Genetic testing of tumors is becoming increasingly common in cancer care. The molecular alterations found in a tumor can provide critical information for making an accurate diagnosis and determining the best treatment.
Although current clinical testing usually focuses on a panel of specific mutations, cancer centers are developing programs to analyze entire cancer genomes routinely — an approach made possible by cheaper sequencing costs — in order to individualize care. This process raises a thorny issue: What happens when a genome analysis of a person’s tumor reveals that he or she is at risk for developing a different type of cancer or other disease?
Recently, Memorial Sloan-Kettering Clinical Genetics Service Chief Kenneth Offit, Clinical Genetics Service Clinic Director Mark E. Robson, and researcher Yvonne Bombard published a viewpoint in the Journal of the American Medical Association regarding this question of incidental genetic findings, which cancer researchers have dubbed the “incidentalome.”
We asked Dr. Robson to discuss some of the issues surrounding accidental genetic findings and what Memorial Sloan-Kettering is doing to address them.
What is an example of a genetic variation that might be discovered by accident while sequencing the genome of a patient’s tumor?
For instance, you could be sequencing a lung cancer tumor in search of an EGFR mutation to target with an anticancer drug, and find a mutation in BRCA1, which is associated with increased risk for breast and ovarian cancer. Since most of a tumor’s DNA sequence is identical to the sequence of a normal cell from that same patient, this additional variation is probably inherited — and is what is called a germline mutation.
In that situation, are you obligated to inform the patient? It’s a very complex question. There are many variables to consider, such as individual preference, whether anything can be done to control risk, and whether other people — such as close relatives — may be affected.
Has this actually become a problem for doctors and researchers, or is it still a hypothetical situation for now?
Right now, most clinical testing of tumors is for a relatively limited number of specific mutations, not the full genome. But soon we’re going to be testing for a much broader panel of genes, increasing the chances of incidental findings.
On the research side, it’s quickly becoming an issue. Many tumor samples that have been stored in tissue banks for years or decades are now being fully sequenced. If incidental discoveries are made during that process, is there an obligation to try to find those patients and inform them? This has not been established, and there are obvious practical barriers. We need to lay the intellectual groundwork now for how we’re going to respond to these questions.
What steps have been taken at Memorial Sloan-Kettering to address the issue?
This summer, our Institutional Review Board (IRB), which oversees all of our patient-related research, updated part of our patient consent policy. When patients agree to have a tissue sample taken, they are asked whether they are open to being re-contacted if an investigator finds something that might affect their health.
Under the new procedure, if a researcher finds something that might be important to communicate to the patient, the specific question will be put before the IRB and carefully considered. If there is agreement the information should be conveyed, and the patient has indicated that he or she wants to be re-contacted, we’ll reach out to that person. We think this protects the people participating in our studies without restricting important research.
With all the genetic research taking place at Memorial Sloan-Kettering, is the IRB facing a deluge of these cases?
So far, no. The way the analyses are being conducted is that the computer looks for mutations in specific spots and subtracts all other information about the inherited genetic sequence before the investigator sees it. In other words, if you have genetic variants present in the tumor that are also in the normal cells, they are being filtered out by the software. The investigator ends up seeing variants that are only in the tumor.
As we pointed out in the JAMA paper, this is one way of limiting potential incidentalome issues.
But some researchers don’t have the germline DNA sequence available for comparison purposes, so while sequencing the tumor they see potentially relevant variations. For example, they could be sequencing a prostate cancer genome and see a mutation in the BRCA1 gene, which increases risk of other cancers.
The question becomes, under what circumstances do you tell the patient, and what about the patient’s siblings or children who may carry the mutation as well? In addition, sometimes multiple variants associated with disease risk may be found — and how do we provide counseling for all of them at once?
Have you gotten a sense from patients about what their preference usually is regarding being informed of these incidental genetic discoveries?
Commonly, people say, “I want to know everything,” but the devil’s in the details when you start considering the risk for diseases that can’t be prevented or treated. We are setting up focus groups of patients and unaffected people to try to understand how people think when they are confronted with these situations and how they prioritize different types of genetic information. We also have an active IRB protocol in which we are giving people who had their sequence determined as part of research studies the opportunity to learn their results.
Right now, it’s not clear what the dividing lines are. We want to reach a point where mutations are sorted into different categories, where certain incidental findings are nearly always appropriate to communicate to patients, others almost never so, and some require more context to determine.
We’re moving from the traditional model of asking patients if they would like to hear the results of a specific test before that test is performed, to this brave new world where we’re trying to help people make decisions about genetic information revealed by accident that is not possible to fully anticipate. It’s a very complicated issue, but it also offers a tremendous opportunity to benefit patients.
If you are interested in participating in the focus group, call 646-888-4867. Everyone is welcome, including patients, relatives, Memorial Sloan-Kettering employees, and the general public. No sequencing is provided.