

Presymptomatic testing for BRCA1 and BRCA2: how distressing are the pre-test weeks? Rotterdam/Leiden Genetics Working Group

Presymptomatic DNA testing for autosomal dominant hereditary breast/ovarian cancer (HBOC) became an option after the identification of the BRCA1 and BRCA2 genes in 1994-1995. Healthy female mutation carriers have a high lifetime risk for breast cancer (56-87%) or ovarian cancer (10-60%) and may opt for intensive breast and ovary surveillance or prophylactic surgery (mastectomy/oophorectomy). We studied general and cancer related distress in 85 healthy women with a 25% or 50% risk of being carrier of a BRCA1/BRCA2 gene mutation and 66 partners in the six to eight week period between genetic counselling/blood sampling and disclosure of the test result. Questionnaire and interview data are analysed. Associations are explored between levels of distress and (1) expected consequences of being identified as a mutation carrier, (2) personality traits, (3) sociodemographic variables, and (4) experiences related to HBOC. Mean pre-test anxiety and depression levels in women at risk of being a carrier and partners were similar to those of a normal Dutch population. In about 25% of those at risk of being a carrier and 10% of the partners, increased to high levels of general and cancer related distress were found. Increased levels of distress were reported by women who (1) anticipated an increase in problems after an unfavourable test outcome, (2) considered prophylactic mastectomy if found to be mutation carrier, (3) had an unoptimistic personality, (4) tended to suppress their emotions, (5) were younger than 40 years, and (6) were more familiar with the serious consequences of HBOC. Recently obtained awareness of the genetic nature of cancer in the family was not predictive of distress.The majority of the women and their partners experienced a relatively calm period before the disclosure of the test result and seemed to postpone distressing thoughts until the week of disclosure of the result. The low distress levels may partly be explained by the use of strategies to minimise the emotional impact of a possibly unfavourable test outcome. However, a minority reported feeling very distressed. Several factors were found to be predictive for increased distress levels.

Genetic alterations on chromosome 16 and 17 are important features of ductal carcinoma in situ of the breast and are associated with histologic type

We analysed the involvement of known and putative tumour suppressor- and oncogene loci in ductal carcinoma in situ (DCIS) by microsatellite analysis (LOH), Southern blotting and comparative genomic hybridization (CGH). A total of 78 pure DCIS cases, classified histologically as well, intermediately and poorly differentiated, were examined for LOH with 76 markers dispersed along all chromosome arms. LOH on chromosome 17 was more frequent in poorly differentiated DCIS (70%) Compared to well-differentiated DCIS (17%), whereas loss on chromosome 16 was associated with well- and intermediately differentiated DCIS (66%). For a subset we have done Southern blot-and CGH analysis. C-erbB2/neu was amplified in 30% of poorly differentiated DCIS. No amplification was found of c-myc, mdm2, bek, flg and the epidermal growth factor (EGF)-receptor. By CGH, most frequent alterations in poorly differentiated DCIS were gains on 8q and 17q22-24 and deletion on 17p, whereas in well-differentiated DCIS amplification on chromosome 1q and deletion on 16q were found. In conclusion, our data indicates that inactivation of a yet unknown tumour suppressor gene on chromosome 16q is implicated in the development of most well and intermediately differentiated DCIS whereas amplification and inactivation of various genes on chromosome 17 are implicated in the development of poorly differentiated DCIS. Furthermore these data show that there is a genetic basis for the classification of DCIS in a well and poorly differentiated type and support the evidence of different genetic routes to develop a specific type of carcinoma in situ of the breast.

Loss of heterozygosity and DNA ploidy point to a diverging genetic mechanism in the origin of peripheral and central chondrosarcoma

Chondrosarcomas are malignant cartilaginous tumors arising centrally in bone (central chondrosarcoma), or secondarily within the cartilaginous cap of a hereditary or sporadic exostosis (peripheral chondrosarcoma). Loss of heterozygosity (LOH) was studied by microsatellite analysis at the loci harboring the EXT genes (implicated in hereditary multiple exostoses), the EXT-like genes, and at 9p21, 13q14, 17p13, and chromosome 10. Nineteen of 20 peripheral chondrosarcomas showed LOH at all loci tested, while only 3 of 12 central chondrosarcomas exhibited LOH, restricted to 9p21, 10, 13q14, and 17p13. LOH at 9p21 did not appear to involve the CDKN2A gene, as assessed by SSCP analysis. DNA flow cytometry demonstrated a wide variation in the ploidy status in peripheral chondrosarcomas (DNA indexes, 0.56-2.01), whereas central chondrosarcomas were predominantly peridiploid. Near-haploidy found in peripheral chondrosarcomas could explain part of the high LOH percentages. Ki-67 immunohistochemistry suggested a higher proliferation rate in peripheral chondrosarcomas. Our results indicate that peripheral chondrosarcomas, arising secondarily to an exostosis, may obtain genetic alterations during malignant transformation, with subsequent genetic instability as demonstrated by a high percentage of LOH and a wide variation in ploidy status. In contrast, peridiploidy and a low percentage of LOH in central tumors suggest that a different oncogenic molecular mechanism may be operative.

Different profiles of allelic losses in cervical carcinoma cases in Surinam and The Netherlands

BACKGROUND

Cervical carcinoma is the second most common malignancy among women worldwide. The highest incidence rates are observed in developing countries. The increased susceptibility to cervical carcinoma in high incidence populations may result from several factors including human papillomavirus exposure and both inherited and acquired genetic traits. Using comparative molecular analysis of cervical carcinomas from Surinam, a high incidence area, and the Netherlands, a low incidence area, distinct molecular genetic profiles were studied in two populations with contrasting risk for the disease.

METHODS

In the two populations, the authors compared allelic loss as a marker for the involvement of putative tumor suppressor genes in 40 and 67 carcinoma specimens from Surinam and the Netherlands, respectively. Loss of heterozygosity (LOH) analysis was performed using polymorphic microsatellite markers at sites of known tumor suppressor genes (17p [p53], 13q [Rb, BRCA2], 16q [E-cadherin], and 17q [BRCA1]) and at chromosomes 3p, 6p, 6q, and 11q, which frequently are lost in cervical carcinoma.

RESULTS

Remarkable differences in LOH were found between both populations. The most prominent observation was the extremely high frequency of LOH, up to 72%, in the region of the major histocompatibility complex on chromosome 6p in specimens from Surinam. In the group of specimens from the Netherlands, only 45% of LOH was observed at this locus. In addition, LOH was detected significantly more frequently at 6q and 13q in the cases from Surinam whereas LOH was found more frequently at 17p in cases from the Netherlands.

CONCLUSIONS

The results of the current study show that heterogeneity exists in tumor-associated somatic genetic alterations between these two populations that may be indicative of the existence of multiple genetic pathways in cervical tumorigenesis.

EXT-mutation analysis and loss of heterozygosity in sporadic and hereditary osteochondromas and secondary chondrosarcomas

Osteochondromas occur as sporadic solitary lesions or as multiple lesions, characterizing the hereditary multiple exostoses syndrome (EXT). Approximately 15% of all chondrosarcomas arise within the cartilaginous cap of an osteochondroma. EXT is genetically heterogeneous, and two genes, EXT1 and EXT2, located on 8q24 and 11p11-p12, respectively, have been cloned. It is still unclear whether osteochondroma is a developmental disorder or a true neoplasm. Furthermore, it is unclear whether inactivation of both alleles of an EXT gene, according to the tumor-suppressor model, is required for osteochondroma development, or whether a single EXT germline mutation acts in a dominant negative way. We therefore studied loss of heterozygosity and DNA ploidy in eight sporadic and six hereditary osteochondromas. EXT1- and EXT2-mutation analysis was performed in a total of 34 sporadic and hereditary osteochondromas and secondary peripheral chondrosarcomas. We demonstrated osteochondroma to be a true neoplasm, since aneuploidy was found in 4 of 10 osteochondromas. Furthermore, LOH was almost exclusively found at the EXT1 locus in 5 of 14 osteochondromas. Four novel constitutional cDNA alterations were detected in exon 1 of EXT1. Two patients with multiple osteochondromas demonstrated a germline mutation combined with loss of the remaining wild-type allele in three osteochondromas, indicating that, in cartilaginous cells of the growth plate, inactivation of both copies of the EXT1 gene is required for osteochondroma formation in hereditary cases. In contrast, no somatic EXT1 cDNA alterations were found in sporadic osteochondromas. No mutations were found in the EXT2 gene.

Genomic structure of the human PLZF gene

The human PLZF (promyelocytic leukaemia zinc finger) gene encodes a Krüppel-like zinc finger protein, which was identified via the reciprocal translocation t(11;17)(q23;q21) fusing it to the retinoic acid receptor alpha (RARalpha) gene in promyelocytic leukaemia. To determine its complete genomic organisation, we constructed a cosmid-map fully containing the hPLZF gene. The gene has seven exons, including a novel 5' untranslated exon, varying in size from 87 to 1358bp and spans at least 120kb. Flanking intronic sequences were identified and all splice acceptor and donor sites conformed to the gt/ag rule. Five polymorphic markers could be fine located in its vicinity. These data will facilitate mutation analysis of hPLZF in t(11;17) leukaemia cases, as well as assist mapping and loss-of-heterozygosity analysis. Here we have tested hPLZF as a possible candidate for the PGL1 locus involved in hereditary head and neck paragangliomas. However, mutation analysis revealed no aberration in 12 paraganglioma patients from different families.

Repositioning the hereditary paraganglioma critical region on chromosome band 11q23

Hereditary paragangliomas (PGL, glomus tumors, MIM no.168000) are mostly benign, slow-growing tumors of the head and neck region. The gene (or genes) affecting risk to PGL are subject to genomic imprinting: children of affected fathers exhibit an autosomal dominant pattern of disease inheritance, whereas children of affected mothers rarely if ever develop the disease through maternal transmission. We previously confined the disease gene to an approximately 6 Mb critical region on chromosome band 11q23 (PGL1). Based on haplotype analysis of an extended Dutch pedigree, a 2 Mb sub-region between D11S938 and D11S1885 was proposed as the PGL1 critical interval. In this study, we excluded this interval by analysis of two new single tandem repeat polymorphisms (STRP) contained therein. Instead, we predicted a non-overlapping, more proximal 2 Mb critical interval between D11S1647 and D11S897, and evaluated this new region using nine STRP (D11S1986, five new, closely-linked STRP, D11S1347, D11S3178, and D11S1987). Consistent with our prediction, we observed substantial haplotype-sharing within the Dutch pedigree. We also analyzed four new American PGL families. A recombination event detected in one family further defined D11S1347 as the new telomeric border. We observed significant haplotype-sharing within this new interval among three unrelated American PGL families, strongly suggesting that they originated from a common ancestor. Thus, we confined PGL1 to an approximately 1.5 Mb region between D11S1986 and D11S1347, and showed identity-by-descent sharing for a group of American PGL families.

Mutation analysis of the Fanconi anaemia A gene in breast tumours with loss of heterozygosity at 16q24.3

The recently identified Fanconi anaemia A (FAA) gene is located on chromosomal band 16q24.3 within a region that has been frequently reported to show loss of heterozygosity (LOH) in breast cancer. FAA mutation analysis of 19 breast tumours with specific LOH at 16q24.3 was performed. Single-stranded conformational polymorphism (SSCP) analysis on cDNA and genomic DNA, and Southern blotting failed to identify any tumour-specific mutations. Five polymorphisms were identified, but frequencies of occurrence did not deviate from those in a normal control population. Therefore, the FAA gene is not the gene targeted by LOH at 16q24.3 in breast cancer. Another tumour suppressor gene in this chromosomal region remains to be identified.

Cyclin D1 gene amplification and overexpression are present in ductal carcinoma in situ of the breast

Cyclin D1 (CCND1) amplification is found in 10-15 per cent of invasive breast carcinomas, but it is not well established whether this gene alteration also occurs in the precursor of invasive breast carcinoma, ductal carcinoma in situ (DCIS). By Southern blot analysis, cyclin D1 gene amplification was detected in 10 per cent (3/32) of DCIS cases. In addition, 15 cases of DCIS were analysed using bright field in situ hybridization (BRISH), of which 11 had already been analysed by Southern blotting. One additional case with gene amplification was found by BRISH. The use of BRISH for the detection of gene amplification is shown to be a novel and reliable in situ method on paraffin-embedded tissue sections. By immunohistochemistry, 147 cases of DCIS were analysed for the expression of cyclin D1. Cyclin D1 overexpression was found in 9 per cent of well-differentiated, 29 per cent of intermediately differentiated, and 19 per cent of poorly differentiated DCIS. No statistically significant association was found between cyclin D1 overexpression and the differentiation grade of DCIS, although 90 per cent of the cases that show overexpression are classified as intermediately and poorly differentiated. An association was found between cyclin D1 overexpression and oestrogen receptor positivity. Cyclin D1 overexpression was found in all four cases with cyclin D1 gene amplification, but was also found in 30 per cent (8/27) of cases without detectable gene amplification. It is concluded that cyclin D1 gene amplification is an early event in the development of breast carcinoma and occurs in poorly differentiated DCIS. Cyclin D1 protein overexpression is also present in tumours without cyclin D1 gene amplification and is seen predominantly in DCIS of intermediately and poorly differentiated histological type and oestrogen receptor positivity.

Tissue chimerism in human cryopreserved homograft valve explants demonstrated by in situ hybridization

BACKGROUND

The presence of viable cells may contribute to increased homograft valve durability. These cells may be of infiltrating recipient or persisting donor origin. In this study, in situ hybridization was used to assess the origin of cells in cryopreserved homograft valve explants.

METHODS

A total of 10 homografts with a donor-recipient gender mismatch were acquired from patients whose graft had been explanted at reoperation or at autopsy. The period of implantation varied from 14 days to 70 months. Frozen sections were made and alternately examined with hematoxylin and eosin staining and in situ hybridization. Male cells were distinguished from female using a biotinylated Y-chromosome-specific deoxyribonucleic acid probe.

RESULTS

No endothelial cells were found. Thirty percent of the leaflets showed large acellular zones and 30% were completely acellular. The homograft arterial wall was occupied by a vast majority of penetrating host fibroblasts in 80% of the studied specimens. Donor and recipient cells were coexistent in the wall in 60% of the studied specimens and in 50% of the leaflets. In 30% only host cells could be identified.

CONCLUSIONS

This finding of tissue chimerism may lead to new insights in homograft pathology. The technique of in situ hybridization may provide an indispensable contribution in further homograft research.

Paragangliomas of the head and neck region show complete loss of heterozygosity at 11q22-q23 in chief cells and the flow-sorted DNA aneuploid fraction

Nonchromaffin paragangliomas of the head and neck region, also known as glomus tumors, are usually benign neoplasms consisting of clusters of chief cells surrounded by sustentacular cells arranged in so-called 'Zellballen.' Most of the patients have a familial background. In a previous study, examining all chromosome arms, we found loss of heterozygosity (LOH) predominantly at the chromosome 11q22-q23 region, where the disease causing gene PGL1 has been located by linkage analysis. However, all tumors showed only partial loss of allele signal intensities, and it was not clear whether this represented allelic imbalance or cellular heterogeneity. In the current study, we have performed LOH analysis for the 11q22-q23 region on DNA-aneuploid tumor cells, enriched by flow sorting, and on purified chief cell fractions obtained by single-cell microdissection. Complete LOH was found for two markers (D11S560 and CD3D) in the flow-sorted aneuploid fractions, whereas no LOH was found in the diploid fractions of three tumors. The microdissected chief cells from two of these tumors also showed complete LOH for both markers, indicating that the chief cells are clonal proliferated tumor cells. These results indicate that the PGL1 gene is likely to be a tumor suppressor gene, which is inactivated according to the two-hit model of Knudson. Furthermore, it shows that chief cells are a major if not the sole neoplastic component of paragangliomas.

Characterization and screening for mutations of the growth arrest-specific 11 (GAS11) and C16orf3 genes at 16q24.3 in breast cancer

Loss of heterozygosity involving the long arm of chromosome 16 is a frequent event seen in a number of human carcinomas, including breast, prostate, hepatocellular, and ovarian cancers. A region found to be commonly deleted in breast and prostate carcinomas is located at 16q24.3, which suggests the presence of a tumor suppressor gene that may be altered in these two malignancies. A detailed physical and transcription map of this region that includes the loci defining the smallest region of deletion has been constructed. This report describes the characterization of a transcript located in this region, the growth arrest-specific 11 (GAS11) gene, which was viewed as a potential tumor suppressor gene due to the expression of its mouse homolog specifically during growth arrest. The gene consists of 11 exons spanning approximately 25 kb. Northern blot analysis identified two ubiquitously expressed mRNAs of 3.4 and 1.8 kb produced by the use of alternative polyadenylation sites. Another gene, C16orf3 (chromosome 16 open reading frame 3), was found to lie within intron 2 of GAS11. This gene appears intronless, is transcribed in the orientation opposite to that of GAS11, and is expressed at low levels. These genes were examined for mutations in breast tumor DNA, and both were excluded as tumor suppressor genes involved in breast cancer.

Multifactorial analysis of differences between sporadic breast cancers and cancers involving BRCA1 and BRCA2 mutations

BACKGROUND

We have previously demonstrated that breast cancers associated with inherited BRCA1 and BRCA2 gene mutations differ from each other in their histopathologic appearances and that each of these types differs from breast cancers in patients unselected for family history (i.e., sporadic cancers). We have now conducted a more detailed examination of cytologic and architectural features of these tumors.

METHODS

Specimens of tumor tissue (5-microm-thick sections) were examined independently by two pathologists, who were unaware of the case or control subject status, for the presence of cell mitosis, lymphocytic infiltration, continuous pushing margins, and solid sheets of cancer cells; cell nuclei, cell nucleoli, cell necrosis, and cell borders were also evaluated. The resulting data were combined with previously available information on tumor type and tumor grade and further evaluated by multifactorial analysis. All statistical tests are two-sided.

RESULTS

Cancers associated with BRCA1 mutations exhibited higher mitotic counts (P = .001), a greater proportion of the tumor with a continuous pushing margin (P<.0001), and more lymphocytic infiltration (P = .002) than sporadic (i.e., control) cancers. Cancers associated with BRCA2 mutations exhibited a higher score for tubule formation (fewer tubules) (P = .0002), a higher proportion of the tumor perimeter with a continuous pushing margin (P<.0001), and a lower mitotic count (P = .003) than control cancers.

CONCLUSIONS

Our study has identified key features of the histologic phenotypes of breast cancers in carriers of mutant BRCA1 and BRCA2 genes. This information may improve the classification of breast cancers in individuals with a family history of the disease and may ultimately aid in the clinical management of patients.

Founder effect at PGL1 in hereditary head and neck paraganglioma families from the Netherlands

PGL1, a gene responsible for hereditary paragangliomas of the head and neck, recently was mapped to a 2-cM interval on chromosome 11q22-q23, by linkage and haplotype-sharing analysis of a large multibranch Dutch family. We determined the disease-linked haplotype, as defined by 13 markers encompassing a large interval on 11q21-q23, in 10 additional families ascertained from the same geographical locale. Alleles were identical for six contiguous markers, spanning a genetic distance of 6 cM and containing PGL1. Despite this strong indication of a common ancestor, no kinships between the families could be demonstrated through genealogical surveys going back to 1800 a.d. We conclude that a single ancestral mutation is responsible for most, if not all, hereditary paragangliomas, in this region of The Netherlands, and that strong founder effects may exist at the PGL1 locus.

Comparative genomic hybridization with lissamine- and fluorescein-labeled nucleotides

Biotin deoxyuridine 5'-triphosphate (dUTP) and digoxigenin dUTP are the labels most commonly used in comparative genomic hybridization (CGH). The relative infrequent use of direct fluorochrome-labeled nucleotides in CGH is related to the lower sensitivity they provide. Here we report the evaluation of two fluorochrome-conjugated nucleotides that have not been previously used in CGH (lissamine-5-dUTP and fluorescein-N6dATP) and show that this direct label combination performs at least as well as the indirect biotin/digoxigenin pair.

Micrometastases and survival in stage II colorectal cancer

BACKGROUND

Standard treatment of colorectal cancer includes adjuvant chemotherapy for patients with stage III disease (defined by the presence of lymph-node metastases), but not for patients with stage II tumors (who have no lymph-node metastases). However, 20 percent of patients with stage II tumors die of recurrent disease. We investigated whether the detection of micrometastases can be used to identify patients with stage II disease who are at high risk for recurrence.

METHODS

We analyzed 192 lymph nodes from 26 consecutive patients with stage II colorectal cancer, using a carcinoembryonic antigen-specific nested reverse-transcriptase polymerase chain reaction. Five-year follow-up information was obtained on all patients. Observed and adjusted survival rates were assessed in the patients with and the patients without micrometastases.

RESULTS

Micrometastases were detected in one or more lymph nodes from 14 of 26 patients (54 percent). The adjusted five-year survival rate (for which only cancer-related deaths were considered) was 50 percent in this group, whereas in the 12 patients without micrometastases, the survival rate was 91 percent (P=0.02 by the log-rank test). The observed five-year survival rates were 36 percent and 75 percent, respectively (P=0.03). The groups were similar with respect to age, sex, tumor side (location in relation to the flexura lienalis), degree of tumor differentiation (grade), and diameter of the primary tumor.

CONCLUSIONS

Molecular detection of micrometastases is a prognostic tool in stage II colorectal cancer.

Assessing genetic markers of tumour progression in the context of intratumour heterogeneity

This is a report from the Kananaskis working group on quantitative methods in tumour heterogeneity. Tumour progression is currently believed to result from genetic instability and consequent acquisition of new genetic properties in some of the tumour cells. Cross-sectional assessment of genetic markers for human tumours requires quantifiable measures of intratumour heterogeneity for each parameter or characteristic observed; the relevance of heterogeneity to tumour progression can best be ascertained by repeated assessment along a tumour progressional time line. This paper outlines experimental and analytic considerations that, with repeated use, should lead to a better understanding of tumour heterogeneity, and hence, to improvements in patient diagnosis and therapy. Four general principles were agreed upon at the Symposium: (1) the concept of heterogeneity requires a quantifiable definition so that it can be assessed repeatably; (2) the quantification of heterogeneity is necessary so that testable hypotheses may be formulated and checked to determine the degree of support from observed data; (3) it is necessary to consider (a) what is being measured, (b) what is currently measurable, and (c) what should be measured; and (4) the proposal of working models is a useful step that will assist our understanding of the origins and significance of heterogeneity in tumours. The properties of these models should then be studied so that hypotheses may be refined and validated.

Molecular genetic evidence for the conversion hypothesis of the origin of malignant mixed müllerian tumours

The origin of malignant mixed Müllerian tumours (MMMTs) has long been debated, due to the indefinite relationship between epithelial and mesenchymal malignant cells. In order to obtain insight into the clonal relationship between the two components of these tumours, molecular genetic changes were investigated at the level of loss of heterozygosity (LOH) in both cells types. LOH was studied in a series of six cases with 74 polymorphic microsatellite markers mapping to 19 different chromosomes. The epithelial and the mesenchymal neoplastic cells were separately microdissected from formalin-fixed, paraffin-embedded tissue, prior to DNA isolation. LOH was observed for 35 different markers mapping to chromosomes 3, 6, 8, 11, 15, 16, 17, 18, 21, and X. The most frequently involved chromosomes were 17p, 17q, 11q, 15q, and 21q. LOH was observed in five out of six cases and identical alleles were lost in the epithelial and in the mesenchymal cells. No genetic differences were observed between the two cell types for any of the informative markers. Immunohistochemistry (IHC) and TP53 mutation analysis revealed involvement of TP53 in all cases. Mutations were identified in five MMMTs. In four tumours, of which three had a missense mutation, strong nuclear staining for p53 was observed. In the remaining two cases, the mutation resulted in a stop codon, with no nuclear staining for p53 by IHC. The results support a monoclonal origin of MMMTs, with the absence of genetic changes uniquely associated with either of the phenotypes. The latter finding is compatible with current opinion that these neoplasms should be considered as metaplastic carcinomas and supports the conversion hypothesis.

Simultaneous loss of E-cadherin and catenins in invasive lobular breast cancer and lobular carcinoma in situ

Loss of expression of the intercellular adhesion molecule E-cadherin frequently occurs in invasive lobular breast carcinomas as a result of mutational inactivation. Expression patterns of E-cadherin and the molecules comprising the cytoplasmic complex of adherens junctions, alpha-, beta- and gamma-catenin, were studied in a series of 38 lobular breast carcinomas with known E-cadherin mutation status. The effect of loss of E-cadherin by mutational inactivation (or other mechanisms) on the expression of catenins was investigated. Complete loss of plasma membrane-associated E-cadherin expression was observed in 32 out of 38 invasive lobular carcinomas, for which in 21 cases a mutation was found in the extracellular domain of E-cadherin. In total, 15 frameshift mutations of small deletions or insertions, ranging from 1 to 41 bp, three non-sense mutations, and three splice mutations were identified. Mutations were scattered over the whole coding region and no hot spots could be detected. In all cases, simultaneous loss of E-cadherin and alpha- and beta-catenin expression was found; in 50 per cent of these cases, additional loss of gamma-catenin was observed. In six invasive lobular carcinomas, expression of both E-cadherin and catenins was retained. In none of these carcinomas was an E-cadherin mutation detected. Lobular carcinoma in situ adjacent to invasive lobular carcinoma showed simultaneous loss of E-cadherin and catenins in all the cases studied--remarkably, also, in four cases positive for E-cadherin and catenin expression in the invasive component. These results indicate that simultaneous loss of E-cadherin and alpha-, beta- and gamma-catenin may be an important step in the formation of lobular carcinoma in situ, as a precursor of invasive lobular breast cancer. Events additional to E-cadherin inactivation must be involved in the transition of lobular carcinoma in situ to invasive lobular carcinoma.

BRCA1 genomic deletions are major founder mutations in Dutch breast cancer patients

To date, more than 300 distinct small deletions, insertions and point mutations, mostly leading to premature termination of translation, have been reported in the breast/ovarian-cancer susceptibility gene BRCA1. The elevated frequencies of some mutations in certain ethnic subpopulations are caused by founder effects, rather than by mutation hotspots. Here we report that the currently available mutation spectrum of BRCA1 has been biased by PCR-based mutation-screening methods, such as SSCP, the protein truncation test (PTT) and direct sequencing, using genomic DNA as template. Three large genomic deletions that are not detected by these approaches comprise 36% of all BRCA1 mutations found in Dutch breast-cancer families to date. A 510-bp Alu-mediated deletion comprising exon 22 was found in 8 of 170 breast-cancer families recruited for research purposes and in 6 of 49 probands referred to the Amsterdam Family Cancer Clinic for genetic counselling. In addition, a 3,835-bp Alu-mediated deletion encompassing exon 13 was detected in 4 of 170 research families, while an deletion of approximately 14 kb was detected in a single family [corrected]. Haplotype analyses indicated that each recurrent deletion had a single common ancestor.

Facts in cancer genetics

During the past decade molecular biology and molecular genetics have greatly increased our understanding of the basic mechanisms in cancer development. The essential outcome of these molecular studies is that cancer can be considered as a genetic disease of cells. Both the non-hereditary (sporadic) cancers, as well as the hereditary forms of cancer are caused by genetic accidents that perturb the complex and delicate cellular growth control systems. Thus, at the molecular level, no principal difference exists between hereditary- and non-hereditary forms of cancer and it can be stated that both at the level of the single cell as well at the level of the individual, cancer is a genetic disease. Whereas in hereditary cancer, the risk gene is passed through the germline to the next generation, in sporadic cancer, a cancer cells passes its abnormal genes to its daughter cells at cell division. It is therefore not surprising that one of the main priorities in cancer research today is the identification of the culprit genes and characterizing the function of their normal products. Genes associated with hereditary cancer syndromes essentially encompass two classes of genes viz. tumor suppressor genes and genes controlling genomic stability (DNA-mismatch repair genes). Although germline mutations in these susceptibility genes are associated with significantly increased cancer risk, even up to 90%, additional genetic factors and interaction with environmental factors eventually determine if a carrier of a germline mutation will develop cancer.

Identification of host and donor cells in porcine homograft heart valve explants by fluorescence in situ hybridization

The pathogenesis of the primary tissue degeneration that limits the life-span of aortic and pulmonary homografts has still not been revealed. Histopathological studies on homograft explants have not given definitive insight into the eventual fate of donor cells, nor have they demonstrated the assumed importance of host cell ingrowth into the graft tissue. In this experimental study, fluorescence in situ hybridization (FISH) is introduced as a new approach to examine the distribution of host and donor cells in homograft explants. Aortic valve replacement was performed with a cryopreserved porcine aortic homograft in three pigs; donor and recipient were of opposite sex. After 4 months, the grafts were explanted and examined by FISH using a biotinylated porcine Y-chromosome-specific library probe. Following probe detection with FITC-conjugated avidin, a clear distinction could be made between cells of host and donor origin without distorting the histological integrity of the explants. There was ingrowth of donor cells into the graft aortic wall and into the valve leaflet, to some extent. In all explants, remaining donor cells were present, though decreased in number. The introduction of FISH in homograft heart valve research provides a powerful tool to study the fate of recipient and donor cellular elements in situ, and may therefore contribute to a better understanding of the histopathological processes that take place in transplanted homograft valves.