WHOLE GENOME SEQUENCING FOR CANCER CARE
BY Andrea Mongler
Illustration by Abigail Goh
Three billion is such a large number that it’s hard to fathom.
To put it in perspective:
- 3 billion seconds is about 95 years
- If you took 3 billion steps, you could walk around Earth at its equator more than 45 times
- Stacking 3 billion pennies would result in a tower nearly 3,000 miles tall
Three billion also happens to be the number of DNA building blocks, or base pairs, that make up a human genome. And nearly every single cell in our bodies contains two copies of those 3 billion base pairs.
Together, the base pairs that make up our DNA provide the instructions our bodies need to develop, survive and reproduce. They’re like a massive instruction manual packed into a very tiny space. And reading that instruction manual may be the best way to figure out which cancer patients need aggressive treatments to survive.
Oncologists have long known that no two cancer patients are alike. While some patients have fast-moving cancers that will lead to death if they’re not treated quickly and aggressively, others have less severe disease that doesn’t require aggressive treatment.
This is why oncologists tailor treatments to individual patients. There’s no one-size-fits-all approach. And since cancer results from genetic mutations, oncologists’ ability to decide on the best treatment for individual patients often hinges on their ability to accurately identify mutations in a patient’s cancer through genetic testing.
The original form of genetic testing, called karyotyping, involves looking at a patient’s chromosomes under a microscope. It’s still in routine use today, and it’s usually combined with other lab tests, which means oncologists need to interpret and integrate a variety of test results. They use these test results to place patients in risk categories and guide treatment decisions.
“Genetic analysis of cancers often requires multiple testing approaches—some that use technology that’s nearly 50 years old,” says David Spencer, MD, PhD, oncologist at the Alvin J. Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine. Spencer also is the medical director of the clinical sequencing facility at Washington University School of Medicine’s Elizabeth H. and James S. McDonnell III Genome Institute. “But if we could quickly obtain a comprehensive genomic profile of a patient up front with one test, it would be a much more effective and efficient way to decide on appropriate treatments.”
Recently, Spencer and colleagues demonstrated that this is possible using a process called whole genome sequencing. Specifically, their research showed that whole genome sequencing is often a more accurate way than conventional testing to stratify patients with acute myeloid leukemia (AML) into risk categories and make treatment decisions accordingly. They also showed that this approach was fast and cost-efficient. Their research holds promise not just for AML patients but also for cancer patients more broadly.
To understand what whole genome sequencing is and why it’s such a promising strategy, it helps to first understand the genome.