Recessive mechanisms of malignancy

A rationalized definition of general tumor suppressor microRNAs excludes miR-34a

While several microRNAs (miRNAs) have been proposed to act as tumor suppressors, a consensual definition of tumor suppressing miRNAs is still missing. Similarly to coding genes, we propose that tumor suppressor miRNAs must show evidence of genetic or epigenetic inactivation in cancers, and exhibit an anti-tumorigenic (e.g., anti-proliferative) activity under endogenous expression levels. Here we observe that this definition excludes the most extensively studied tumor suppressor candidate miRNA, miR-34a. In analyzable cancer types, miR-34a does not appear to be down-regulated in primary tumors relatively to normal adjacent tissues. Deletion of miR-34a is occasionally found in human cancers, but it does not seem to be driven by an anti-tumorigenic activity of the miRNA, since it is not observed upon smaller, miR-34a-specific alterations. Its anti-proliferative action was observed upon large, supra-physiological transfection of synthetic miR-34a in cultured cells, and our data indicates that endogenous miR-34a levels do not have such an effect. Our results therefore argue against a general tumor suppressive function for miR-34a, providing an explanation to the lack of efficiency of synthetic miR-34a administration against solid tumors.

Genomic Alterations in Human Breast Cancer: A Review

We review and discuss data on the genetic alterations documented in human breast carcinomas at the molecular level. These alterations may result in: 1) deletion of genetic material (chromosome 11p, 13q, 3p, 1q, 17p); 2) amplification of genes or entire chromosomal segments (c-myc, c-erb-B2, locus DF3/PUM, loci on 11q13); 3) rearrangements (c-myc); 4) point mutations (c-ras). Presently available informations do not allow the development of cohesive pathogenetic models but indicate that the molecular basis of human breast cancer is heterogeneous.

Genetic alterations on chromosome 17 in human breast cancer: relationships to clinical features and DNA ploidy

We analyzed DNA from 105 primary breast cancers to assess amplification of the ERBB2 gene and loss of heterozygosity (LOH) on chromosome 17 using 4 polymorphic markers, and investigated the relationships of these genetic alterations to clinicopathological characteristics including DNA ploidy. Amplification of the ERBB2 gene was observed in 28% of the tumors. ERBB2 was amplified in tumors of all clinical stages and amplification was significantly linked to lymph node metastasis. LOH at D17S5 was observed in 28 of 57 informative tumors, while 17 of 62 informative tumors showed allelic loss at TP53. Among the 37 tumors informative for both loci, 32% showed LOH at these loci and 49% retained both alleles, indicating that there was a significant relationship between LOH at D17S5 and at TP53. We also examined LOH at the D17S74 and NME1 loci on chromosome 17q. LOH at D17S74 and NME1 was observed in 20% and 22% of the informative tumors, respectively, but there was no significant association between LOH at these loci. Of the 4 loci tested, LOH at TP53, D17S74, and NME1 was associated with clinical stage. Lymph node metastasis was correlated with LOH at NME1. Moreover, allelic loss was more frequent in aneuploid tumors than in diploid tumors. These results suggest that certain combinations of genetic alterations on chromosome 17 may cooperate in the development and/or progression of breast cancer. Furthermore, it seems likely that analysis of these alterations in breast cancer patients may provide useful prognostic information.

Loss of constitutional heterozygosity on chromosome 11p in human ovarian cancer. Positive correlation with grade of differentiation

BACKGROUND

There is increasing evidence suggesting that genes located on the short arm of chromosome 11 play an important role in the development of human ovarian cancer. Recent cytogenetic and molecular studies have demonstrated the loss of genetic material in this region. Loss of normal growth regulatory genes may allow for the expression of tumorigenicity or lead to tumor progression.

METHODS

The authors used DNA recombinant techniques to examine the frequency of allelic losses at four loci spanning the chromosomal region 11p15.1-11p15.5 in 40 patients with malignant ovarian tumors. DNA extracts from normal leukocytes and 48 tumor samples were analyzed by Southern blotting using the polymorphic probes pEJ6.6 (HRAS1), phins310 (INS), p20.36 (PTH), and pEM36 (CALCA).

RESULTS

Reduction to homozygosity in the tumor DNA was found in 47.5% of the informative cases (19 of 40). Comparing the results with clinical parameters, none of the well-differentiated tumors (6 of 40, Grade 1) and only one of the early stage tumors (6 of 40, International Federation of Gynecology and Obstetrics [FIGO] Stage I or II) showed alterations in this chromosome region. Statistical analysis revealed a strong correlation of rate of loss of constitutional heterozygosity (LOH) and grade of differentiation, in the sense of higher 11p allele losses occurring in poorly differentiated tumors.

CONCLUSIONS

The authors concluded that the relatively high incidence of 11p allele losses marks an important step in ovarian cancer development. Furthermore, statistical analysis showed that loss of 11p alleles was strongly correlated with poorly differentiated ovarian cancer, indicating the location of genes involved in cellular functions associated with the development of more anaplastic tumors.

Congenital abnormalities in children with cancer and their relatives: results from a case-control study (IRESCC)

Several studies have revealed an excess of malformations in children with certain malignancies. A few environmental causes have been identified which may damage the foetus and lead to malformation and cancer. However, most of the numerous recognised cancer/malformation syndromes are genetically determined. This report describes a case-control study of 555 newly diagnosed children with cancer and 1,110 matched controls, chosen from general practitioner lists (GP controls) and hospital admissions (H controls). Their parents were interviewed on topics of possible aetiological significance and medical records were checked to confirm reports at interview. The numbers of congenital malformations in the index and GP control children, and the relatives of the index children, the GP and H controls are described. There were more children with malformations among the cases (60/555) than among the GP controls (27/555), P < 0.001. The abnormalities in the cases included eight with specific chromosomal/genetic conditions (e.g. Down's syndrome, XY gonadal dysgenesis, Von Recklinghausen's neurofibromatosis, Goldenhar's syndrome) whereas only one GP control child had a chromosomal defect (P < 0.05). Five case children but no GP controls had neural tube defects; this is not statistically significant. No excess of malformations was found in the siblings of cases compared with GP and H control siblings. Case mothers had a small excess of malformations (22/555) compared with GP controls (8/555), P < 0.05. Among more distant relatives the results were difficult to interpret because of the relatively small numbers in the diagnostic subgroups and because of apparent under reporting in grandparents, but no striking differences were seen between case and control relatives. The excess of malformations found in children with cancer, compared with controls, without a similar excess of malformations in their close relatives may indicate that in some (perhaps very roughly one in 20) cases antenatal events may lead both to the malformation and the malignancy.

Genetic alterations in a malignant schwannoma from a patient with neurofibromatosis (NF1)

In a patient with neurofibromatosis (von Recklinghausen disease; NF1), normal lymphocytes, five cutaneous neurofibromas, and tumour tissue from a recurrence of a malignant schwannoma were analysed for genetic alterations. Eleven DNA markers located on chromosome 17 and nine randomly chosen markers representing chromosomes 1, 2, 3, 4, 5, 6, and 11, were analysed. High resolution Giemsa banding of lymphocytes revealed no chromosomal rearrangement. The DNA from the neurofibromas were all found to have the same restricted fragment length polymorphism pattern as the constitutional DNA from the patient. In the malignant schwannoma a complete loss of one allele was found at polymorphic loci on chromosome arm 17p. One gene copy of the TP53 gene (17p13.1) and the NF1 gene (17q11.2) was lost, as was one copy of the PGA gene (11q13). No mutations were detected in the mutational hotspots of the TP53 gene. Partial losses were detected at three loci on chromosomes 1, 2 and 6, indicating a clonal variation within the tumour since histological evaluation disclosed no normal tissue in the analysed specimen. Our data indicate that the NF1 gene may function as a tumour suppressor gene, and that, either by effect of dose reduction or complete inactivation, both the NF1 gene and the TP53 gene may be critical for the progression of a neurofibroma to a malignant schwannoma. The observations made are consistent with the concept of stepwise multigenetic changes in tumour progression.

Multiple polyps of esophagus, stomach, colon, and rectum accompanying rectal cancer in a patient with constitutional chromosomal inversion

BACKGROUND

It has been reported that colorectal carcinomas are caused by a multistage process. In patients with familial adenomatous polyposis, carcinoma of the colorectum frequently develops and occasionally polyps develop in the upper gastrointestinal tract. Chromosomal deletion often is found for chromosomes 5, 17, and 18, on which tumor suppressor genes are located. Furthermore, loss of the alleles of loci on chromosome 3 has been reported in renal cell carcinoma, small cell lung carcinoma, and mixed salivary gland tumor in hereditary and sporadic cases. These data support the concept of a recessive mechanism for the development of human tumors.

PATIENTS AND RESULTS

The authors report the case of a 48-year-old woman with rectal cancer accompanied by multiple polyps in the esophagus, stomach, and colorectum. Histologically, the polypoid lesions in the esophagus, stomach, and colorectum showed a thickened mucosa, hyperplastic polyps, and mixed hyperplastic adenomatous polyps, respectively. Karyotype analysis showed 46, xx, inv(3)(p12.2q25.3) in all 20 inspected peripheral lymphocytes. By Southern blot with a c-raf probe, one allele of the c-raf-1 gene, which has been mapped on chromosome 3p25, was deleted from the rearranged chromosome 3 in the peripheral lymphocytes, intact colonic mucosa, and cancer tissue.

CONCLUSIONS

These results suggest that the development of hyperplastic polyps and carcinoma of the rectum results from the allelic loss in chromosome 3p, as has been reported for solid tumors at other sites.

Sensitivity analysis of a new model of carcinogenesis

A new simulation model of carcinogenesis is described which, in addition to the features of a standard clonal two-stage model (loss of both copies of a tumor suppressor gene by point mutations, cell division and cell death), includes a quantitative description of mitotic recombination, DNA repair, and cell to cell interactions in all stages. The model is implemented as a discrete event process. The results of a sensitivity analysis of the model are presented. The most sensitive parameters were found to be: the number of normal cells at risk, and the division rate, death rate and DNA repair efficiency for the intermediate stage cells. Accurate information about these parameters is important for a quantitative understanding of carcinogenesis. The sensitivity of the model to the number of normal cells indicates the importance of understanding the nature of the cells at risk, for example, stem cells vs. differentiated cells. The model can be used to assess the importance of chromosomal damage such as mitotic recombination and epigenetic mechanisms such as hyperplasia and cytotoxicity in the onset of malignant tumors.

Familial versus sporadic breast cancer

BACKGROUND

Studies comparing patients with familial and sporadic breast cancer have indicated that a family history of the disease can increase a woman's risk for having the disease twofold to threefold and that patients with familial breast cancer have a younger age at diagnosis and have a higher frequency of bilateral disease than those with sporadic breast cancer. Also, at least four types of breast cancers have been shown to be inherited. These findings led to the hypothesis that familial and sporadic breast cancer are the consequence of two biologically distinct mechanisms.

METHODS

A two-step mutation model proposed by Knudson in 1971 provides a link between the molecular mechanisms underlying familial and sporadic breast cancer. According to this model, both cancers involve the same genomic change in homologous chromosomes. The only difference is that the first mutation is inherited and the second is somatic in familial cancer, whereas in sporadic cancer both mutations are somatic. Mutation is used in a broad sense and refers to either a point mutation at a specific locus or the loss of a locus by deletion or nondysfunction.

RESULTS

This model has been shown to apply to several childhood and adult cancers, including breast cancer. Based on this model, patients with familial breast cancer will have their disease earlier in life and will have more bilateral cancer than patients with sporadic breast cancer. Moreover, the two types of patients should show no differences in clinicopathologic characteristics because both types involve the same genomic change and the pathogenesis of both types should be the same, thus arguing against the early hypothesis that patients with familial and sporadic breast cancer are the consequence of biologically distinct mechanisms.

CONCLUSIONS

Breast cancer appears to involve the cumulative effect of several genetic lesions involving the activation of oncogenes and the inactivation of tumor-suppressor genes. Which genes are involved specifically as causative factors of breast cancer (the inherited gene or genes) and which are important somatically in its continued development and progression (oncogenes and tumor-suppressor genes) requires additional study.

Cytogenetic analysis of an adenoid cystic carcinoma of the Bartholin's gland. A rare, semimalignant tumor of the female genitourinary tract

Cytogenetic analysis has been performed on short-term cultures from a 56-year-old woman suffering from an adenoid cystic carcinoma of Bartholin's gland. Beside a normal female karyotype, the tumor revealed an abnormal cell line with complex chromosome changes involving the chromosomes 1, 4, 6, 11, 22, and 14. The mainly structural and nonbalanced rearrangements led to the loss of the chromosome segments 1p31----qter, 4q22----q28, 6p12----qter, 11p11.2----pter, 14q24----qter, and 22q13----qter. Clonal numerical aberrations were not observed. To our knowledge, such a tumor has to-date not been cytogenetically investigated.

Genetic alterations of the tumour suppressor gene regions 3p, 11p, 13q, 17p, and 17q in human breast carcinomas

Fifty-nine primary breast carcinomas and 11 metastases were examined to identify genetic alterations in the tumour suppressor gene regions 3p, 11p, 13q, 17p, and 17q. Loss of heterozygosity (LOH) was frequently observed on chromosome arms 17p (p144D6 lost in 75%, pYNZ22.1 in 55%, and TP53 in 48% of the primary tumours), 13q (RBI lost in 40% of the primary tumours), and 17q (pRMU3 lost in 35%, pTHH59 in 29%, and NM23HI in 26% of the primary tumours). Loss of all the markers except p144D6 was observed even more frequently in the metastases. Pairwise comparisons for concordance of allele losses on 17p indicated that there might be two genes on 17p implicated in breast cancer development; the TP53 gene and a gene located close to the p144D6 and pYNZ22.1 markers. LOH of the RBI gene was associated with LOH of pYNZ22.1 and p144D6, but not with LOH of TP53. LOH of RBI and TP53 was associated with occurrence of ductal carcinomas, RBI and p144D6 losses with tumour size, and p144D6 losses with positive node status as well. LOH of TP53 and the three 17q markers NM23HI, pTHH59, and pRMU3 was most frequently observed in tumours from postmenopausal women. p144D6 losses occurred most frequently in progesterone receptor-negative tumours, whereas pTHH59 losses occurred most frequently in oestrogen receptor-negative tumours. LOH of the investigated loci was not associated with ERBB2 protooncogene amplification, with positive family history of breast cancer, or with survival.

Chromosome rearrangements at 12q13 in two cases of chondrosarcomas

We analyzed the karyotypes of two moderately differentiated (grade 2) chondrosarcomas. Case 1 had a reciprocal translocation between chromosomes 6 and 12, t(6;12)(q25;q13) in most of the cells analyzed, as well as trisomies of chromosomes 7, 8, 11, 17, 19, and 21 and tetrasomy of chromosome 19. A reciprocal translocation involving chromosomes 12 and 19, t(12;19)(q13;q13), was noted as a highly clonal abnormality in the other case. Some cells had t(12;19) as the sole chromosome abnormality. Thus, chromosome rearrangements involving the long arm of chromosome 12 at the same region (q13) were commonly identified in the two tumors. These findings suggest that the rearrangements at 12q13 are nonrandom acquired changes that characterize a subgroup of chondrosarcomas.

Overexpression of the p53 protein and allele loss at 17p13 in ovarian carcinoma

Mouse monoclonal antibodies PAb 240 and PAb 1801 which specifically immunoprecipitate p53 protein, were used to examine 27 fresh ovarian tumours (16 serous adenocarcinomas, six endometrioid carcinomas, one mucinous adenocarcinoma, one mucinous borderline tumour and three benign adenomas). Eleven out of 16 (69%) serous adenocarcinomas and one endometrioid tumour showed positive staining with one or both antibodies and none of the mucinous or benign tumours stained with either antibody. DNA from tumour and peripheral blood leukocytes was used to identify allelic deletions on chromosome 17p in tumours. 11/12 positively staining tumours showed less of heterozygosity (LOH) on 17p at the nearest informative locus to the p53 gene. In this series of ovarian tumours, LOH on 17p correlates closely with the aberrant expression of the p53 protein in a high proportion of advanced stage serous adenocarcinomas. This observation suggests that the p53 tumour suppressor gene is involved in the evolution of epithelial ovarian cancer (EOC) and may have prognostic significance.

Cytogenetic and flow cytometric analysis of a clear cell chondrosarcoma

Cytogenetic analysis of a rare tumor, a clear cell chondrosarcoma of the spine, showed unusual karyotypic findings. The tumor had a predominant clone with a near-haploid chromosome complement of 30 chromosomes with loss of one homologue of each chromosome pair except chromosomes 5, 7, 12, and 19-22. A second clone with 58-60 chromosomes appeared to have originated by a doubling of the near-haploid clone. No structural changes were present. Comparison with other solid tumors and leukemias with near-haploid chromosome complements showed an interesting difference in the chromosomes which were preferentially disomic or monosomic in the two groups. Quantitative DNA analysis also showed aneuploid clones of cells corresponding to the near-haploid and hyperdiploid chromosome counts obtained cytogenetically.

Molecular genetics of human bladder carcinomas

Bladder cancer corresponds to a tumor type whose clinical behavior is difficult to predict. A better understanding of this pathology is expected from molecular genetics, which brings together cytogenetics and molecular biology. Therefore, we have tried to overview correlations between chromosome abnormalities and the presence, in the vicinity of the altered loci, of genes (oncogenes and others) that could be involved in bladder oncogenesis and/or tumor progression. In addition to oncogene activation by point mutations, gene amplification, or deregulation of gene expression, several cytogenetic as well as molecular evidences point to genetic deletions (existence of "tumor suppressor genes") being involved in those processes.

Alterations of oncogenes in metastatic tumours of human gastric carcinomas

To determine whether alterations in oncogenes are associated with tumour progression and metastasis, DNAs from 32 metastatic tumour samples of different sites in 12 autopsy cases of gastric carcinomas were analysed for alterations of ERBB, ERBB2, HST1, INT2 and LMYC genes by Southern blot hybridisation. DNAs from 89 primary gastric carcinomas including 69 advanced carcinomas and 20 early carcinomas were also examined. In primary tumours, no amplification was detected in early carcinomas, while amplification of ERBB and ERBB2 genes was detected in one (1.4%) and four (5.8%) out of 69 advanced carcinomas, respectively. In metastatic tumours, amplification of ERBB gene was detected in three metastatic tumours (9.4%), and all of them had allelic deletion of the LMYC gene. Regardless of histological type, amplification of ERBB2 gene was detected in 8 metastatic tumours (25.0%), out of which three tumours had coamplification of HST1 and INT2 genes. The incidence of ERBB2 amplification in metastatic tumours was significantly higher than that in primary tumours. These results indicate that multi-alterations in oncogenes might occur during tumour progression and metastasis of human gastric carcinomas.

Chromosomal rearrangements in a primary hepatocellular carcinoma

Chromosome analysis of cells obtained at biopsy from a 65-year-old man with primary hepatocellular carcinoma revealed characteristic abnormalities of chromosomes 1, 5, 6, 9, 13, 16, and 22 in each cell and maintenance of a pseudodiploid chromosome number (46,XY). Five of the chromosomal sites involved in these rearrangements are either in fragile site regions or in regions containing genes that encode cellular oncogenes. Some of the tumor cells manifest mitotic deviations in the form of asynchronies, spiralization, premature centromere division, and non-sister chromatid associations. The significance of these findings to hepatocellular carcinogenesis is discussed.

No evidence for loss of alleles at 11p in HBV negative hepatocellular carcinomas

The aim of the present study was to determine whether loss of DNA sequences at the chromosome arm 11p, where presumed tumor suppressor genes are located, might occur in hepatocellular carcinomas (HCCs) of hepatitis B virus (HBV) negative patients. Normal liver and HCC genotypes were compared at 6 loci on 11p with 7 polymorphic probes detecting 10 restriction length polymorphisms (RFLPs). Each of the 8 paired normal-tumor tissue samples was informative for at least three different loci on 11p13-pter. None of them showed loss of constitutional heterozygosity for those markers. The retainment of 11p alleles suggests that mechanisms other than loss of tumor suppressor genes on llp are involved in hepatocarcinogenesis of HBV negative patients.

Cytogenetic abnormalities in cancer: with special emphasis on tumor heterogeneity

There is a considerable amount of cytogenetic data available to support the statements that (1) cancer is a genetic disease; (2) most cancers are monoclonal in origin; (3) tumor cells are more genetically unstable than normal cells; (4) the genetic instability may be inherited, acquired, or both during the lifespan of the individual tumor; (5) tumor metastasis is a nonrandom, controlled process, and clonal in origin; (6) malignant tumors are genetically heterogeneous and contain multiple subpopulations that may differ in their biological properties; (7) some tumors might be difficult to treat successfully because of their resistant nature; and (8) tumor cells may acquire resistance because of gene amplification. For these reasons it is extremely important to study the biology of malignant tumor cells in order to determine their effective treatments and control this dreadful disease.

Developmental consequences of imprinting of parental chromosomes by DNA methylation

Genomic imprinting by epigenetic modifications, such as DNA methylation, confers functional differences on parental chromosomes during development so that neither the male nor the female genome is by itself totipotential. We propose that maternal chromosomes are needed at the time when embryonic cells are totipotential or pluripotential, but paternal chromosomes are probably required for the proliferation of progenitor cells of differentiated tissues. Selective elimination or proliferation of embryonic cells may occur if there is an imbalance in the parental origin of some alleles. The inheritance of repressed and derepressed chromatin structures probably constitutes the initial germ-line-dependent 'imprints'. The subsequent modifications, such as changes in DNA methylation during early development, will be affected by the initial inheritance of epigenetic modifications and by the genotype-specific modifier genes. A significant number of transgene inserts are prone to reversible methylation imprinting so that paternally transmitted transgenes are undermethylated, whereas maternal transmission results in hypermethylation. Hence, allelic differences in epigenetic modifications can affect their potential for expression. The germ line evidently reverses the previously acquired epigenetic modifications before the introduction of new modifications. Errors in the reversal process could result in the transmission of epigenetic modifications to subsequent generation(s) with consequent cumulative phenotypic and grandparental effects.

Chromosomal rearrangements in chondromatous tumors

Short-term cultures from 16 chondromatous tumors, 15 primary and one recurrent, were analyzed cytogenetically. Clonal chromosome aberrations were found in one of six benign tumors and in seven of ten malignant tumors. A chondroma had a complex translocation involving chromosomes X, 8, 12, and 13, as well as a deletion of the derivative chromosome 8. In the malignant tumors, monosomy 6 and 22 were observed in three tumors and monosomy 10, 11, 13, and 18 were observed in two tumors. In two of the three metastasizing tumors, del(5) (q13) and loss of chromosomes 6, 10, 11, 13, and 22 were common features. Structural aberrations of chromosome 1 were found in five tumors, of chromosomes 6, 12, and 15 in three tumors, and of chromosomes 4, 5, 9, and 20 in two tumors. We conclude that although considerable cytogenetic heterogeneity exists among chondromatous tumors, the karyotypic anomalies are still nonrandom.

Analysis of somatic cell hybrids derived from normal human prostatic epithelial cells fused with HeLa cells

Somatic cell hybrids have been instrumental in the recognition of specific chromosomes containing genes capable of suppressing the malignant phenotype. As a first step towards the identification of possible suppressor genes in prostate cells, we created hybrids by fusing normal prostate cells with malignant HeLa cells. Similar to hybrids made with other combinations of normal and malignant cells, the normal phenotype was dominant and the malignant phenotype was suppressed. The phenotype of the nontumorigenic hybrids after injection into nude mice resembled that of normal keratinocyte X HeLa hybrids, and tiny, nonprogressive keratinized nodules were produced. One hybrid clone was tumorigenic, possible due to the loss of a normal suppressor gene, and displayed glandular as well as squamous elements. Further characterization of these hybrids should permit isolation of specific suppressor genes, as well as promote recognition of elements that regulate the glandular phenotype.

Neuroblastoma consensus deletion maps to 1p36.1-2

At least 70% of human neuroblastomas display cytogenetically visible aberrations in the short arm of chromosome 1. We have used a panel of probes detecting polymorphic DNA loci, most of which were derived from a library of microdissected distal 1p chromosome fragments, to compare the hybridization pattern of DNA on nine different tumors and the corresponding normal tissue. In eight of the neuroblastomas allelic loss was observed with at least two probes. The deletions were of different size. Since a consensus deletion in all eight tumors included the segment 1p36.1-2, we conclude that genetic information related to neuroblastoma tumorigenesis is located within this approximately 10 megabase segment. Previous studies have revealed the amplification of MYCN in neuroblastomas. Our study did not provide evidence for a correlation between MYCN amplification and the 1p deletion, suggesting that the two genetic alterations result from molecular mechanisms that are not directly related to each other.

At least four different chromosomal regions are involved in loss of heterozygosity in human breast carcinoma

Three chromosome regions, i.e., 11p15, 13q, and 17p, were previously reported by three independent groups to be specifically reduced to hemizygosity in human primary breast cancer. We examined the DNA of 64 mammary tumors for loss of heterozygosity (LOH) with 28 polymorphic DNA markers dispersed on 10 arms of 8 different chromosomes. Complete or near-complete absence of LOH was observed on 5 arms (5 chromosomes). LOH at all three previously invoked regions was confirmed, and the highest frequency was found on 17p (67% of heterozygous patients). Allele loss of a marker from chromosome 3 (region p14-p21) was found in 7 of 15 informative cases. Concurrent LOH at 2 to 4 loci was noted in 20 of the 43 tumors showing LOH. Allele losses did not correlate with any of the six clinico-histopathological variables investigated, but in a group of patients in which we were unable to demonstrate LOH, the absence of distant metastases was statistically significant (P less than 0.05). These results suggest that some of the observed allele losses reflect random events, possibly as a result of genetic instability, but are not without biological significance for the progression of particular subclasses of breast tumors.

Homozygosity for 8pter----q22 in acute myeloblastic leukemia with t(8;21)(q22;q22)

A case of acute nonlymphocytic leukemia with homozygosity for the chromosome segment 8pter----8q22 is reported. A t(8;21)(q22;q22) translocation was associated with duplication of the derivative chromosome 8q- and absence of the normal chromosome 8. These rearrangements also yielded hemizygosity for 8q22----qter. This case shows that acquired hemizygosity and homozygosity do exist in leukemia as in solid malignant tumors.

Characteristic karyotypic anomalies identify subtypes of malignant fibrous histiocytoma

Cytogenetic analysis of short-term cultures from 25 malignant fibrous histiocytomas (MFH) revealed clonal chromosome abnormalities in 17 tumors: ten storiform-pleomorphic and seven myxoid MFH. Telomeric associations, rings, and dicentric chromosomes were present in 11 tumors and cytogenetic signs of gene amplification (homogeneously staining regions and double minute chromosomes) in four. The breakpoint distribution of the numerous structural rearrangements was nonrandom. The chromosome bands most frequently affected were 19p13 (in eight tumors; eight rearrangements gave rise to 19p+ markers, some of which looked similar, and an r(19) was found in one case), 11p11 (in seven tumors; three translocations and four deletions), 1q11 (in seven tumors; one translocation and six deletions), and 3p12 (in six tumors; all deletions). Other bands involved at least four times were 1p36, 5p15, and 20q13. Of particular clinical interest was the observation that tumors with 19p+ seemed to have a pronounced tendency to recur locally (local recurrence in five of eight tumors with 19p+ compared to one of nine in tumors without this aberration; observation period 4-16 months).

Mutator phenotype of Werner syndrome is characterized by extensive deletions

Werner syndrome (WS) is a rare autosomal-recessive disorder characterized by the premature appearance of features of normal aging in young adults. The extensive phenotypic overlap between WS and normal aging suggests they may also share pathogenetic mechanisms. We reported previously that somatic cells from WS patients demonstrate a propensity to develop chromosomal aberrations, including translocations, inversions, and deletions, and that WS cell lines demonstrate a high spontaneous mutation rate to 6-thioguanine resistance. We report here the biochemical and molecular characterization of spontaneous mutations at the X chromosome-linked hypoxanthine phosphoribosyltransferase (HPRT) locus in 6-thioguanine-resistant WS and control cells. Blot hybridization analysis of 89 independent spontaneous HPRT mutations in WS and control mutants lacking HPRT activity revealed an unusually high proportion of HPRT deletions in WS as compared with control cells (76% vs. 39%). Approximately half (58%) of the deletions in WS cells consisted of the loss of greater than 20 kilobases of DNA from the HPRT gene. These results suggest that an elevated somatic mutation rate, and particularly deletions, may play pathogenetically important roles in WS and in several associated age-dependent human disease processes.

Preferential mutation of paternally derived RB gene as the initial event in sporadic osteosarcoma

Successive loss of function of both alleles of the retinoblastoma susceptibility gene (RB) on human chromosome 13 seems to be critical in the development of retinoblastoma and osteosarcoma. In cases where the tumour is familial and susceptibility is inherited, a mutation in one of the alleles is carried in the germline. We have recently shown that cytogenetically visible germline mutations are usually in the paternally derived gene. Such a bias would not be expected for sporadic (non-familial) tumours, where both mutations occur in somatic tissue, but there has been some indication of a bias towards initial somatic mutation in the paternally derived gene on chromosome 11 in sporadic Wilms tumour. We have now examined 13 sporadic osteosarcomas and find evidence which indicates that in 12 cases the initial mutation was in the paternal gene, suggesting the involvement of germinal imprinting in producing the differential susceptibility of the two genes to mutation.

Adenocarcinoma and carcinoid developing spontaneously in the stomach of mutant strains of Mastomys natalensis

Neoplastic and nonneoplastic lesions developing spontaneously in antral and fundic mucosae of stomachs of mutant chamois-coloured Z (130 animals) and Y (67 animals) strains of Mastomys aged 18 to 24 months were examined histologically and histochemically. The Z strain developed both antral lesions (hyperplasia 29.2%; dysplasia 23.8%; adenocarcinoma 17.7%) and fundic carcinoid(s) (72.3%). The antral lesions were limited to the lesser curvature near the pyloric ring. Macroscopically, adenocarcinomas resembled human gastric carcinomas of either Borrmann's type I or II. Histochemically, adenocarcinoma cells were characterised by marked reduction of total mucins produced and predominance of mucins with both periodic acid-Schiff and Alcian blue reactivities (neutral and sialated class II mucins). An infiltrating adenocarcinoma was successfully transplanted into nude mice, reaching the 7th generation of transplantations over 4 years, and retained histological features of the primary tumour. The ultrastructural appearance of growing transplanted tumours supported the reduced production of mucins by adenocarcinoma cells with scarcity of mucin granules and intracellular cysts. However, the Y strain never developed antral lesions like the wild strain, developing fundic carcinoid(s) only. Microscopically, these carcinoids contained argyrophilic nonargentaffin granules, and biochemically produced histamine consistently but no 5-hydroxytryptamine (5-HT, serotonin) like those of the wild strain. Since we found unexpectedly that a line of F2 but not F1 hybrids between wild and Z strains developed the same antral lesions as Z strain, a preliminary experiment was performed to confirm the development of antral lesions in F2 hybrids newly produced by brother-sister mating. Among 41 surviving F2 offspring, 4 (9.8%) developed hyperplasia, 2 (4.9%) dysplasia and none adenocarcinoma. The numbers (6) of animals observed with these lesions approximated to their expected numbers (7.3).

Chromosome error propagation and cancer

A general characteristic of tumour cells is their unstable karyotype. It is suggested here that maintenance of the normal diploid cell depends on the presence of two copies of specific genes; a change in gene dosage of one or more of these genes, by chromosome nondisjunction or rearrangement, may trigger a general loss of accuracy in chromosome segregation at mitosis.

Allele loss on short arm of chromosome 17 in breast cancers

Tumour and blood leucocyte DNA from a consecutive series of patients with primary breast cancer was probed to detect deletions at six polymorphic loci in tumour tissue. The highest frequency of allele loss (61%) was found with the probe YNZ22, which detects a sequence on the short arm of chromosome 17 (at p13.3). The previously reported loss of alleles at the Harvey ras locus (11p14) in about 20% of breast tumours was confirmed. The putative breast tumour suppressor gene on 17p may be the same as that already noted for colon and lung cancers and it is suggested that deletion of this gene is one of a cumulative series of lesions involving genetic changes in the evolution of breast cancer. The findings identify chromosome 17p as a candidate region for linkage studies in breast cancer families.