Analysis of genetic changes underlying local recurrence of prostate carcinoma during androgen deprivation therapy

The molecular mechanisms and genetic changes that lead to the progression of prostate cancer during endocrine therapy are poorly characterized. Here, paired specimens from both untreated primary tumors and from local recurrences were collected from 10 prostate cancer patients treated by conventional androgen deprivation therapy. The genetic progression of the tumors was studied by using interphase fluorescence in situ hybridization and chromosome-specific probes. Six primary tumors (60%) and all ten recurrent tumors were aneuploid by fluorescence in situ hybridization. The recurrent tumors also showed a high degree of chromosome copy number variability from one cell to another. Increased copy number of chromosome X was particularly common in the recurrent tumors. In addition, specific high level amplification of the androgen receptor (AR) gene (Xq12) was detected in three highly aneuploid recurrent tumors. Our findings suggest that hormone-refractory prostate cancers are genetically very complex and show intratumor genetic heterogeneity. Increased copy number of chromosome X and the amplification of the androgen receptor (AR) gene may confer proliferative advantage during androgen deprivation and thus contribute to the development of recurrence.

Amplification of chromosomal region 20q13 in invasive breast cancer: prognostic implications

Amplification of the chromosome 20q13 region was recently discovered in breast cancer by comparative genomic hybridization and subsequently further defined by fluorescence in situ hybridization with specific probes. The target gene of the amplification remains unknown. Here, fluorescence in situ hybridization with a cosmid probe for the minimal region of amplification (RMC20C001) was used to study 20q13 amplification in 132 primary breast carcinomas and 11 metastases. The size of the amplicon was studied with four flanking probes. Thirty-eight (29%) primary tumors and 3 (27%) metastases showed increased copy number of the RMC20C001 probe (>1.5-fold relative to the p-arm control). Nine (6.8%) of the primary tumors were highly (>3-fold) amplified. Although the size and location of the amplified region varied from one tumor to another, only the RMC20C001 probe was consistently amplified. 20q13 amplification was significantly associated with a high histological grade (P = 0.01), DNA aneuploidy (P = 0.01), and high S-phase fraction (P = 0.0085). High-level amplification was also associated with short disease-free survival of patients with node-negative breast cancer (P = 0.002). We conclude that high-level 20q13 amplification may be an indicator of poor clinical outcome in node-negative breast cancer and that this chromosomal region is likely to contain a gene with an important role in breast cancer progression. A large definitive study is warranted to assess the independent prognostic value of 20q13 amplification.

Visual mapping by fiber-FISH

FISH techniques have opened new possibilities for high-resolution genome mapping. Effective utilization of these techniques for the rapid orientation and ordering of adjacent and overlapping probes as well as for the characterization of long-range genomic contigs would facilitate physical mapping and positional cloning efforts. Here, we have evaluated our recently developed improved fiber-FISH technique for the physical mapping of a 500-kb region at 1p32 as well as for the detection of genomic rearrangement affecting this region. Our fiber-FISH technique is based on the hybridization of probes to unfixed linearized DNA fibers on a microscope slide. Preparation of the target DNA from cells embedded in pulsed-field gel electrophoresis (PFGE) blocks makes it possible to obtain long intact DNA fibers that give an excellent signal-to-noise ratio in FISH. The linear range of the method reached from 2 to 500 kb with a measuring accuracy approaching that of PFGE. Fiber-FISH was used to establish the order, orientation, and distances for several probes for this region, including six large insert phage, cosmid, and P1 clones and seven genomic subclones. This has significantly facilitated our efforts to develop a genomic contig for this region, recently discovered to contain the gene for inherited neuronal ceroid lipofuscinosis (INCL). Finally, we also demonstrated how rearrangements affecting the L-myc gene at this locus in small-cell lung cancer can be visualized with fiber-FISH. In conclusion, fiber-FISH is very useful for high-resolution physical mapping and contig evaluation as well as for detecting genetic rearrangements.

Genetic aberrations detected by comparative genomic hybridization predict outcome in node-negative breast cancer

Breast cancer progression is determined by a complex pattern of multiple genetic aberrations the association of which with patient prognosis is unknown. In this study, we have undertaken a genome-wide screening to detect genetic changes associated with clinical outcome in node-negative breast cancer. Comparative genomic hybridization was used to screen for DNA sequence gains and losses across all human chromosomes in 23 tumors from node-negative breast cancer patients with no disease recurrence after at least 5 years of follow-up and in 25 node-negative patients with recurrence during the first 5 years of follow-up. The total number of genetic aberrations (copy number gains and losses) per tumor was significantly greater in the recurrence group (P = 0.019) and in the subgroup of these patients who died as a result of breast cancer (P = 0.0022). When copy number losses and gains were analyzed separately, only losses were significant (P = 0.013 for recurrence and P = 0.002 for overall survival). Of the individual loci involved, a high level gain of the long arm of chromosome 8 was significantly associated with recurrence (P = 0.01, Fisher's exact test). Furthermore, amplification of DNA sequences at chromosome 20q12-13 was found in 7 cases (15%), 6 of which had early recurrence within 32 months of diagnosis. This genome-wide overview by comparative genomic hybridization suggests that genetically advanced node-negative breast cancers having a high overall number of genetic aberrations may have a poor prognosis and that increased copy number of two specific regions, 8q and 20q13, may confer a more aggressive phenotype. Results of this pilot study suggest that determination of the total number of DNA sequence copy number aberrations may help therapeutic decision making. Specific probes should be developed to test the prognostic value of 8q and 20q12-13 amplifications in large numbers of patients.

Mechanically stretched chromosomes as targets for high-resolution FISH mapping

When used with metaphase chromosomes, fluorescence in situ hybridization (FISH) makes it possible to localize probes to individual chromosome bands and to establish the order of probes separated by > or = 2-3 Mb in dual-color hybridizations. We evaluated the use of mechanically stretched chromosomes as hybridization targets for increased mapping resolution. Mapping resolution was tested by pair-wise hybridizations with probes from the 1p32-p33 region, spanning distances from 20 to approximately 1500 kb. Probes separated by > or = 170 kb could be ordered relative to one another and to the centromere-telomere axis of the chromosome. The advantages of the technique are the simple procedure for preparing the slides, the straightforward interpretation of the results, and the ability to score the predominant order from < 10 stretched chromosomes. However, because of the variability of stretching from one sample to another, the calculation of actual physical distances between probes is not possible. To illustrate the utility of this method, we showed that the gene for receptor tyrosine kinase TIE lies centromeric to COL9A2, RLF, and L-MYC genes at 1p32. The use of mechanically stretched chromosomes provides < or = 10-fold increased mapping resolution as compared with conventional metaphase FISH. Thus, the technique effectively bridges the gap between metaphase mapping and ultra-high-resolution mapping (1-300 kb) techniques, such as the DNA fiber FISH.

In vivo amplification of the androgen receptor gene and progression of human prostate cancer

Overexpression of amplified genes is often associated with the acquisition of resistance to cancer therapeutic agents in vitro. We have identified a similar molecular mechanism in vivo for endocrine treatment failure in human prostate cancer which involves amplification of the androgen receptor (AR) gene. Comparative genomic hybridization shows that amplification of the Xq11-q13 region (the location), is common in tumours recurring during androgen deprivation therapy. We found high-level AR amplification in seven of 23 (30%) recurrent tumours, but in none of the specimens taken from the same patients prior to therapy. Our results suggest that AR amplification emerges during androgen deprivation therapy by facilitating tumour cell growth in low androgen concentrations.

Identification of gains and losses of DNA sequences in primary bladder cancer by comparative genomic hybridization

Comparative genomic hybridization (CGH) makes it possible to detect losses and gains of DNA sequences along all chromosomes in a tumor specimen based on the hybridization of differentially labeled tumor and normal DNA to normal human metaphase chromosomes. In this study, CGH analysis was applied to the identification of genomic imbalances in 26 bladder cancers in order to gain information on the genetic events underlying the development and progression of this malignancy. Losses affecting 11p, 11q, 8p, 9, 17p, 3p, and 12q were all seen in more than 20% of the tumors. The minimal common region of loss in each chromosome was identified based on the analysis of overlapping deletions in different tumors. Gains of DNA sequences were most often found at chromosomal regions distinct from the locations of currently known oncogenes. The bands involved in more than 10% of the tumors were 8q21, 13q21-q34, 1q31, 3q24-q26, and 1p22. In conclusion, these CGH data highlight several previously unreported genetic alterations in bladder cancer. Further detailed studies of these regions with specific molecular genetic techniques may lead to the identification of tumor suppressor genes and oncogenes that play an important role in bladder tumorigenesis.

A physical map of chromosome 20 established using fluorescence in situ hybridization and digital image analysis

The physical locations of 46 cosmid clones and 21 P1 clones were determined along the chromosome 20 axis relative to the p terminus (FLpter) using fluorescence in situ hybridization (FISH) and digital image microscopy. The cosmid clones were selected from the chromosomally enriched library LA20NC01. Nine P1 clones were selected from a pooled DuPont genomic library using PCR with primer pairs selected to amplify genetically mapped sequence-tagged sites. This information was used to relate the physical map to the genetic map. Twelve P1 clones were selected from the same library using PCR primer pairs that amplified known genes. Two of these, E2F and BCLX, had not been mapped previously.

Aggressiveness of screen-detected breast cancers

It is not clear whether screening for breast cancer works as public health policy and whether early indicators of effect predict an ultimate reduction in mortality. The malignant potentials of 248 breast cancers detected by the screening service in Finland were compared with those of 490 control cancers diagnosed before the screening service was established. Aggressiveness was assessed by DNA flow cytometry and clinical status by cancer size and node involvement. After the first screening round, the results of DNA flow cytometry were the same in cancers diagnosed by screening and in controls; these findings are consistent with the hypothesis that the biological aggressiveness of breast cancer remains constant as the cancer progresses. The proportion of patients with node-negative and small T1 cancers after the first screening was higher among the screened population than among controls, indicating earliness of diagnosis among those screened. Cancers diagnosed in the first round had a low malignant potential, as indicated by the DNA flow-cytometry and by clinical stage. Lower aggressiveness of cancers found by screening than of control cancers would indicate overdiagnosis or length-biased sampling, but not earliness of diagnosis. Screening with mammography is practised as a public-health policy in Finland. The results predict that the mortality reduction found in randomised trials can be repeated with a screening service.

Genetic changes in primary and recurrent prostate cancer by comparative genomic hybridization

Genetic changes leading to the development of prostate cancer and factors that underlie the clinical progression of the disease are poorly characterized. Here, we used comparative genomic hybridization (CGH) to screen for DNA sequence copy number changes along all chromosomes in 31 primary and 9 recurrent uncultured prostate carcinomas. The aim of the study was to identify those chromosome regions that contain genes important for the development of prostate cancer and to identify genetic markers of tumor progression. CGH analysis indicated that 74% of primary prostate carcinoma showed DNA sequence copy number changes. Losses were 5 times more common than gains and most often involved 8p (32%), 13q (32%), 6q (22%), 16q (19%), 18q (19%), and 9p (16%). Allelic loss studies with 5 polymorphic microsatellite markers for 4 different chromosomes were done from 13 samples and showed a 76% concordance with CGH results. In local recurrences that developed during endocrine therapy, there were significantly more gains (P < 0.001) and losses (P < 0.05) of DNA sequences than in primary tumors, with gains of 8q (found in 89% of recurrences versus 6% of primary tumors), X (56% versus 0%), and 7 (56% versus 10%), as well as loss of 8p (78% versus 32%), being particularly often involved. In conclusion, our CGH results indicate that losses of several chromosomal regions are common genetic changes in primary tumors, suggesting that deletional inactivation of putative tumor suppressor genes in these chromosomal sites is likely to underlie development of prostate cancer. Furthermore, the pattern of genetic changes seen in recurrent tumors with the frequent gains of 7, 8q, and X suggests that the progression of prostate cancer and development of hormone-independent growth may have a distinct genetic basis. These chromosome aberrations may have diagnostic utility as markers of prostate cancer progression.

Hardware and software requirements for quantitative analysis of comparative genomic hybridization

Recommendations are made for hardware and software capabilities that will permit a level of performance of comparative genomic hybridization (CGH) analysis on metaphase chromosomes that is comparable to the best current practice. Guidelines for interpreting the results of CGH analysis in terms of chromosomal gains or losses are also presented.

Computer image analysis of comparative genomic hybridization

We describe and evaluate the image-processing and analysis techniques we have developed for the quantitative analysis of comparative genomic hybridization (CGH; Science 258:818, 1992). In a typical CGH application, two genomic DNA samples are simultaneously hybridized to metaphase chromosomes and detected with different fluorochromes. The primary data in CGH are contained in the intensity ratios of the fluorochromes as a function of position on the chromosomes, which reflect variation in DNA copy number ratio between the two DNA samples. Analysis involves chromosome segmentation, intensity normalization, background corrections, and calculation of the fluorescence intensity profiles and the ratio profile along the chromosome's length. Profiles from several copies of the same chromosome in different metaphases are averaged to reduce the noise. Confidence intervals are calculated and displayed for the mean profiles. The techniques were evaluated by examining the variability found in comparisons of two normal genomic DNAs, where the ratio was expected to be constant, and by measuring the ratios obtained for cell lines with cytogenetically documented copy number changes involving several chromosomal segments. The limits of sensitivity of CGH analysis were investigated by simulation. Guidelines for the interpretation of CGH data and indications of areas for future development of the analytical techniques are also presented.

The human gene for xanthine dehydrogenase (XDH) is localized on chromosome band 2q22

Mutations in the xanthine dehydrogenase gene (XDH), which codes for the last enzyme of the purine catabolic pathway in man, cause the autosomal recessive disease xanthinuria. We obtained cDNA clones from a human breast cDNA library and confirmed one of the two different sequences proposed for human XDH. Using a somatic cell hybrid mapping panel and specific primers for human XDH, we assigned the gene to chromosome 2. By fluorescence in situ hybridization, the gene was localized to bands 2p22.3-->p22.2. The FLpter probe location was 0.135 (SD = 0.016), as determined by digital image analysis.

High resolution mapping using fluorescence in situ hybridization to extended DNA fibers prepared from agarose-embedded cells

Fluorescence in situ hybridization (FISH) and pulse field gel electrophoresis (PFGE) are essential techniques in physical mapping and in positional cloning. We present a technique that utilizes agarose-embedded high molecular weight DNA prepared for PFGE as a target for FISH. The agarose blocks are melted, and the DNA is extended on a poly-L-lysine-coated microscope slide. The resulting DNA fibers appear on the slide as long straight strands and are a suitable target for high resolution FISH mapping as demonstrated here with cosmid and plasmid hybridizations.

Sensitive detection of chromosome copy number aberrations in prostate cancer by fluorescence in situ hybridization

The pattern of chromosomal aberrations and their significance in prostate cancer are poorly understood. We studied 23 prostate cancer and 10 benign prostatic hyperplasia (BPH) specimens by fluorescence in situ hybridization (FISH) using pericentromeric repeat-specific probes for 10 different chromosomes. The aims of the study were: 1) to compare the sensitivity of FISH and DNA flow cytometry in aneuploidy detection, 2) to determine which chromosome copy number changes are most common, and 3) which probe combinations would be most effective in aneuploidy diagnosis. Disaggregated tumor cells from formalin-fixed, paraffin-embedded tissues were pretreated with our newly developed method based on hot glycerol solution to improve probe penetration. All BPH specimens were diploid by DNA flow cytometry and showed no numerical chromosome aberrations by FISH. In prostate cancer, flow cytometry showed abnormal DNA content in 35% of cases, whereas 74% were abnormal by FISH. Aberrant copy number of chromosomes 8 (48% of cases), X (43% of cases), and 7 (39% of cases) were most common. Ninety-four percent of all aneuploid cases would have been detected with these three probes alone. Simple chromosome losses were uncommon but in DNA tetraploid tumors relative losses (trisomy or disomy) of several chromosomes were often found, suggesting progression of prostate cancer through tetraploidization followed by losses of selected chromosomes. In conclusion, our results indicate that FISH using three selected chromosome-specific probes is two to three times more sensitive than flow cytometric DNA content analysis in aneuploidy detection.

Optimizing comparative genomic hybridization for analysis of DNA sequence copy number changes in solid tumors

Comparative genomic hybridization (CGH) is a powerful new method for molecular cytogenetic analysis of cancer. In a single hybridization, CGH provides an overview of DNA sequence copy number changes (losses, deletions, gains, amplifications) in a tumor specimen and maps these changes on normal chromosomes. CGH is based on the in situ hybridization of differentially labeled total genomic tumor DNA and normal reference DNA to normal human metaphase chromosomes. After hybridization and fluorescent staining of the bound DNAs, copy number variations among the different sequences in the tumor DNA are detected by measuring the tumor/normal fluorescence intensity ratio for each locus in the target metaphase chromosomes. CGH is in particular useful for analysis of DNA sequence copy number changes in common solid tumors where high-quality metaphase preparations are often difficult to make, and where complex karyotypes with numerous markers, double minutes, and homogeneously stained chromosomal regions are common. CGH only detects changes that are present in a substantial proportion of tumor cells (i.e., clonal aberrations). It does not reveal translocations, inversions, and other aberrations that do not change copy number. At present, CGH is a research tool that complements previous methods for genetic analysis. CGH will advance our understanding of the genetic progression of cancer and highlight important genomic regions for further study. Direct clinical applications of CGH are possible, but will require further development and validation of the technique. We describe here our recent optimized procedures for CGH, including DNA labeling, hybridization, fluorescence microscopy, digital image analysis, data interpretation, and quality control, emphasizing those steps that are most critical. We will also assess sensitivity and resolution limits of CGH as well as discuss possible future technical improvements.

Automated peak detection and cell cycle analysis of flow cytometric DNA histograms

We describe an algorithm for fully automated flow cytometric DNA histogram classification and analysis that provides rapid, reproducible determination of DNA index and S-phase fraction (SPF). Automated classification agreed with subjective assessment of DNA ploidy in 96-98% of DNA histograms. Automated and conventional analyses of DNA index (r = 0.95) and SPF (r = 0.89) were also highly correlated with one another. In a series of 86 node-negative breast carcinomas, SPF calculated with the fully automated method was a significant predictor of 10 year survival (p = 0.009). Automation greatly increased the speed of DNA histogram analysis, allowing evaluation of the same set of histograms with different methods. In a preliminary study exploring the optimization of DNA histogram analysis, the best association between SPF and prognosis of breast cancer patients was achieved using sliced nuclei debris modeling, reporting only the aneuploid SPF (in aneuploid histograms), while excluding small aneuploid clones (< 15% of total cell count) from evaluation. In conclusion, automated DNA histogram analysis does not replace the need for close human supervision but provides a useful guideline for less experienced users, facilitates interlaboratory comparisons, and makes possible extensive reanalyses of large data sets.

Improved technique for analysis of formalin-fixed, paraffin-embedded tumors by fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) and specific DNA probes for peri-centromeric repeat regions and unique sequence loci have made it possible to study chromosomal aberrations from interphase tumor nuclei. Large-scale retrospective studies on the prognostic value of interphase cytogenetics would become feasible if these techniques were readily applicable to nuclei from archival formalin-fixed tumor tissues. We describe here an improved technique for interphase FISH analysis of tumors that have been extensively fixed in formalin. The protocol aims at improving probe penetration and hybridization efficiency by inducing chromatin decondensation and swelling of the nuclei with a heat treatment in a 90 degrees C glycerol solution prior to hybridization. Using this cell pretreatment, FISH results on the detection of chromosome copy number aberrations and amplification of the c-erbB-2 oncogene from formalin-fixed, paraffin-embedded tissues were highly concordant with those from fresh tissues. In contrast to previously described methods, separate adjustments of denaturation or proteinase K digestion are not required for each sample. This method facilitates retrospective analyses of large series of tumors and is also useful for applying FISH to routine diagnostic purposes using formalin-fixed material.

Detection and mapping of amplified DNA sequences in breast cancer by comparative genomic hybridization

Comparative genomic hybridization was applied to 5 breast cancer cell lines and 33 primary tumors to discover and map regions of the genome with increased DNA-sequence copy-number. Two-thirds of primary tumors and almost all cell lines showed increased DNA-sequence copy-number affecting a total of 26 chromosomal subregions. Most of these loci were distinct from those of currently known amplified genes in breast cancer, with sequences originating from 17q22-q24 and 20q13 showing the highest frequency of amplification. The results indicate that these chromosomal regions may contain previously unknown genes whose increased expression contributes to breast cancer progression. Chromosomal regions with increased copy-number often spanned tens of Mb, suggesting involvement of more than one gene in each region.

Physical mapping of chromosome 17 cosmids by fluorescence in situ hybridization and digital image analysis

We used fluorescence in situ hybridization and digital image analysis to localize cosmids along human chromosome 17. Seventy-one cosmids were selected at random from a chromosome 17 library constructed from a partial Sau3AI digest of flow-sorted chromosomes from a mouse-human hybrid cell line. Sixty-three of these (89%) gave a signal only on chromosome 17. The 40 cosmids producing the most distinct hybridization signals in metaphase and interphase cells were precisely mapped using digital image analysis. An additional 20 cosmids, previously mapped by linkage analysis, were also mapped. The order of these probes determined by metaphase mapping was consistent with the order determined by linkage analysis.

Elevated erbB-2 oncoprotein levels in preoperative and follow-up serum samples define an aggressive disease course in patients with breast cancer

BACKGROUND

Recent evidence indicates that a soluble fragment of the erbB-2 oncogene product may be released from cell surface and become detectable in the serum of patients with breast cancer.

METHODS

To study the diagnostic utility of this phenomenon, the authors measured serum erbB-2 levels with a quantitative enzyme-linked immunosorbent assay in 227 preoperative samples from women who underwent breast surgery and in 339 samples from 225 patients with breast cancer during follow-up.

RESULTS

Eleven (9%) of 114 preoperative samples from patients with a histologically verified breast cancer and 2 of 113 (1.8%) from patients with benign breast tumors had elevated (greater than 20 U/ml) serum erbB-2 antigen levels. Ten (91%) of the 11 carcinomas and one of the benign tumors from patients with elevated serum erbB-2 levels also showed overexpression of the erbB-2 protein in immunohistochemical analysis of tissue sections. Elevated preoperative serum erbB-2 levels were predominantly found in patients with large tumors, and those with axillary lymph node or distant metastases. Sixty-three of the 339 (19%) follow-up samples had elevated serum erbB-2 antigen levels. Approximately one-third (30.9%) of the samples taken during recurrent disease were serum erbB-2 positive, which is close to the overall overexpression rate of this oncogene. Elevated erbB-2 levels were more common in patients whose disease was not responsive to treatment. Patients with distant metastases had elevate erbB-2 levels more often (40%) than did those with locoregional recurrence (20%). Elevated erbB-2 levels predicted the appearance of metastases within the next 6 months in 10 of 27 (37%) patients.

CONCLUSION

The study's results suggest that assay serum erbB-2 levels may be valuable in the follow-up and monitoring of patients with breast cancer whose primary tumors show erbB-2 overexpression by immunohistochemistry.

Molecular cytogenetics of human breast cancer

Our studies of human breast cancer using CGH and FISH with precisely mapped probes have revealed a surprising amount of intratumor and intertumor heterogeneity in human breast cancers. However, some regions of abnormal copy number are found frequently. We believe that the regions of frequent abnormality harbor novel cancer genes, and that identification of these is important for diagnosis, prognostication, and the development of new therapies.

Prognostic value of cells with more than 5c DNA content in node-negative breast cancer as determined by image cytometry from tissue sections

The aim of this investigation was to study the prognostic significance of 5c cells (presence of cancer cells with > 5c DNA content; ie, over 18 pg of DNA per nucleus) in axillary node-negative breast cancer. Tissue sections (3 microns) from 134 tumors were stained for DNA using the Feulgen method and screened for the percentage of 5c cells with the CAS 200 image analysis system (Cell Analysis System, Inc, Lombard, IL). Cancer cells with a DNA content exceeding the 5c level were found in 45% (60 of 134) of the cases, accounting for a median of 0.2% (range, 0.05% to 1.05%) of all cells. The presence of 5c cells was associated with a high histologic grade of the tumor (P = .0001), a large number of mitoses (P < .0001), flow cytometric DNA aneuploidy and high S-phase fraction (P = .0002 and P < .0001, respectively), and c-erbB-2 oncoprotein and p53 tumor suppressor gene product overexpression (P = .0002 and P = .0006, respectively). Patients with 5c cell-positive tumors had a significantly worse 8-year survival rate (P = .003) than those with 5c cell-negative tumors. Subgroup analysis showed that the presence of 5c cells had a prognostic impact in low malignancy tumors, ie, in well-differentiated (grade I or II) and slowly proliferating tumors. Our findings suggest that determination of 5c cells may be a useful additional prognostic factor in axillary node-negative breast cancer. It adds prognostic information, especially in cases that are otherwise thought to have a favorable course.

Extrachromosomal gene amplification in acute myeloid leukemia; characterization by metaphase analysis, comparative genomic hybridization, and semi-quantitative PCR

A case of acute myeloid leukemia (M-3) with complex karyotypic aberrations and double minute (dmin) chromosomes is presented. The patient had no history of prior exposure to mutagenic or carcinogenic agents or of other malignancies. She died from CNS involvement six weeks after the initial diagnosis. We used comparative genomic hybridization to identify the amplified sequences presumed to represent the dmin of the leukemic cells; the tumor/normal ratios indicated increased signal intensity at 8q24. This localization prompted investigation by semi-quantitative PCR that revealed amplification of the MYC oncogene. The extent of chromosome aberrations and the oncogene amplification, both linked with poor prognosis, may relate to the rapid course of this patient's disease.