Coffee with Komen – Genetics vs Genomic Tests: What’s the Difference?

by Bryan Schneider, MD, vice president of hte Precision Genomics Program at IU Health Simon Cancer Center

Genetic and genomic testing can tell us a great deal about someone’s likelihood of getting breast cancer or which treatment options may be most effective. But there’s often confusion about these two types of tests. Both genetics and genomics are concerned with the DNA that defines us. Our genome is composed of a series of three billion letters that forms a blueprint telling every cell in our body what to do. Genomics is a newer term that describes a wider look at the overall code. Essentially, think of them as the forest or the trees.

As we consider how genetics and genomics can help breast—or any—cancer patients, there are two approaches. Classic genetics refer to what we inherit from mom and dad; our DNA blueprint is a mixture of letters from both of our parents. While the DNA from one person to another is about 99.9 percent identical, about 0.1 percent of it is different from person to person. Interestingly, it’s that 0.1 percent difference that makes each of us unique – it gives some people blue eyes and others brown; makes some people grow tall and others short. It’s that same 0.1 percent that can also increase our risk for cancer.

Often, we call this “inherited genetics” or “germ-line genetics.” Studying inherited genetics helps us determine whether or not we’re predisposed to a higher risk to cancer. This is important because it can also inform us how early we should start screening, what kind of tests we should do, whether patients may want to take medications to decrease the likelihood of getting cancer or opt for surgeries to remove the breasts or ovaries. This is an aspect of genetics that has become very powerful in terms of informing patients about their risks of cancer.

In the newer world of genetic technology, there’s an ability to step back and read the wider genomics to detect abnormalities, which we can think of as typographical errors in those DNA letters. When we examine a patient’s tumor, we can identify typos and, if the spellchecker that we’re born with doesn’t fix those typos and if they occur in the wrong place, that cell can no longer follow the instructions in its blueprint. This cell no longer respects boundaries or dies when it’s programmed to die. This is essentially cancer: a disease of typographical errors in our DNA blueprint.

This is important because we now have the ability to look across all three billion letters in our genomic code to locate those typographical errors. Sometimes, we can locate the typo that resulted in the gas pedal being stuck “on,” giving us unprecedented ability to try to match that faulty gas pedal with a specific drug known to release that pedal. Genomic testing allows us to more precisely identify what’s gone wrong in the tumor and more importantly, it can provide clues as to which drugs may be the most efficient way to kill that tumor. Genomic testing on tumors is often used with patients who have advanced cancer, in the hope that it provides some insight as to best drugs to use or best clinical trials to enter. But the use of either test continues to evolve as science advances.

With breast cancer in particular, we have offered genetic tumor testing for a long time. A good example of an inherited gene is the BRCA gene. We know that patients who inherit this alteration have an increased risk of cancer and so we may offer them early detection screenings. An example of a typographical error is HER2 amplification, which we’ve used since the 1990s as an incredibly important test to tell us about prognosis, but more importantly about the introduction of an anti-hER2 therapy, which has markedly improved survival. The current use of broader-based testing that looks across all 22,000 genes is also evolving for use with patients who have metastatic or advanced cancer. We’re completing more comprehensive testing to unlock different targets that would be similar in philosophy but different than HER-2.

Currently we’re in the early stage of genomics. Much like the first Apple computer, we’re getting a glimpse of the power and potential for this technology, but we’ve not yet perfected its use. I believe our interpretation of genomic testing results will continue to improve. Our ability to use it to better determine who will benefit will from immunotherapy will be a major game changer and eventually, I think we’ll start to use this tool in earlier and earlier disease settings, when the drug impact will be greater. In the future, we will see an evolution of improved, targeted drug combinations, and better integrated immunotherapies that will be major advances as a result of genomic testing.

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