Vol. 14 •Issue 6 • Page 52
The Potential Shift in Cancer Diagnostics
Spurred by recent biological and technological advances such as the Human Genome Project, array analysis and laser capture microdissection, the essence of cancer diagnostics appears to be on the verge of a major transformation.
Despite unrelenting research efforts in the diagnosis and treatment of cancer, the capricious disease remains one of the leading causes of death in the United States and across the globe. Second only to heart failure, cancer is a leading cause of death among Americans, as it is responsible for one of every four deaths in the United States.1 About 16 million new cancer cases have been diagnosed since 1990, and it is estimated that more than 1.2 million new cases have been diagnosed in 2002 alone.1
When a person is diagnosed with cancer, there is a desperate search for answers to some very specific questions. The patient will ask, “What are my options? What kinds of therapy or treatment will I need?” And most importantly, “What are my chances of surviving this?” These are all questions that patients expect to be answered in the prognosis.
But prognosis is defined as a prediction of the future course and outcome of a disease, and an indication of the likelihood of recovery from that disease.2 It is the physician’s attempt to project what is likely to happen to an individual patient. Currently, prognosis for cancer patients is about prediction. And although it is a prediction based on many factors such as the type, stage and grade of the cancer, it is a prediction nonetheless. But what if a prognosis could be much more precise than mere prediction?
Scientists at most major cancer treatment centers are diligently working on gene and protein patterns for the early detection of cancer. In addition to more accurate means of diagnosis, these patterns are expected to lead to distinct, accurate prognoses and tailored therapies and treatments individualized for each cancer patient. As new diagnostic techniques result in finer distinctions of the nature of the cancers that are found, laboratorians can expect to take on an even greater role in determining the specific prognosis and the best treatment or therapy for a particular patient.
The Way It Is
Today, the pathologist’s task is quite traditional, according to many experts. Determining which tumor a patient has is done primarily by histopathology–H and E sections, with some special staining being used. This certainly appears to be a sufficient method for diagnosis of most cancers, says Sheila E. Taube, PhD, associate director, cancer diagnosis program, division of cancer treatment and diagnosis, National Cancer Institute (NCI).
“Well over 90 percent of tumors can be identified as being a tumor and from what organ based on classical histopathology,” she says.
As for classification in terms of establishing a prognosis for the tumor, a number of organizations have come up with characteristics of tumors and tumor classification schemes in which they identify issues or characteristics such as grade and lymph node status. This provides some sense of the projected behavior of the tumor.
“For the vast majority of tumors these days, that is probably the way the diagnosis is made,” says Dr. Taube.
There are criteria that pathologists and physicians start with—the tumor, nodes, metastases (TNM) staging—which are not at all based on molecules. It is all basic anatomy of the tumor. And even the additional criteria that are frequently added to that like tumor grade, for instance, does not involve measuring molecules. The pathologist simply looks at the tumor tissue under a microscope and grades it based on characteristics such as the dividing of cells and abnormalities of the nuclei, say experts.
The Problems of Today
As effective as the current method of cancer diagnostics may be, it is not without flaw. At “Lab 2005: Your Path to the Future,” an AACC-sponsored conference held in New York, Eleftherios P. Diamandis, MD, PhD, FRCP, head, section of clinical biochemistry, department of pathology and laboratory medicine, Mount Sinai Hospital, addressed some of the problems with current cancer diagnostics. Regarding morphology, Dr. Diamandis suggests that one of the greatest problems is subjectivity of analysis.
“Two pathologists who classify a tumor would never come up with the same classification because the analysis is indeed subjective and there is variation between observers,” he explains. “We classify tumors into various groups and we know that these groups are heterogeneous because some people respond very well, some people die very quickly, some people respond to some treatments and some people do not.”
In studying the morphology of the tumor, scientists record what they see, but this does not necessarily reveal the underlying biology of the tumor. These are two different things, according to Dr. Diamandis, who maintains that people who are classified in the same category based upon pathological criteria will not necessarily have the same clinical course.
“The problem is the cases of what we are doing with immunohistochemistry during this morphological analysis,” he contends. “We are usually only looking at one molecule at a time.”
There are also limitations of the current markers in predicting therapeutic response and prognosis. They are mainly used for monitoring therapy of cancer patients, but outside of that, they are not very good, claims Dr. Diamandis.
The conclusion that many experts are coming to is that although medical professionals are doing well with what they have at the moment, the current methods will probably not lead to the next level of cancer diagnostics.
“Current laboratory diagnostics are probably sufficient to get us to first base, but they are not sufficient to get us a homerun,” says Dr. Taube. “Therefore, we need more help in making better treatment decisions.”
As tumors are being identified at much earlier stages, it becomes less clear how best to treat them. Dr. Taube explains that if a woman has node-negative breast cancer and it is small, the odds are that greater than 90 percent of these women are going to be alive and free of disease at 10 years. But Dr. Taube questions whether it is possible to find the 10 percent or 15 percent of women who will benefit from additional therapy.
“We know that overall, with node negative breast cancer, about 25 percent to 30 percent of women will ultimately die of metastatic disease,” says Dr. Taube. “We can’t find those women reliably now, so recommendations have been made for everybody to consider systemic therapies.”
But the systemic therapies have risks as well. Therefore, health professionals are forced to balance risk of recurrence and death from the disease vs. the risk of side effects of the therapy.
“If we had better diagnostics that could say, ‘You really are at such low risk that you only have a 2 percent or 3 percent chance of ever seeing this disease again,’ we could determine that the patient probably will suffer more from the treatment than from the cancer,” says Dr. Taube.
This need for better diagnostics does not only exist in breast cancer, however. It is significant in other cancers such as prostate and lung cancers. Since cancers are now being detected earlier, clinicians are not sure whether the nature of the tumors that they see early is the same as the tumors that they might see later, experts say. Some cancers may not be growing and proliferating and, therefore, may not require major surgery. To the experts in the field, all of this represents a tremendous need for better, more advanced methods of cancer diagnostics.
“We need more objective and biologically-relevant tumor classification schemes for the purpose of prognosis and selection of therapy. We need better cancer markers for population screening and early diagnosis and, more importantly, for cancer prevention,” insists Dr. Diamandis. “We are now seeing the power that exists in laboratory medicine, and the traditional method that we as pathologists are doing is probably not the best approach that we have.”
The Paradigm Shift
In search of tumor markers, experts like Dr. Diamandis are realizing that there may not be one, single true tumor marker. And experts also point out that when scientists try to do screening or diagnosis with the measurement of just a single tumor marker, it is not usually very successful.
“The shift away from looking at one molecule at a time is motivated by the fact that this approach has been of limited benefit from the standpoint of usefulness in the clinic,” says Tracy G. Lugo, PhD, program director, diagnostics research branch, cancer diagnosis program, NCI. “There are really very few single molecules that are routinely measured because they have proven clinical benefit.”
Estrogen receptor in breast cancer is an example of the single molecules that have, in fact, demonstrated clinical benefit. Scientists are now measuring amplification or over-expression of HER2 because it tells them whether or not a patient is likely to benefit from a particular set of treatments. This is one diagnostic method that uses a single molecule to influence therapy and customize treatment for cancer patients.3
With the exception of HER2 expression, however, experts are hard-pressed to identify more single molecules that bear significant clinical benefit. But now that the technology is available to look at the expression of many genes and proteins at a time, scientist are eager to find out if examining the expression patterns in tumors will answer some of the questions that the traditional methods are not answering.
The New Technology
With all the technological advances over the last 10 years, the paradigm shift in cancer diagnostics appears to be inevitable. According to many experts, the most significant advance facilitating the shift is the Human Genome Project. Other advances that are having a solid impact as well are bioinformatics, the emergence of the array analysis and biological mass spectrometry for large molecules, according to Dr. Diamandis. In addition to these, there is another set of related technologies. These include the emergence of the DNA arrays, protein arrays, tissue arrays and other technology like laser capture microdissection, single nucleotide polymorphisms (SNPs) and comparative genome hybridization.
•DNA/RNA Microarrays
Microarray technology is one of the major technological advances being applied to the study of gene expression. But this is not the only possible application. Scientists are now using them to detect SNPs and do sequence by hybridization, a very high-throughput method, according to Dr. Diamandis. He also claims that they are starting to be used for protein expression studies and identifying protein-protein interactions.
The tissue expression profiles are actually very useful not only for studying gene expression, but for discovering new tumor markers. By systematically examining gene expression studies in various tissues, scientists can isolate and determine which genes are expressing which tissues, then identify tissue-specific expression of certain genes, experts say.
The theory behind microarrays and their benefit in the realm of cancer diagnostics is simple. Scientists believe that because tumor behavior is dictated by the expression of thousands of genes, microarray analysis should allow that behavior and the clinical consequences to be predicted.4
•Tissue Microarrays
Another technology that came about over the last few years is tissue microarrays. This technology allows clinicians to do 500 experiments with one shot, as Dr. Diamandis explains.
“The way it is done is to take the classical paraffin blocks, drill them and pick up small pieces of tissue that you know are cancerous and replant them into another block,” he says. “In this recipient block, you can actually put up to 500 little pieces of tissue and when you make a cut, you have to take 500 pieces at a time and you can microscopically look at them after you stain them. It is a very powerful and high-throughput technique.”
•Protein Microarrays
Experts anticipate that the next breakthrough in microarray analysis will be the protein microarrays, which are not yet developed. But scientists have great hopes that over the next two to three years they will have the ability to measure hundreds or even a thousand proteins at one time by using this kind of microarray technology.
•Comparative Genome Hybridization
Another technique that came about within the last few years is comparative genome hybridization, which allows scientists to examine the whole genome and determine if any genes have deleted or have amplified in their sample of interest. As Dr. Diamandis explains, this technique is done by extracting DNA from a normal tissue and from a cancerous tissue. The normal DNA is labeled with red dye and the cancerous DNA is labeled with green dye. Two chromosomes are then hybridized. The idea is that if one dominates, there is probably a deletion of the cancer.
One major advance in this technique is that it has now been refined to work in an array format. So, instead of hybridizing to chromosomes, which experts say is technically more difficult, clinicians can hybridize to an array, which covers the whole gene.
“It is an extremely powerful technology,” claims Dr. Diamandis. “We actually see what is deleted or amplified within the whole gene.”
•Laser Capture Microdissection
Another important technique that is very young is laser capture microdissection. This technique addresses the major issue that oftentimes an extracted tumor tissue is mostly normal tissue contamination, according to experts. Laser capture microdissection allows clinicians to dissect a very small area that is 100 percent cancerous, and other areas that are 100 percent normal, so that they can make meaningful comparisons.
A special inverted microscope with a tip is placed in the area to microdissect. By using a laser beam, the piece can be cut and extracted with a thermoplastic polymer, explains Dr. Diamandis. This is another essential technique that allows clinicians to work with very well-defined tissue.
•SNPs
SNPs, another major technology, are slight changes in DNA that distinguish one human from the next. There aren’t many distinct genetic variations other than this, experts contend. It is believed that these changes in our genomes are the ones that are predisposing us to different diseases. Scientists now trust that if they have ways of genotyping all the genomes from these SNPs, they may be able to predict who is predisposed to a particular disease.
“In the future, we want to know how this genotype—which I am sure the technology will allow us to do very quickly—affect the phenotype and the disease predisposition for each one of us,” says Dr. Diamandis.
•Mass Spectrometry
This technology has been used for many years to measure small molecules for a number of different reasons. But today, mass spectrometry can deliver scientists to the next level, allowing them to study proteins and nucleic acids. This came about with innovations in the ways of ionizing the molecules, says Dr. Diamandis. Now clinicians can take very complex mixtures of proteins, separate them and take only the spots of interest and put them into a mass spectrometer. By doing this, they can identify the protein from a tiny amount in record time.
Applying the Technology
These are just a few examples of major technologies that came about over the last few years, and scientists are now scrambling to put them into action. In his presentation, Dr. Diamandis offered some real examples of how these technologies can be applied in cancer diagnostics and classification. In explaining one example, he presented a hypothesis in which scientists acknowledged the phenotypic diversity of cancer and addressed the probability that it is accompanied by a diversity in gene expression patterns. Then they determined that the gene expression patterns can be captured by using microarrays. The idea is that if the changes can be captured, these gene expression patterns can be used for an improved taxonomy of cancer.
“The terminology that is used today is the molecular portrait or molecular signature of the cancer,” says Dr. Diamandis.
Time Will Tell
The new technology in cancer diagnosis promises to deliver better predictors of risk for recurrence and better tools to tailor the choice of treatment for individual patients. Experts contend that the tools most likely will use all of these new technologies, or at least some derivative of them.
“We will adapt some of these comprehensive technologies to be able to measure the alterations—whether they are in protein or nucleic acid—that we want to measure in the specimens that are generally available in the clinic,” says Dr. Taube. “That is the direction that development is heading.”
With the explosion of all these new technologies and the potential they offer, there is bound to be even more innovative technology development. And there will most likely be many new proposals for ways to use these new kinds of measurements. But some experts caution that such advanced technologies with so much potential will take time to fully develop and determine their true clinical value.
“What is going to take much longer is to establish any of these new proposed markers as truly valuable clinical tools,” says Dr. Lugo. “If you want to get solid answers, you have to try them out in a large group of people and that takes time because you have to wait for the clinical outcome, which varies depending on the type of tumor you are looking at.”
A lot of effort has been made to use comprehensive molecular analysis tools to find out the full range of alterations and get a profile of what the tumor cells are doing. But it may take time for scientists to figure out exactly how to use that information.
“It is going to be very difficult,” insists Dr. Taube. “There are a lot of challenges in terms of evaluating the information that we get from these tools.”
Todd Smith is an assistant editor.
References
1. Preventing and Controlling Cancer: Addressing the Nation’s Second Leading Cause of Death. A CDC Report. Accessed: www.cdc.gov.
2. Stedman’s Medical Dictionary.
3. Porstmann B. New Diagnostics Permit Customized Cancer Therapy. Accessed: www.roche.com/pages/downloads/company/pdf/rtpenzberg05e.pdf.
4. Berns A. Cancer: Gene expression in diagnosis. Nature 2000; 403:Feb. 03, 491 – 492.
