ctDNA Tests Can Provide Answers for Cancer Patients During Contrast Dye Shortage

Since JoAnn was diagnosed with stage IV lung cancer in 2016, the wife, grandmother, and educator has consistently monitored her disease to catch potential progression as early as possible.

“My mantra is always the same: Stay ahead of it,” she said.

Still, being proactive about her health became significantly more difficult during the COVID-19 pandemic, when JoAnn and other people with cancer had to weigh their need for life-saving treatments and procedures against the heightened risk of exposure during surges in virus cases. Now, they face yet another barrier to care, as the recent shortage of IV contrast media for  CT scans has the potential to delay diagnosis and restaging, leaving many to wonder about their cancer status.

Fortunately, healthcare providers have an opportunity to overcome the hurdles imposed by the CT contrast shortage by leveraging a technology that is quickly becoming a part of many cancer monitoring plans—circulating tumor DNA (ctDNA) testing. This type of test detects small traces of DNA shed into the blood by tumors, enabling the highly sensitive detection of molecular residual disease (MRD) - sometimes even before tumors become apparent on scans or by physical exam. Certain ctDNA assays, such as Natera’s Signatera test, are custom-built to detect selected mutations from each individual patient’s tumor and thus allow for highly personalized treatment and care, all from a simple blood draw.

“It empowers me to be my own best advocate with my oncologists,” said JoAnn, whose cancer status is monitored closely with Signatera. Doing so has enabled her physician to reduce the frequency of her scans, decreasing the burden of CT scans during the shortage of IV contrast media as well as sparing her from exposure to radiation. Whenever her ctDNA levels are on the rise, however, her Signatera results may serve as an early warning sign, alerting her of the need to get scans done ahead of schedule. For JoAnn, Signatera testing helps personalize her treatment journey while giving her the freedom to take control of her health.

ctDNA testing is more than simply a backup plan—it’s a value add. CT scans, for example, may not be able to pick up tumors smaller than 1 centimeter in diameter. Conversely, ctDNA tests can detect MRD down to a single molecule of tumor DNA in a single tube (about 3 tablespoons) of blood. Furthermore, studies have shown that ctDNA tests can identify cancer recurrences months or even years before traditional imaging and scans.1 Early identification of recurrence is key, as it may open up a larger window for optimizing cancer treatment decisions and improving outcomes.

ctDNA tests are typically ordered by physicians in conjunction with routine imaging studies like CT scans to monitor for disease recurrence. Their continued use during times of limited scan availability is therefore a natural extension of current practice patterns. Many ctDNA tests are already commercially available and covered by Medicare. 

For JoAnn and others living with cancer, the question of relapse is always looming in the back of their minds: Did the treatment work? Is the cancer coming back? JoAnn describes experiencing a nervous feeling she calls “scan-xiety” when anticipating test appointments and receiving scan results. These emotions are heightened by scheduling delays due to the contrast media shortage. Healthcare providers should never underestimate the value of peace of mind in such challenging times.

When new obstacles threaten to make people with cancer feel less in control, we must address them head-on, working together to embrace innovative solutions that allow us to deliver critical health information when needed most. We have the tools to help people through this; we cannot leave them waiting.

Dr. Minetta Liu is the Chief Medical Officer of Oncology at Natera, Inc. Dr. Liu was previously a professor of oncology and chair of research in the Mayo Clinic’s Department of Oncology in Rochester, MN. She is an expert in ctDNA and dedicated to developing molecular markers that allow for individualized—and potentially more effective—treatment plans for people living with cancer. 



  1. Reinert T, Henriksen TV, Christensen E, et al. Analysis of Plasma Cell-Free DNA by Ultradeep Sequencing in Patients With Stage I to III Colorectal Cancer. JAMA Oncology. 2019;5(8):1124-1131.

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