Molecular detection of tumor cells in bronchoalveolar lavage fluid from patients with early stage lung cancer

Quantitative GSTP1 methylation clearly distinguishes benign prostatic tissue and limited prostate adenocarcinoma

PURPOSE

Hypermethylation of the glutathione S-transferase gene (GSTP1) is the most common (greater than 90%) reported epigenetic alteration in prostate cancer. It occurs early in cancer progression and it is a promising marker for detecting organ confined disease. To evaluate its use as a diagnostic tool for cancer we used quantitative GSTP1 methylation to test for the presence of cancer in 45 prostate needle biopsy samples.

MATERIALS AND METHODS

Paraffin tissue samples from 45 patients with minute foci of intermediate grade prostatic adenocarcinoma or benign disease on needle biopsy were tested for GSTP1 hypermethylation using quantitative fluorogenic real-time methylation specific polymerase chain reaction. This assay was performed in blinded fashion without previous knowledge of the histopathological diagnosis.

RESULTS

DNA from 29 of the 45 paraffin samples was amenable to polymerase chain reaction amplification. In these 29 samples GSTP1 methylation was detected in 11 of 15 cases of limited cancer and in 0 of 14 of benign disease (2-sided Fisher's exact test, p <0.0001). Thus, this assay had 73% sensitivity, 100% specificity, 100% positive and 78% negative predictive values.

CONCLUSIONS

Quantitation of GSTP1 hypermethylation accurately detects the presence of cancer even in small, limited tissue samples. It represents a promising diagnostic marker that could be used as an adjunct to tissue biopsy as part of prostate cancer screening.

Comparison of K-ras gene mutations in tumour and sputum DNA of patients with lung cancer

Mutations in the K-ras gene are frequently found in lung tumours and are implicated in the development of lung cancer. In order to investigate the clinical usefulness of these mutations in lung cancer, we applied a sensitive method to compare mutations in codon 12 of the K-ras gene in DNA extracted from lung tumours and the matched sputum samples obtained from 22 lung cancer patients. K-ras mutations were identified in the lung tumours of 12 patients (54.5%) and in the sputum samples of 10 patients (45.5%). Nine patients showed an identical mutation in both the tumour and the matched sputum samples. There was a significant association between the presence of a K-ras mutation in a lung tumour and the detection of an identical mutation in the matched sputum sample of the lung cancer patient (kappa = 0.64, 95% confidence interval 0.32-0.95, p <0.01). K-ras mutations were detected in sputum samples from cancer patients with all lung tumour grades, and both in the presence and the absence of lymph node metastasis. Therefore, K-ras mutations may provide useful diagnostic markers for lung cancer.

The TP53 gene, tobacco exposure, and lung cancer

Of the various genetic alterations in lung cancer, the abnormalities of the TP53 gene (p53) are among the most frequent and important events. Because of its importance, many aspects of TP53 have been studied, including preneoplastic lesions and TP53as a marker for early detection and prognosis and as a therapeutic option. We summarize recent knowledge of TP53 in lung cancer with a special emphasis on the relationship between smoking exposure (e.g, cigarette, etc.) and specific mutational pattern of TP53by analyzing the latest version of the International Agency for Research on Cancer (IARC) database on TP53 mutations in human cancer. Our analysis confirmed several other studies showing significant differences in the frequencies of G:C to T:A transversions between ever-smokers and never-smokers. Furthermore, when comparing the mutational spectrum by gender, important differences were noted between male and female never-smokers. We concluded that the previously noted G:C to T:A transversions were mainly due to female smokers having a high frequency of these changes compared to female never-smokers. There was no relationship between adenocarcinomas and squamous cell carcinomas independent of gender. We also examined the seven codons which have been previously identified as hot spots, that is, the sites of frequent G:C to T:A transversions in smoking-related lung cancers. However, there was no specific codon which was strongly related to smoke exposure despite a moderate relationship. We considered the term "warmspot" may be more appropriate. While mutations of TP53 are frequent in lung cancers, further investigation is necessary to understand their role for lung carcinogenesis, especially as they relate to gender differences, and to translate our laboratory knowledge to clinical applications.

DNA methylation, a biomarker for colorectal cancer: implications for screening and pathological utility

Currently up to one-third of colorectal cancer patients present with locally advanced or metastatic disease that precludes a surgical cure. Performance limitations and low uptake of current screening tools have fueled research to develop minimally invasive approaches that can detect early-stage neoplasms. The observation that altered DNA can be amplified from the stool or circulation has stimulated research on its use as a biomarker of occult neoplasia. De novo methylation of CpG islands 5' to certain tumor suppressor genes has been associated with epigenetic silencing. At certain loci this phenomenon is specific for neoplastic populations, and it is frequently detected at early stages in colorectal tumorigenesis. Accordingly, hypermethylation events have been proposed by researchers as ideal targets for the basis of a screening panel to detect peripheral tumor DNA. This critique reviews research findings on the use of epigenetic biomarkers in screening for occult neoplasia. In addition, the authors consider the pathological utility of epigenetic testing in refining tumor staging and predicting disease recurrence.

DNA methylation as a cancer-specific biomarker: from molecules to populations

Cancer contributes to a large proportion of the mortality and morbidity in the United States and worldwide. Despite advances in diagnosis and treatment of various cancers, early detection and treatment of cancer remain a challenge. Diagnosis of cancer often occurs once the disease has progressed to a point where currently available intervention options provide limited success. Therefore, techniques that enable early detection followed by targeted interventions would influence stage at diagnosis and, in turn, mortality associated with cancer. Identification of molecular biomarkers, especially those that are associated with cancer initiation and progression, shows promise as an effective strategy in this regard. One potential early detection biomarker is DNA methylation of the promoter region of certain cancer-associated genes, which results in gene inactivation. Examination of serum for circulating tumor DNA with abnormal methylation patterns offers a possible method for early detection of several cancers and serves as a point for early intervention and prevention strategies. Additionally, it is imperative to consider how such a screening mechanism can be implemented in populations at risk, especially in resource-poor settings. Thus, the challenge is to validate DNA methylation as a cancer-specific biomarker, with the ultimate goal of designing a research plan that integrates the current knowledge base regarding cancer detection and diagnosis into specific prevention and intervention strategies that can be applied at a population level.

Mutations of the D310 mitochondrial mononucleotide repeat in primary tumors and cytological specimens

A mononucleotide repeat (D310) in mitochondrial DNA has been recently identified as a mutational hot spot in primary tumors. We analyzed 56 tumors for insertion/deletion mutations in the D310 repeat. A total of 13 mutations were detected. The highest frequency of mutations was found for cervical cancer, followed by bladder tumors, breast cancer and endometrial neoplasia. No alterations were observed in four patients suspected of malignancy but without evidence of malignant tumor. We detected identical changes in four of four urine sediments from patients with bladder cancer and in three of three fine needle aspirates of patients with breast cancer. Our results indicate that D310 abnormalities are detectable in cytology specimens from patients with cancer and support the notion that D310 analysis may represent a new molecular tool for cancer detection.

New approaches for biomarker discovery in lung cancer

Lung cancer remains the most common cause of cancer death in the US and worldwide. Currently, there is no implemented population-based screening for lung cancer. Of all the markers identified, none have achieved sufficient diagnostic significance to reach clinical application. Here we discuss the status of lung cancer early diagnostics, and the genomic and proteomic approaches currently undertaken for biomarker discovery. We then introduce the ANTIBIOMIX approach that enables high-throughput target discovery by interrogating biological samples using a collection of thousands of polyclonal antibodies. The development of specific and sensitive diagnostic assays using patient's biological fluids, such as sputum and serum, will improve screening, monitoring of disease progression and treatment response, and surveillance for recurrence.

Endothelin B receptor gene hypermethylation in prostate adenocarcinoma

BACKGROUND

Alterations in the methylation patterns of promoter CpG islands have been associated with the transcriptional inhibition of genes in many human cancers. These epigenetic alterations could be used as molecular markers for the early detection of cancer-that is, while potentially curable according to current therapeutic strategies. In prostate cancer, GSTP1 hypermethylation is the most common epigenetic alteration, and can be detected in up to 90% of cases. Thus, screening for methylation of other loci would probably increase the number of primary tumours amenable to screening. Moreover, previous studies have shown that the endothelin B receptor (EDNRB) gene is abnormally methylated in a high proportion of prostate tumours ( approximately 70%).

AIMS

To investigate the potential use of EDNRB gene hypermethylation as a prostate cancer specific marker.

METHODS

Methylation specific polymerase chain reaction (MSP) for the promoter region of EDNRB was performed on prospectively collected tissue samples from 48 patients harbouring clinically localised prostate cancer, and in a group of 23 patients with benign prostatic hyperplasia (BPH). Genomic DNA was isolated from the samples and the methylation status was examined in a blinded manner.

RESULTS

EDNRB methylation was found in 40 of 48 of the adenocarcinomas. However, the same alteration was found in the paired normal tissue, and 21 of 23 of the BPH samples were found to harbour EDNRB hypermethylation.

CONCLUSIONS

EDNRB hypermethylation at CpG sites upstream of the transcription start site can be detected in a high proportion of prostate adenocarcinomas. However, because this same alteration is also present in normal and hyperplastic tissue, it does not distinguish normal from neoplastic prostate cells, thus precluding its use as a prostate cancer marker.

Detecting lung cancer in plasma with the use of multiple genetic markers

Recent studies have demonstrated the possibility to detect genetic changes in plasma DNA of cancer patients. The goal of this study was to validate a panel of molecular markers for lung cancer detection in plasma DNA. Three markers, p53, FHIT and microsatellite alterations at loci on chromosome 3, were used to detect mutations in tumor and plasma DNA of 64 stage I-III non small cell lung cancer patients. p53 mutations were studied by direct sequencing of exons 5 through 8 in tumor DNA and by plaque hybridization assay and sequencing in plasma DNA. Allelic losses were evaluated by fluorescent PCR in tumor and plasma DNA. p53 genomic mutations were detected in 26 (40.6%) of 64 tumor DNA samples and the identical mutation was identified in plasma of 19 (73.1%) of them. Microsatellite alterations at FHIT and 3p loci were observed in 40 (62.5%) tumors and in 23 (35.9%) plasma samples. Of the 40 patients showing microsatellite alterations in tumors, 19 (47.5%) displayed the same change in plasma DNA. At least 1 of the 3 genetic markers (p53, FHIT and 3p) was altered in plasma of 51.6% of all patients and 60.7% of stage I patients. Moreover, genetic markers in plasma identified 29 of 45 (64.4%) of all stages and 15 of 22 (68.2%) of stage I patients whose tumors had an alteration. These results provide the proof of principle that plasma DNA alterations are tumor-specific in most cases and support blood testing as a noninvasive strategy for early detection.

Molecular approaches to lung cancer evaluation

The stagnation of therapeutic results in lung cancer over the last decade(s) is a matter of great concern, also due to the constantly increasing incidence of the disease. Among the reasons for this failing therapeutic progress is the lack of understanding of the molecular mechanisms underlying the disease. Presently molecular biology techniques contribute to the deciphering of these mechanisms. This review article gives an overview of the actual situation. The genetic changes leading to malignancy are successively considered at the DNA, RNA and protein levels. Alterations at the DNA level represent the bulk of the available data, being related to p53 mutations, alterations in the beta-tubulin gene, microsatellite alterations, methods for identifying individual and isolated aberrant cells, identification of epigenetic mechanisms such as methylation of the promoter region of tumor suppressor genes; alterations in pre-neoplastic lesions are also evoked. In all cases, the techniques are described and results presented. RNA based methods are critically considered, and the yeast functional assay described. Protein based methods are also considered. The use of cDNA microarrays opens new perspectives and brings the simultaneous identification of numerous DNA alterations at a grip, with hopefully significant improvements in treatment results and increased efficiency for early detection and prevention.

Quantitative GSTP1 hypermethylation in bodily fluids of patients with prostate cancer

OBJECTIVES

To further determine the value of real-time quantitative methylation-specific polymerase chain reaction (MSP) of GSTP1 as a molecular tool for the detection of prostate adenocarcinoma. Recent studies have shown a high frequency (more than 90%) of GSTP1 gene promotor methylation in prostate adenocarcinoma and a lower frequency in DNA from serum and urine.

METHODS

Tissue samples from 69 patients with early-stage prostate adenocarcinoma and 31 patients with benign prostatic hyperplasia were collected. Matched urine and plasma specimens were obtained preoperatively. After sodium-bisulfite treatment, extracted DNA was analyzed for GSTP1 promoter hypermethylation both by conventional and real-time quantitative MSP.

RESULTS

In tissue samples, GSTP1 hypermethylation was detected in 63 (91.3%) of the 69 patients with cancer and in 9 (29%) of the 31 patients with benign prostatic hyperplasia. Conventional MSP detected GSTP1 hypermethylation in a larger number of urine and plasma samples than did real-time quantitative MSP (53.6% versus 31.9%, overall). In all positive bodily fluids, the paired tumor was also confirmed to be methylated. GSTP1 hypermethylation was detected by both MSP methods in only one urine sample (3.2%) from a patient with benign prostatic hyperplasia.

CONCLUSIONS

Although not quantitative, conventional MSP is currently more sensitive than real-time quantitative MSP in the detection of GSTP1 hypermethylation in bodily fluids from patients with prostate cancer with clinically localized disease. The value of quantitative determinations in monitoring and risk assessment remains to be further explored.

Lung cancer. 1: prevention of lung cancer

Cancer of the lung causes more deaths from cancer worldwide than at any other site. The environmental, genetic, and dietary risk factors are discussed and progress in chemoprevention is reviewed. A better understanding of the molecular events that occur during carcinogenesis has opened up new areas of research in cancer prevention and a number of biochemical markers of high risk individuals have been identified. It is predicted that greater success in chemoprevention will be achieved in the next decade than in the last.

Is cancer really a 'local' cellular clonal disease?

Cancer is not simply the result of specific genetic alterations in key regulatory genes, but rather a complex multistep process involving selection of a clonal population of cells. To accumulate three, or often as many as seven, specific mutations in a single cell without incurring a significant number of additional mutations that might lead to cell lethality requires a large number of target cells, some mutagenic activity acting on those target cells for a variable period of time, and efficient selection strategies, which may be to some extent tissue-specific. A number of 'protective' intracellular regulatory circuits might be present in proliferating cells deliberately to protect against carcinogenesis. If it does require some seven sequential carcinogenic 'genetic hits' in a single cellular clone for a malignant tumor to develop, it is mathematically more likely to occur in a tissue with a high background of genetic alterations in neighboring cellular clones, than in a tissue with a low background of such alterations, or with no detectable carcinogenic mutations at all. In this context, the old 'field cancerization' theory by Slaughter and the more recent 'multistep carcinogenesis' model by Fearon and Vogelstein can come together in a single model: 'multistep field cancerization'. This simple conclusion, and our ability to measure 'background carcinogenesis' in different parts of the body, might allow early detection of cancer risk, and eventually help us to develop suitable therapeutic strategies to delay or suppress the carcinogenic process. Molecular technologies are just beginning to be sufficiently sensitive to start testing the hypothesis.

A fluorescence in situ hybridization-based assay for improved detection of lung cancer cells in bronchial washing specimens

BACKGROUND

Interphase fluorescence in situ hybridization (FISH) is a powerful tool for detecting chromosome and locus-specific changes in tumor cells. We developed a FISH-based assay to detect genetic changes in bronchial washing specimens of lung carcinoma patients.

METHODS

The assay uses a mixture of fluorescently labeled probes to the centromeric region of chromosome 1 and to the 5p15, 8q24 (site of the c-myc gene), and 7p12 (site of the EGFR gene) loci to assess cells in bronchial washing specimens for chromosomal abnormalities indicative of lung carcinoma. The FISH assay was performed on 74 specimens that had been assessed previously for evidence of malignancy by routine cytology with Pap staining.

RESULTS

Forty-eight patients had histologically confirmed lung carcinoma and 26 patients had a clinical diagnosis that was negative for lung carcinoma. FISH analysis was performed without knowledge of the patient's clinical information. The finding of six or more epithelial cells with gains of two or more chromosome regions was considered a positive FISH result (i.e., evidence of malignancy). The sensitivity of FISH for the detection of lung carcinoma was 82% in this set of specimens compared with a 54% sensitivity by design for cytology (FISH vs. cytology, P = 0.007). FISH detected 15 of 18 specimens that were falsely negative by cytology. The specificities of FISH and cytology were 82% and 100%, respectively, and were not significantly different (P = 0.993).

CONCLUSIONS

The data indicate a potential utility of the FISH assay as an adjunct to bronchial washing cytology in routine clinical practice.

Smoking molecular damage in bronchial epithelium

Our understanding of the molecular pathology of lung cancer is advancing rapidly with several specific genes and chromosomal regions being identified. Lung cancer appears to require many mutations in both dominant and recessive oncogenes to possess malignant phenotypes. Several genetic and epigenetic changes are common to all lung cancer histologic types, while others appear to be cell type specific. However, specific roles of the genes undergoing mutations and the order of cumulative molecular changes that lead to the development of each lung tumor histologic type remain to be fully elucidated. Recent findings of molecular abnormalities in normal appearing and preneoplastic bronchial epithelium from patients with lung cancer and chronic smokers suggest that genetic changes may serve as biomarkers for early diagnosis, risk assessment and monitoring response to chemoprevention.

Molecular detection approaches for smoking associated tumors

Smoking is directly responsible for approximately 90% of lung cancers and is also strongly associated with cancers of the head and neck, esophagus and urinary bladder. Our growing understanding of the molecular changes that underlie cancer progression has contributed to the development of novel molecular approaches for the detection of cancer. In this study, we review a number of recent studies that have used molecular techniques to detect neoplastic DNA from lung, head and neck, esophagus and bladder cancer. The majority of these approaches are based on polymerase chain reaction (PCR) based assays. These PCR-based techniques can detect a few clonal cancer cells containing a specific DNA mutation, microsatellite alteration, or CpG island methylation among an excess background of normal cells. The ability to accurately detect a small number of malignant cells in a wide range of clinical specimens including sputum, saliva, bronchoalveolar lavage fluid, urine, serum, plasma, or tissue has significant implications for screening high-risk individuals (such as cigarette smokers) for cancer.

Recent advances in the molecular diagnosis of lung cancer

Despite extensive effort in improvement of diagnosis and treatment of patients with lung cancer in past three decades, the overall survival of patients with the disease remains dismal. Because the development of lung cancer takes a few decades, early diagnosis of the disease or identification of truly high-risk populations may provide us opportunity to successfully cure or prevent the disease. Recent advances in understanding biological basis of lung tumorigenesis provide new tools for detecting malignant cells or the process of malignant transformation and progression. Along with identification of molecular abnormalities in the early lung tumorigenesis, advanced molecular analytic technologies have been emerged, which may facilitate development of rapid and effective methods for early diagnosis and risk assessment. Here, I discuss recent progresses in understanding of early molecular abnormalities in lung cancer, efforts of translating laboratory findings to clinical tests, and prospective of biomarkers in lung cancer diagnosis and risk assessment.

Innovative molecular and imaging approaches for the detection of lung cancer and its precursor lesions

Current approaches for the therapy of lung cancer, the majority of which being advanced cancers, have failed to impact on long term survival. The key to improvement lies in the combination of early diagnosis and the introduction of novel targeted therapies. In this article we review some of the innovative approaches, both imaging and molecular, that are currently under investigation for early detection. Because lung cancers may arise in the central or peripheral compartments of the lung, newer approaches must target tumours arising in both of these compartments. Specimens available for analysis include sputa and blood. Detection of genetic changes in peripheral blood is a promising avenue being explored by several groups. Molecular techniques discussed include gene mutations, detection of nuclear riboprotein, methylation related silencing of genes and malignancy associated changes. Newer imaging technologies include autofluorescence bronchoscopy, virtual bronchoscopy, optical coherent tomography and confocal microscopy. Although the impact of these new technologies on survival has not been determined, they offer a wide range of exciting new approaches. In time they may completely revamp the present highly conservative and unsuccessful approaches to early diagnosis.

CpG island hypermethylation and tumor suppressor genes: a booming present, a brighter future

We have come a long way since the first reports of the existence of aberrant DNA methylation in human cancer. Hypermethylation of CpG islands located in the promoter regions of tumor suppressor genes is now firmly established as an important mechanism for gene inactivation. CpG island hypermethylation has been described in almost every tumor type. Many cellular pathways are inactivated by this type of epigenetic lesion: DNA repair (hMLH1, MGMT), cell cycle (p16(INK4a), p15(INK4b), p14(ARF)), apoptosis (DAPK), cell adherence (CDH1, CDH13), detoxification (GSTP1), etc em leader However, we still know little of the mechanisms of aberrant methylation and why certain genes are selected over others. Hypermethylation is not an isolated layer of epigenetic control, but is linked to the other pieces of the puzzle such as methyl-binding proteins, DNA methyltransferases and histone deacetylase, but our understanding of the degree of specificity of these epigenetic layers in the silencing of specific tumor suppressor genes remains incomplete. The explosion of user-friendly technologies has given rise to a rapidly increasing list of hypermethylated genes. Careful functional and genetic studies are necessary to determine which hypermethylation events are truly relevant for human tumorigenesis. The development of CpG island hypermethylation profiles for every form of human tumors has yielded valuable pilot clinical data in monitoring and treating cancer patients based in our knowledge of DNA methylation. Basic and translational will both be needed in the near future to fully understand the mechanisms, roles and uses of CpG island hypermethylation in human cancer. The expectations are high.

DNA methylation analysis: a powerful new tool for lung cancer diagnosis

Carcinoma of the lung is the most common cause of cancer death worldwide. The estimated 5-year survival ranges from 6-16%, depending on the cell type. The best opportunity for improving survival of lung cancer patients is through early detection, when curative surgical resection is possible. Although the subjects at increased risk for developing carcinoma of the lung (long-term smokers) can be identified, only 10-20% of this group will ultimately develop the disease. Screening tests of long-term smokers employed to date (radiography and sputum cytology) have not been successful in reducing lung cancer mortality. The application of molecular markers specific for lung cancer offers new possibilities for early detection. Hypermethylation of CpG islands in the promoter regions of genes is a common phenomenon in lung cancer, as demonstrated by the analysis of the methylation status of over 40 genes from lung cancer tumors, cell lines, patient sputum and/or serum. Determination of the methylation patterns of multiple genes to obtain complex DNA methylation signatures promises to provide a highly sensitive and specific tool for lung cancer diagnosis. When combined with the development of non-invasive methods to detect such signatures, this may provide a viable method to screen subjects at risk for lung cancer.

Detecting rare mutations associated with cancer risk

For more than a decade, investigators have been searching for a means of determining the risk of individuals developing cancer by detecting rare oncogenic mutations. The accumulation of mutations and the clonal evolvement of tumors provide opportunities for monitoring disease development and intervening prior to the presentation of clinical symptoms, or determining the risk of disease relapse during remission. A number of techniques, mostly polymerase chain reaction (PCR)-based, have been developed that enable the detection of rare oncogenic mutations within the range of 10(-2) to 10(-4) wild-type cells. Only a handful of procedures enable the detection of intragenic single base mutations at one mutant in 10-6 or better. These ultra-sensitive mutation detection techniques have produced some interesting results regarding single base mutation spectra and frequencies in p53, Harvey-ras, N-ras, and other reporter genes and DNA sequences in human tissues. Although there is evidence that some individuals may harbor cells or clones expressing genomic instability, the connection with the processes of carcinogenesis is still tenuous. There remains a need for rigorous epidemiological studies employing these ultra-sensitive mutation detection procedures. Since genomic instability is considered key to tumor development, the relevance of the detection of hypermutable clones in individuals is discussed in the context of cancer risk.

Molecular pathogenesis of lung cancer

Lung cancer is the most common cause of cancer death in the United States, killing more than 156,000 people every year. In the past two decades, significant progress has been made in understanding the molecular and cellular pathogenesis of lung cancer. Abnormalities of proto-oncogenes, genetic and epigenetic changes of tumor suppressor genes, the role of angiogenesis in the multistage development of lung cancer, as well as detection of molecular abnormalities in preinvasive respiratory lesions, have recently come into focus. Efforts are ongoing to translate these findings into new clinical strategies for risk assessment, chemoprevention, early diagnosis, treatment selection, and prognosis and to provide new targets and methods of treatment for lung cancer patients. All these strategies should aid in reducing the number of newly diagnosed lung cancer cases and in increasing the survival and quality of life of patients with lung cancer.

Molecular assessment of lymph nodes in patients with resected stage I non-small cell lung cancer: preliminary results of a prospective study

OBJECTIVES

Routine histologic examination of resected lymph nodes in patients with stage I non-small cell lung cancer may underestimate the incidence of advanced disease. The presence of occult lymph node metastases may predict a higher risk of recurrence after intended curative resection. The purpose of this study was to determine the prognostic significance of TP53 and K-ras mutations in histologically determined negative lymph nodes from patients with stage I non-small cell lung cancer who underwent intended curative surgical resection.

METHODS

Between July 1995 and March 1998, clinical data and tissue samples of primary tumors and lymph nodes were collected in a prospective fashion from 102 patients undergoing resection for non-small cell lung cancer (stage I, n = 55; stage II, n = 32; stage IIIA, n = 15). TP53 and K-ras mutations were detected by direct sequencing. If molecular alterations were found in the primary tumor, the corresponding lymph nodes were examined for these same TP53 (by oligonucleotide hybridization) and K-ras (by allele-specific ligation) mutations.

RESULTS

TP53 mutations were found in 47 of 94 primary tumors (50%), and K-ras mutations were present in 26 of 55 adenocarcinomas (47%). A total of 134 lymph nodes from 32 patients with stage I disease were analyzed. In 9 cases (28%) the same TP53 or K-ras mutations were found in tumor and lymph node specimens, suggesting occult metastasis. On the basis of nodal location, 7 patients had their disease upstaged by a single stage and 2 patients by two stages. All 28 patients with stage II or III disease had pathologically determined positive nodes that were confirmed as positive by molecular analysis. Standard histopathologic assessment of regional lymph nodes failed to detect metastases at levels below 0.9% tumor-specific mutant TP53 clones per node. No statistically significant difference in disease-specific or overall survival was observed between patients with stage I disease with and without molecular lymph node metastases.

CONCLUSIONS

Occult lymph node metastases are present in a significant percentage of patients with stage I non-small cell lung cancer. These data suggest that molecular analysis allows a more accurate assessment of staging. However, larger studies are needed to determine the clinical role of molecular staging.

Emerging molecular markers of cancer

Alterations in gene sequences, expression levels and protein structure or function have been associated with every type of cancer. These 'molecular markers' can be useful in detecting cancer, determining prognosis and monitoring disease progression or therapeutic response. But what is the best way to identify molecular markers and can they be easily incorporated into the clinical setting?

Molecular detection of gene mutations and methylation abnormalities: applications in solid tumor diagnosis

As our knowledge of the genetic and epigenetic abnormalities initiating and contributing to tumorigenesis grows, so too does the scope for earlier detection of cancer in patients. This bears an immense potential impact on the clinical management of patients with or at risk of solid tumors, since arguably the greatest problem facing clinicians is late presentation. PCR-based tests have been developed to detect mutant or hypermethylated alleles in exfoliative material and plasma/serum, enabling risk-assessment and early detection programs. Although there are certain limitations, a number of studies have already demonstrated the feasibility and reliability of molecular screening in solid tumors, including colorectal and lung cancers and such molecular approaches may soon be used routinely to detect precursor lesions and early-stage cancer.

Tumor p16M is a possible marker of advanced stage in non-small cell lung cancer

BACKGROUND AND OBJECTIVES

The inactivation of the tumor suppressor gene p16 by methylation (p16M) has been recognized recently as an important process in the oncogenesis for a variety of carcinomas. There have been few reports of its use in lung cancer. We investigate p16M in patients with non-small cell lung cancer (NSCLC).

METHODS

p16M in tumor, plasma, and pleural lavage fluid from patients with resectable NSCLC were investigated by using methylation-specific polymerase chain reaction.

RESULTS

Of the 33 patients studied, 14 (42%) had p16M tumors. There was a significant association between p16M tumors and advanced TNM staging (stage III or IV, P=0.047, Fisher exact test). Circulating p16M was identified in 2 of the 14 patients with p16M tumor and was also associated with advanced TNM staging (P=0.049). The presence of plasma p16M in NSCLC patients and in p16M tumor patients was associated with poor survival and shorter disease-free survival (P=0.0028, P=0.0039, Kaplan-Meier log rank). In addition, p16M was present in three preresectional and four postresectional lavage samples. Preresectional p16M was associated with poor survival and shorter disease-free survival (P=0.0085). p16M tumor involving the visceral pleura was significantly associated with positive p16M postresectional lavage.

CONCLUSIONS

Positive tumor and plasma p16M indicate advanced staging in NSCLC. Patients with plasma and preresection pleural lavage p16M have shorter survival. Further research in this direction is warranted.

Detection of tumor mutations in the presence of excess amounts of normal DNA

Mutations are important markers in the early detection of cancer. Clinical specimens such as bodily fluid samples often contain a small percentage of mutated cells in a large background of normal cells. Thus, assays to detect mutations leading to cancer need to be highly sensitive and specific. In addition, they should be possible to carry out in an automated and high-throughput manner to allow large-scale screening. Here we describe a screening method, termed PPEM (PNA-directed PCR, primer extension, MALDI-TOF), that addresses these needs more effectively than do existing methods. DNA samples are first amplified using peptide nucleic acid (PNA)-directed PCR clamping reactions in which mutated DNA is preferentially enriched. The PCR-amplified DNA fragments are then sequenced through primer extension to generate diagnostic products. Finally, mutations are identified using matrix-assisted laser-desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This method can detect as few as 3 copies of mutant alleles in the presence of a 10,000-fold excess of normal alleles in a robust and specific manner. In addition, the method can be adapted for simultaneous detection of multiple mutations and is amenable to high-throughput automation.

Cancer as an epigenetic disease: DNA methylation and chromatin alterations in human tumours

Cancer is an epigenetic disease at the same level that it can be considered a genetic disease. In fact, epigenetic changes, particularly DNA methylation, are susceptible to change and are excellent candidates to explain how certain environmental factors may increase the risk of cancer. The delicate organization of methylation and chromatin states that regulates the normal cellular homeostasis of gene expression patterns becomes unrecognizable in the cancer cell. The genome of the transformed cell undergoes simultaneously a global genomic hypomethylation and a dense hypermethylation of the CpG islands associated with gene regulatory regions. These dramatic changes may lead to chromosomal instability, activation of endogenous parasitic sequences, loss of imprinting, illegitimate expression, aneuploidy, and mutations, and may contribute to the transcriptional silencing of tumour suppressor genes. The hypermethylation-associated inactivation affects virtually all of the pathways in the cellular network, such as DNA repair (hMLH1, BRCA1, MGMT, em leader), the cell cycle (p16(INK4a), p14(ARF), p15(INK4b), ...), and apoptosis (DAPK, APAF-1, ...). The aberrant CpG island methylation can also be used as a biomarker of malignant cells and as a predictor of their behaviour, and may constitute a good target for future therapies.

Molecular abnormalities in lung carcinogenesis and their potential clinical implications

Development of lung cancer is multistep and requires accumulation of multiple genetic and epigenetic alterations. Modern molecular technology has facilitated a rapid and effective identification of these genetic alterations as well as epigenetic alterations. The determination of molecular alterations in the early tumorigenic process of the lung will not only extend our understanding of the underlying biology but also provide molecular markers for cancer risk assessment, early detection, and molecular classification. In this article, I will discuss the common molecular abnormalities in lung cancer and how these abnormalities may be used as biomarkers in clinical practice.

Gene mutation as a target for early detection in cancer diagnosis

The increasing number of genetic aberrations implicated in the development of human cancer has prompted a search to detect them at the earliest possible stage of their formation. Of the many such genetic changes identified thus far, relatively few meet the standard for markers in early diagnosis and prognosis, namely that the genetic modifications occur during the early onset phase of cancer development. Parallel to the increasing number of such genes is the growing availability of technologies using more powerful and cost-efficient methods that enable mass screening for genetic alterations. The purpose of this review is to summarize the currently available genes that can serve as markers for early detection of cancers and methods that allow their detection.

Quantitation of GSTP1 methylation in non-neoplastic prostatic tissue and organ-confined prostate adenocarcinoma

BACKGROUND

Methylation of regulatory sequences near GSTP1, which encodes the pi class glutathione S-transferase, is the most common epigenetic alteration associated with prostate cancer. We determined whether the quantitation of GSTP1 methylation in histopathologically distinct prostate tissue samples could improve prostate cancer detection.

METHODS

We used a fluorogenic real-time methylation-specific polymerase chain reaction (MSP) assay to analyze cytidine methylation in the GSTP1 promoter in prostate tissue samples from 69 patients with early-stage prostatic adenocarcinoma (28 of whom also had prostatic intraepithelial neoplasia lesions) and 31 patients with benign prostatic hyperplasia. The relative level of methylated GSTP1 DNA in each sample was determined as the ratio of MSP-amplified GSTP1 to MYOD1, a reference gene. We also performed a prospective, blinded investigation to quantitate GSTP1 promoter methylation in sextant prostate biopsy specimens from 21 additional patients with elevated serum prostate-specific antigen levels, 11 of whom had histologically identified adenocarcinoma and 10 of whom had no morphologic evidence of adenocarcinoma. All data were analyzed by using nonparametric two-sided statistical tests.

RESULTS

The median ratios (and interquartile ranges) of MSP-amplified GSTP1 to MYOD1 in resected benign hyperplastic prostatic tissue, intraepithelial neoplasia, and adenocarcinoma were 0 (range, 0-0.1), 1.4 (range, 0- 45.9), and 250.8 (range, 53.5-697.5), respectively; all of these values were statistically significantly different (P< .001). The median ratios of MSP-amplified GSTP1 to MYOD1 in the prospectively collected sextant biopsy samples were 410.6 for the patients with adenocarcinoma and 0.0 for the patients with no evidence of adenocarcinoma (P< .001).

CONCLUSION

Quantitation of GSTP1 methylation accurately discriminates between normal hyperplastic tissue and prostatic carcinoma in small samples of prostate tissue and may augment the standard pathologic/histologic assessment of the prostate.

Genetic heterogeneity in saliva from patients with oral squamous carcinomas: implications in molecular diagnosis and screening

We performed microsatellite analysis at chromosomal regions frequently altered in head and neck squamous carcinoma on matched saliva and tumor samples from 37 patients who had oral squamous carcinoma. The results were correlated with the cytologic findings and traditional clinicopathologic factors to assess the diagnostic and biological potential of these markers. Our data showed that 18 (49%) of the saliva samples and 32 (86%) of the tumors had loss of heterozygosity (LOH) in at least one of the 25 markers studied. In saliva, the combination of markers D3S1234, D9S156, and D17S799 identified 13 (72.2%) of the 18 patients with LOH in saliva (P < 0.001). For tumors, markers D3S1234, D8S254, and D9S171 together identified 27 (84.3%) of the 32 tumors with LOH at any of the loci tested (P < 0.001). Eleven (55%) of the 20 saliva samples with cytologic atypia and seven (35%) of the 17 specimens without atypia had LOH. Significant correlation between LOH in tumor at certain markers and smoking and alcohol use was found. Our results indicate that: 1) epithelial cells in saliva from patients with head and neck squamous tumorigenesis provide suitable material for genetic analysis; 2) combined application of certain markers improves the detection of genetic alteration in these patients; 3) clonal heterogeneity between saliva and matching tumor supports genetic instability of the mucosal field in some of these patients; and 4) LOH at certain chromosomal loci appears to be associated with smoking and alcohol consumption.

Loss of chromosome arms 3p and 9p and inactivation of P16 (INK4a) in normal epithelium of patients with primary lung cancer

The accumulation of genetic alterations in the respiratory epithelium may give rise to cancer and often is accompanied by a series of histologic alterations over a period of several years. Recent studies have identified some molecular alterations in histologically normal-appearing epithelium among patients with lung cancer. To extend these observations, we investigated clonal genetic alterations by using fluorescence in situ hybridization (FISH) analysis and immunohistochemistry in 69 biopsy samples of histologically normal-appearing bronchial epithelium from 22 patients with or without lung cancer. Thirty-seven biopsy specimens from 13 patients were examined for loss of 3p14, and 48 biopsy specimens from 18 patients were examined for loss at 9p21 by FISH. P16(INK4a) expression was analyzed in 54 biopsy samples from 19 patients. In at least one biopsy specimen from five of the 13 patients with primary lung cancer, FISH or immunohistochemistry detected loss of the 3p14 or 9p21 region. In contrast, no alterations were detected for the same regions in the nine patients without primary lung cancer. Our results support the concept that the normal epithelial surface of large bronchi of patients with lung cancer has molecular changes suggestive of the outgrowth of numerous clonal foci.

Cigarette smoking is strongly associated with mutation of the K-ras gene in patients with primary adenocarcinoma of the lung

BACKGROUND

The majority of lung carcinoma cases occur in current or former smokers. K-ras gene mutations are common in lung adenocarcinoma and have been associated with cigarette smoking, asbestos exposure, and female gender.

METHODS

In the current study, the authors examined the contribution of cigarette smoking to K-ras gene mutations in patients with primary lung adenocarcinoma. Smoking histories were obtained from 106 prospectively enrolled patients with primary adenocarcinoma of the lung.

RESULTS

K-ras mutations were detected in the primary tumor using an allele-specific ligation assay. Ninety-two of the 106 patients (87%) with lung adenocarcinoma were smokers. Nonsmokers with this tumor were more likely to be women (11 of 14; 79%), whereas the majority of smokers (57%) were men. K-ras mutations were detected in 40 of 106 tumors (38%) and were significantly more common in smokers compared with nonsmokers (43% vs. 0%; P = 0.001).

CONCLUSIONS

The results of the current study confirm and extend previous observations that smokers with adenocarcinoma of the lung are more likely to have K-ras mutant tumors compared with nonsmokers. The strong link between cigarette smoking and K-ras mutations in adenocarcinoma of the lung supports the role of specific tobacco carcinogens in the etiology of this malignancy.

Selective 'stencil'-aided pre-PCR cleavage of wild-type sequences as a novel approach to detection of mutant K-RAS

The enriched PCR widely used for detection of mutant K-RAS in either tumor tissues or circulating DNA was modified so that abundant wild-type K-RAS alleles are cleaved prior to PCR. We took advantage of an AluI recognition site located immediately upstream of the K-RAS codon 12. The site was reconstituted upon DNA denaturation followed by annealing with a 'stencil', a 16-bp synthetic oligonucleotide complementary to the wild-type sequence. As opposed to normal K-RAS, the mutant allele forms, upon annealing with the stencil, a mismatch at the codon 12 which lies within the AluI enzyme binding site and partially inhibits its activity. The mismatch also lowers the melting temperature of the stencil-mutant K-RAS double helix as compared to stencil-wild-type duplex, so that only the latter is double stranded and selectively digested by AluI at elevated temperatures. The proposed method of stencil-aided mutation analysis (SAMA) based on selective pre-PCR elimination of wild-type sequences can be highly advantageous for detection of mutant K-RAS due to: (i) an enhanced sensitivity because of reduced competition with a great excess of normal K-RAS, and (ii) a decrease in a number of false-positive results from Taq polymerase errors. Application of SAMA for generalized detection of DNA mutations is discussed.

Mitochondrial mutations in early stage prostate cancer and bodily fluids

We recently demonstrated the existence of specific patterns of somatic mitochondrial DNA (mtDNA) mutations in several cancers. Here we sought to identify the presence of mtDNA mutations in prostate cancer and their paired PIN lesions. The D-loop region, 16S rRNA, and the NADH subunits of complex I were sequenced to identify mtDNA mutations in 16 matched PIN lesions and primary prostate cancers. Twenty mtDNA mutations were detected in the tumor tissue of three patients. Identical mutations were also identified in the PIN lesion from one patient. This patient with multiple point mutations also harbored a high frequency of microsatellite instability (MSI-H) in nuclear mononucleotide repeat markers. Remarkably, identical mutations were also detected in all (3/3) matched urine and plasma samples obtained from these patients. Although mitochondrial mutations are less common in prostate adenocarcinoma, they occur early in cancer progression and they can be detected in bodily fluids of early stage disease patients. The identification of MtDNA mutations may complement other early detection approaches for prostate cancer.

Technical aspects of minimal residual disease detection in carcinoma patients

The burden of occult malignant cells which remains after a course of treatment that has resulted in clinical remission is referred to as minimal residual disease (MRD). MRD is increasingly considered as a determinant of local or systemic recurrence in cancer patients. During the last 20 years, methods for the detection of rare cancer cells have evolved from mere cytomorphological investigations to a variety of immunological and molecular assays. Since surgical therapy remains the best treatment option for cancer patients with resectable tumors, the first question to address is whether the removal of the tumor was complete or some cancer cells remained from the tumor at the primary site. Several tumor-associated DNA alterations have been identified to solve this diagnostic problem. Assays detecting tumor-associated DNA alterations have been applied to resection margins and body fluids such as bronchoalveolar lavage, sputum, urine, pancreatic juice, colonic lavage, and stool. Due to the higher sensitivity of immunocytochemical and reverse-transcriptase polymerase chain reaction (RT-PCR)-based assays, the second question to be addressed is whether systemic hematogenous or lymphatic spread of cancer cells occurred. Disseminated cancer cells have been detected in bone marrow aspirates, peripheral blood, and lymph node biopsies, and cancer cell dissemination is regarded as a relevant and independent prognostic factor. Thus, sensitive techniques for the detection of MRD are likely to guide indications for surgical or adjuvant therapy protocols in clinical oncology. However, since many of the assays for the detection of MRD are complex, and results are influenced by a variety of technical aspects, the majority of diagnostic applications have not yet been sufficiently standardized. Consequently, quality control and reproducibility of minimal disease detection assays remain unsolved problems. Therefore, well controlled collaborative studies are urgently required to evaluate indications and diagnostic standards for these assays. This review summarizes technical aspects and their implications for the clinical application of presently available assays for MRD detection in carcinoma patients.

Molecular characterization of minimal residual cancer cells in patients with solid tumors

The failure to reduce the mortality of patients with solid tumors is mainly a result of the early dissemination of cancer cells to secondary sites, which is usually missed by conventional diagnostic procedures used for tumor staging. PCR was shown to be superior to conventional techniques in detecting circulating tumor cells and micrometastases allowing the identification of one tumor cell in up to 10(7) normal cells in various sources such as blood, bone marrow, lymph nodes, urine or stool. The methods used are based on the detection of either genomic alterations in oncogenes and tumor suppressor genes or on the mRNA expression of tissue-specific and tumor-associated genes. The additional implementation of techniques for cancer cell purification had a significant impact on analytical sensitivity and specificity of MRCC detection. For patients with e.g. melanoma, breast, colorectal or prostate cancer it was demonstrated that the presence of disseminated cancer cells defines a subgroup of patients with reduced time to recurrence. The possibility to use easily accessible body fluids as a source for MRCC detection enables longitudinal observations of the disease. In this review we discuss the potential of molecular characterization of MRCC as a tool to improve prognostication, therapy selection and drug targeting as well as therapy monitoring.

Epigenetic lesions causing genetic lesions in human cancer: promoter hypermethylation of DNA repair genes

The existence of genetic alterations affecting genes involved in cellular proliferation and death, such as TP53 and K-ras, is one of the most common features of tumour cells. Recently, gene inactivation by promoter hypermethylation has been demonstrated. Methylation is the main epigenetic modification in mammals and abnormal methylation of the CpG islands located in the promoter region of the genes leads to transcriptional silencing. Examples include the p16INK4a, p15INK4B, p14ARF, Von Hippel-Lindau (VHL), the oestrogen and progesterone receptors, E-cadherin, death associated protein (DAP) kinase and the first tumour suppressor gene described, retinoblastoma (Rb) gene. In most cases, methylation involves loss of expression, absence of a coding mutation and restoration of transcription by the use of demethylating agents. However, is there a linkage between genetic and epigenetic alterations? Our results show one side of this puzzle demonstrating that epigenetic lesions drive genetic lesions in cancer. Four specific epigenetic lesions, promoter hypermethylation of the DNA mismatch repair gene hMLH1, the DNA alkyl-repair gene O(6)-methylguanine-DNA methyltransferase (MGMT), the detoxifier glutathione S-transferase P1 (GSTP1) and the familial breast cancer gene BRCA1 may lead to four specific genetic lesions, microsatellite instability, G to A transitions, steroid-related adducts and double-strand breaks in DNA. This is probably only the beginning of an extensive list of epigenetic events that change and make the genetic environment of the transformed cell unstable.

K-ras Point Mutation Detection in Lung Cancer: Comparison of Two Approaches to Somatic Mutation Detection Using ARMS Allele-specific Amplification

Background: The use of sensitive molecular techniques to detect rare cells in a population is of increasing interest to the molecular pathologist, but detection limits often are poorly defined in any given molecular assay. We combined the approaches of real-time quantitative PCR with ARMSTM allele-specific amplification in a novel assay for detecting mutant K-ras sequences in clinical samples.

Methods: ARMS reactions were used to detect seven commonly occurring mutations in the K-ras oncogene. These mutations produce amino acid changes in codon 12 (Gly to Ala, Arg, Asp, Cys, Ser, or Val) and codon 13 (Gly to Asp). A control reaction was used to measure the total amount of amplifiable K-ras sequence in a sample so that the ratio of mutant to wild-type sequence could be measured. Quantitative data were confirmed for a selection of samples by an independent cloning and sequencing method. The assay was used to analyze 82 lung tumor DNA samples.

Results: The assay detected K-ras mutations in 44% of adenocarcinomas, which is equivalent to frequencies reported in the literature using ultrasensitive techniques. Forty-six percent of squamous carcinomas were also positive. The ratio of mutant sequence in the tumor DNA samples was 0.04–100%.

Conclusions: The assay is homogeneous, with addition of tumor DNA sample being the only step before results are generated. The quantitative nature of the assay can potentially be used to define the analytical sensitivity necessary for any specified diagnostic application of K-ras (or other) point mutation detection.

Differential frequencies of p16(INK4a) promoter hypermethylation, p53 mutation, and K-ras mutation in exfoliative material mark the development of lung cancer in symptomatic chronic smokers

PURPOSE

The aim of this study was to investigate the frequency of three (epi)genetic alterations (p53 and K-ras mutations and p16(INK4a) promoter hypermethylation) in symptomatic chronic smokers compared with patients with lung cancer and to evaluate the use of exfoliative material for such analyses.

PATIENTS AND METHODS

Fifty-one patients with histologically confirmed lung cancer and 25 chronic smokers (> 20 pack-years) were investigated for mutations in the K-ras (codon 12) and p53 (codons 248, 249, and 273) genes and for allelic hypermethylation of the p16(INK4a) gene. DNA was isolated from sputum and bilateral bronchial lavage, and brushings were taken at bronchoscopy.

RESULTS

Forty-one genetic lesions were detected within exfoliative material from the group of 51 patients with lung cancer and 10 lesions in the chronic smoker group. K-ras mutations occurred exclusively in the lung cancer group, whereas p53 mutations and p16(INK4a) promoter hypermethylation were also found in chronic smokers. Three of eight chronic smokers who harbored an (epi)genetic alteration were subsequently diagnosed with lung cancer. Analysis of sputum yielded information equivalent to that of samples obtained during bronchoscopy.

CONCLUSION

p16(INK4a) promoter hypermethylation and p53 mutations can occur in chronic smokers before any clinical evidence of neoplasia and may be indicative of an increased risk of developing lung cancer or of early disease. K-ras mutations occur exclusively in the presence of clinically detectable neoplastic transformation. Molecular analysis of sputum for such markers may provide an effective means of screening chronic smokers to enable earlier detection and therapeutic intervention of lung cancer.

Genetic changes in solid tumors

Although most solid tumors are treated surgically, determining the genetic changes present in the tumor of an individual patient is becoming increasingly important for managing the oncology patient. Our knowledge of the genetic alterations that characterize and predispose to solid tumors continues to expand. Concurrently, the advent of newer technologies such as DNA chips has the potential to enable a more rapid and comprehensive assessment of these changes. The ultimate goal of this new information and technology is to provide sensitive and specific tests that reduce unnecessary procedures and optimize therapy. This review addresses the utility of molecular testing in evaluating cancer. A review of the current technology and hereditary cancer syndromes is also presented.

Detection of microsatellite alterations in the DNA isolated from tumor cells and from plasma DNA of patients with lung cancer

In this paper, we show that the same panel of three microsatellite markers is useful for the detection of alterations in the DNA of tumor cells and plasma from patients diagnosed with SCLC and NSCLC. In 31% of the SCLC patients, we detected a microsatellite alteration(s) or LOH in at least one locus. In the group of patients diagnosed with NSCLC, a microsatellite alteration or LOH was detected in at least one locus in 33% of the patients. In all but 2 patients, the identical alteration observed in the DNA from tumor cells was also detected in the DNA isolated from blood plasma. This work confirms the results described by other groups and it extends the diagnostic possibilities of finding tumor cell-specific DNA alterations also in the DNA freely circulating in plasma and serum of patients with cancer.

Facile detection of mitochondrial DNA mutations in tumors and bodily fluids

Examination of human bladder, head and neck, and lung primary tumors revealed a high frequency of mitochondrial DNA (mtDNA) mutations. The majority of these somatic mutations were homoplasmic in nature, indicating that the mutant mtDNA became dominant in tumor cells. The mutated mtDNA was readily detectable in paired bodily fluids from each type of cancer and was 19 to 220 times as abundant as mutated nuclear p53 DNA. By virtue of their clonal nature and high copy number, mitochondrial mutations may provide a powerful molecular marker for noninvasive detection of cancer.