Genes Offer Researchers a “Crystal Ball” to Help Them Prevent, Diagnose, and Treat Cancer
November 12, 2006
BOSTON - The science of cancer prevention has advanced to the point where researchers now say they can detect "cancer genes" in the breath of smokers, and can test the presence of two proteins in men they say will predict development of prostate cancer a decade in advance. All of these novel findings need much more examination, of course, but scientists at the American Association for Cancer Research's Frontiers in Cancer Prevention Research meeting, say these examples illustrate how it is becoming increasingly possible to use genes and their protein products to help predict and diagnose cancer, as well as choose therapy that offers the most potential for a good result. These researchers will also discuss a test that can pick out patients who have pancreatic cancer - an advance that offers hope the disease can be treated at earlier stages than it is now - and how several unique genes can predict which prostate cancer or lung cancer patients will develop aggressive tumors that need additional treatment. Cancer is a disease of genes, they say, so genes can be employed as a crystal ball to thwart the disease.
Lung carcinogenesis tracked by DNA methylation mapping in exhaled breath
For the first time, researchers have demonstrated that it is possible to detect DNA methylation in the breath of smokers and lung cancer patients, suggesting that, in theory, it may be possible to use this technique to identify people who have undiagnosed lung cancer or are at high risk of developing the disease.
Investigators at the Wadsworth Center, the public health laboratory of the New York State Department of Health, have been able to develop an assay that simultaneously detects the presence of methylation in six tumor suppressor genes - a process by which a gene is chemically silenced. The assay examines the promoter region of a gene, where certain cytosine nucleotide bases may be methylated, preventing the gene from being expressed.
The seven participants tested so far breathe for ten minutes into a commercially available handheld device, which cools the air, forming a condensed vapor, to which the methylation assay is applied. Investigators found it could detect the presence of the methylated form in all six tumor suppressor genes. For RASSF1A, the test was negative in non-smokers, and positive in both current and ex-smokers. For DAPK, methylation was more variable, given smoking status. The four other tested genes (p16, MGMT, PAX5B,CDH1) known to be methylated in various stages of lung cancer development, were minimally or not methylated, in this pilot study of predominantly cancer-free smokers.
"Dr. Weiguo Han and I have shown that this approach is technically feasible, and if further research demonstrates the assay can measure DNA in such a way that it diagnoses or predicts lung cancer, this could be important for non-invasive lung cancer testing," said the study's lead author, Simon D. Spivack, M.D., M.P.H., a research physician at the Wadsworth Center, and a specialist in lung diseases. "But we are a long way from that point." Han, a post-doctoral fellow in Spivacks' laboratory and the study's first author, will be presenting the findings.
Spivack said his study was only the third to date that proved DNA could be tested in condensed breath - German researchers reported the first such result in 2003, followed by an Italian group in 2005 - and the first to find methylation-silenced tumor suppressor genes in the breath of patients at risk or harboring lung cancer.
"The concept of testing exhaled breath is not new - that's what breathalyzers do when they measure small volatile molecules such as alcohol, as well as inflammation molecules that are currently being assayed to test the activity of asthma and other lung diseases," said Spivack. "But what is rather remarkable here is that DNA can be tested in the air that comes from the lungs and airways, and that it might be possible to use this in diagnosis of lung cancer in particular, and gene-dysregulation disorders of the lung, in general."
The DNA is believed to be released when cells turn over, or are damaged, in the lungs and airways, he said. "Although it is not possible to say at this point the precise anatomic origin of the airway-derived DNA being tested, it may be that different patterns of gene methylation will themselves actually map the origin of this DNA to particular regions of the airway," Spivack said.
"Our goal is early detection of lung cancer and risk stratification," he said. "If all we can do is confirm that a smoker is smoking, or that a lung cancer patient has cancer, then this test will be meaningless. But we now know it is technically feasible to measure DNA methylation in breath."
Multiplexed serum markers screening for detection of pancreatic cancer
A panel of 10 blood biomarkers performed almost perfectly in picking out people who had pancreatic cancer from those who didn't, according to researchers at the University of Pittsburgh. The advance raises hopes that a test can be developed to screen for the aggressive cancer in time to treat it, they say.
"Early detection of pancreatic cancer is crucial to survival, but there has been no way to diagnose it early before symptoms occur," said the lead investigator, Anna E. Lokshin, Ph.D., an associate professor of medicine and pathology at the University of Pittsburgh School of Medicine. "This assay represents a new way to screen for disease that appears to be applicable to pancreatic cancer, and potentially, to other cancer types."
The assay contains the largest panel of blood-based biomarkers to be examined simultaneously in pancreatic cancer. It consists of proteins known to be secreted by pancreatic tumors as well as proteins that represent the body's response to that tumor growth, Lokshin said.
"Tumors are located in the context of certain tissues, and those tissues react in their own individual ways to the cancer," she said. "For example, tissue-specific proteins try to fight the cancer, and each tumor type grows blood vessels in tissue uniquely, so we believe the body responds differently to each kind of cancer."
The researchers initially evaluated a panel of 44 protein biomarkers, including cytokines, chemokines, adhesion molecules and hormones, and used blood from 100 pancreatic cancer patients and a control group of 400 healthy people to find those associated with the cancer. They used a microbead array, which can sample up to 100 different proteins simultaneously, and found 10 biomarkers that offered the highest diagnostic power, Lokshin said. Two of those biomarkers are CA125, which can detect a number of cancers but which is not very specific, and CA19-9, which has been known to correlate weakly with pancreatic cancer.
They found that this panel of markers correctly identified pancreatic cancers 97 percent of the time, with a sensitivity of 95 percent (meaning it could correctly identify cancerous lesions) and with a 98 percent specificity (the ability to detect truly negative cases).
The researchers are continuing to study, validate, and perfect the assay, and test its ability to identify pancreatic cancer at early, treatable stages. Although pancreatic cancer is relatively rare, survival is poor compared to most other forms of cancer - it is the fourth leading cause of cancer-related deaths in males and the fifth-leading cause of cancer-related deaths in females.
A diagnostic screen for pancreatic cancer would likely first be used in smokers, because use of tobacco is a known risk factor for developing pancreatic cancer, Lokshin said.
The researchers also are developing similar assays for ovarian, breast, lung, endometrial, head and neck, and esophageal cancers. "So far, every panel is different for each cancer to the point where we can say with greater than 97 percent certainty which cancer it is," she said.
"Surprisingly, although in theory body response could be similar for several cancers, in practice it is very different."
TMPRSS2-ERG fusion prostate cancer: an early molecular event associated with invasion
The presence of a gene fusion in prostate tumors is significantly associated with aggressive cancer, metastatic spread, and an increased probability of death, a team of researchers is reporting. They say that the new gene, formed by the fusion of TMPRSS2 and ERG, may serve as a biomarker to separate patients who might benefit from radical prostate cancer therapy from those who potentially need little, if any, treatment.
"We believe this gene has the potential to be used as a diagnostic and prognostic test, which could offer thousands of patients peace of mind and spare them from unnecessary surgery and therapy," said the study's lead author, Sven Perner, M.D., a postdoctoral fellow in the Department of Pathology at Harvard University's Brigham and Women's Hospital in Boston. He worked with researchers from the Universities of California and Michigan, Johns Hopkins University and McGill University in Montreal.
Perner and his colleagues reported the discovery of the fused gene last year and they now say that TMPRSS2-ERG occurs in about 50 percent of prostate cancers - making it the most common genetic aberration in human cancer, and the first one found in a common solid cancer. Fused genes and chromosomal rearrangements have been found in several blood cancers, such as chronic myelogenous leukemia (CML) and in soft tissue tumors, such as Ewing's sarcoma, but these diseases are rare compared to prostate cancer, which is one of the leading cancers among American men.
In this study, the researchers sought to learn whether TMPRSS2-ERG is associated with a particular prostate cancer stage, and how it might be contributing to development of the cancer. They gathered 406 prostate tissue samples, representing a range of benign, precursor, and malignant prostate lesions, and used a FISH analysis to look for TMPRSS2-ERG. They didn't find any evidence of the fused gene in non-cancerous samples, but found it was present in 48.5 percent of localized prostate cancer tumors, 30 percent of hormone-naïve metastases, and in 33 percent of hormone refractory metastasis, as well as in about 20 percent of prostatic intraepithelial neoplasias, a lesion believed to be precursor of invasive prostate cancer.
The investigators also discovered that the gene fusion could occur in two different ways. The genes, TMPRSS2, which is regulated by the male sex-hormone androgen, and ERG, which is a potential oncogene, are located close to one another on chromosome 21. When fused, TMPRSS2 drives over-expression of the ERG gene. According to Perner, fusion can occur when the piece of DNA separating the genes breaks off and the genes merge (a process described as "fusion through deletion"), or if parts of each gene break off and switch positions ("translocation").
They found that TMPRSS2-ERG fusion through deletion was more common in the tumor samples as compared to TMPRSS2-ERG fusion through translocation. More recent work has found a significant association between TMPRSS2-ERG fusion and death from prostate cancer, although the researchers have not yet been able to determine which fusion form predicted the highest risk of death.
Perner says investigators are hoping to find a small molecule to inhibit the TMPRSS2-ERG fusion protein in the same way that the drug Gleevec has revolutionized care of CML.
Prediagnostic interleukin-6, C-reactive protein and prostate cancer incidence and mortality
Increased levels of two markers of inflammation, interleukin-6 (IL-6) and C-reactive protein (CRP), are significantly associated with prostate cancer incidence and mortality almost a decade prior to diagnosis, say researchers at the Harvard School of Public Health.
They also found that elevated CRP in these men was associated with a two-fold increased risk of developing fatal prostate cancer, compared to men with the lowest levels of the protein.
"The results of this study provide further evidence that inflammation is involved in development and progression of prostate cancer," said the study's lead author, Jennifer Rider Stark, a graduate student in epidemiology.
Stark said that IL-6 and CRP were more strongly associated with prostate cancer risk and death from prostate cancer in normal weight men. Because IL-6 is secreted from adipose (fat) tissue, levels of the cytokine are naturally higher in overweight or obese men. "It is possible that high levels of IL-6 and CRP in men with a healthy body weight may be more indicative of a pro-inflammatory environment in the prostate," she said.
Some studies have already shown that high levels of IL-6 and CRP can be associated with a poor prognosis in prostate cancer patients, but this is one of only a few studies to examine whether these markers can predict risk before symptoms develop and cancer is diagnosed.
The findings come from a prospective study nested within the Physician's Health Study, and included 516 men who later developed prostate cancer and 516 matched controls who did not. The researchers examined blood taken from each participant early in the study - a median of 9.4 years before prostate cancer was diagnosed in the cases. Levels of IL-6 and CRP were compared among men who did and did not go on to develop cancer. Long-term follow-up of the cases also allowed the researchers to assess the effect of these markers on prostate cancer mortality.
They found that high levels of CRP in the blood was associated with a higher incidence of prostate cancer development among all patients and associated with a two-fold increased risk of developing lethal prostate cancer. IL-6 levels were not associated with prostate cancer risk overall. But when they separated out men by body mass index, those who had a healthy weight and high IL-6 in their blood had a 40 percent higher risk of developing prostate cancer.
Researchers suspect that abnormal amounts of IL-6 and CRP are markers of biological processes involved in development of a number of diseases, including cancer. IL-6 is secreted by immune cells in response to infection or trauma, and it, in turn, stimulates synthesis of CRP in the liver, which is believed to play a role in response to infections and cellular damage control. CRP has been found to be a marker of cardiovascular disease, diabetes and colon cancer, but its use as a cardiology screening test has been controversial.
Stark noted that the predictive power of these two markers for determining prostate cancer risk and mortality needs to be confirmed in other prospective studies. She added, "Understanding the role of inflammation in prostate cancer is important because inflammatory pathways could potentially be targeted for prevention and treatment."
Characteristics of long-term lung cancer survivors
In preliminary findings from an ongoing study, researchers at Mayo Clinic have identified four different factors they say predicts long-term survival in patients diagnosed with lung cancer, and one of the strongest is inheritance of a gene variant, GSTM1 positive, which is more efficient than another allele type of the GSTM1 gene at detoxifying carcinogens.
They found that patients with a null type at this gene were four times more likely to die within two years as were matched patients who had the positive variant.
The researchers also found that patients who had surgery, who were active, and whose cancer did not come back or progress were much more likely to survive five years or longer.
"Outcome varies among lung cancer patients, even within groups that have the same stage at the time of diagnosis, and so it is difficult to know how aggressively to treat and provide follow-up care for individual patients," said the study's lead investigator, Ping Yang, M.D., Ph.D., a clinical and genetic epidemiologist at Mayo Clinic.
"In order to enhance both survival and quality of life, we are trying to establish a model that will identify patients who would benefit from additional clinical intervention, and the data we have accumulated to date could be enormously helpful," she said.
To derive these predictive factors, the researchers aim to compare 400 lung-cancer patients treated at Mayo Clinic and who have survived five or more years, with 400 patients who lived less than two years after treatment. The researchers match the groups by age at diagnosis, gender, tumor cell type, cancer stage and the number of primary lung cancers, and they examine blood samples and follow the progress of the patients' disease as well as their quality of life.
In an interim analysis of data on 150 patients in each group, the researchers specifically found that patients who experienced any progression or recurrence of their cancer were almost three times more likely to die within two years, compared to patients of the same cancer stage whose disease did not progress or return.
They also concluded that lung cancer patients who had surgery were three times as likely to have longer survival as matched patients who did not have surgery. "This can be very useful information for patients who are undecided about whether they should risk having surgery," she said.
Patients who reported being "unable to do work or could only do light work" were at a 2.7-5.8 fold higher probability of dying within two years than were patients who were active, the researchers also discovered. "The clinical care of these patients is a long- term process," Yang said. "If, through follow-up and monitoring, we find a patient is physically inactive, we may recommend exercise and rehabilitation as appropriate to keep them stronger."
Knowing the contribution of inheriting a GSTM1 gene form to outcome is also important, she said. "If our model tells us that a patient's cancer has a higher chance of recurring or progressing because of innate genetics in metabolism, we can watch them more closely, and consider treating them aggressively and promoting preventive measures," Yang said.
The GSTM1 gene is just one of many candidate genes the investigators are studying in these patients.
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The mission of the American Association for Cancer Research is to prevent and cure cancer. Founded in 1907, AACR is the world's oldest and largest professional organization dedicated to advancing cancer research. The membership includes more than 24,000 basic, translational, and clinical researchers; health care professionals; and cancer survivors and advocates in the United States and more than 70 other countries. AACR marshals the full spectrum of expertise from the cancer community to accelerate progress in the prevention, diagnosis and treatment of cancer through high-quality scientific and educational programs. It funds innovative, meritorious research grants. The AACR Annual Meeting attracts over 17,000 participants who share the latest discoveries and developments in the field. Special Conferences throughout the year present novel data across a wide variety of topics in cancer research, diagnosis and treatment. AACR publishes five major peer-reviewed journals: Cancer Research; Clinical Cancer Research; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Epidemiology, Biomarkers & Prevention. Its most recent publication, CR, is a magazine for cancer survivors, patient advocates, their families, physicians, and scientists. It provides a forum for sharing essential, evidence-based information and perspectives on progress in cancer research, survivorship and advocacy.
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