New Blood Test Can Detect Cancer: 5 Things to Know

Cancer screenings help diagnose the disease earlier, when it’s easier to treat. Unfortunately, only 14 percent of cancers are detected with a routine screening test.

A new blood test, called Galleri, tests for more than 50 types of cancer with a simple blood draw. Jordan Winter, MD, Chief of Surgical Oncology at UH Seidman Cancer Center, shares more.

How Does the Galleri Test Work?

The Galleri test looks for markers in the blood that can indicate cancer, including hard-to-detect types such as pancreatic and esophageal cancers.

“All cells, including cancer cells, release DNA fragments into the bloodstream when they die,” says Dr. Winter. “These fragments are called cell-free DNA. With a single blood draw, the Galleri test looks for cell-free DNA and identifies whether it comes from cancer cells or healthy cells.”

The Galleri test can also provide information about where the cancer cells originated in the body. This information helps guide next steps to confirm or rule out a cancer diagnosis.

Who Should Get the Galleri Test?

The Galleri test isn’t part of routine cancer screening recommendations, and it isn’t covered by insurance. Dr. Winter identifies two groups of people who should discuss it with their doctor:

1. People of any age with symptoms that could indicate cancer, such as unintentional weight loss, change in bowel habits, blood in the urine, etc.
2. People over age 50 without symptoms, because cancer risk increases with age.

What Does a Positive Result Mean?

The Galleri test is used to screen for cancer, not diagnose it. If you receive a positive result, additional diagnostic testing is required to confirm if cancer is present. The test can also fail to detect cancer in some cases.

“It’s important for doctors who prescribe the test to inform their patients that the test is only a stepping stone to other diagnostic testing if a positive result if found,” Dr.  Winter says. “I recently explained to an older relative that her negative Galleri test result did not necessarily mean she doesn’t have cancer, and that it’s important for her to continue to get her age-recommended cancer screenings.”

How Accurate Is the Galleri Test?

In a recent study, 4 out of 10 people who received a positive test result were diagnosed with cancer.

“A predictive rate of 40 percent is actually very good in the cancer screening world,” Dr. Winter says. “To put that number into perspective, the rate for other cancer screenings are much lower than the Galleri test. For example, the predictive rates for routine mammography for breast cancer screening and CT chest scans for lung cancer screening are only about 5 to 10 percent.”

Overall, the test’s sensitivity is about 50 percent. This means that for people who have cancer, the Galleri test will detect it about half of the time. The Galleri test has a low false-positive rate of about 0.5 percent, meaning only 1 in 200 people without cancer will receive a positive result.

Is the Galleri Test Worth It?

“Galleri is the first test of its kind,” Dr. Winter says. “It’s not perfect, but that doesn’t mean we shouldn’t use it. The opportunity to detect half of all cancers before they would’ve been and to improve patient survival rates is a game-changing advance in cancer care.”

Dr. Winter says he expects false-positive and false-negative rates to improve in later versions of the Galleri test and in other multi-cancer early detection tests currently in development.

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