USC Norris opens a Phase 1 trial of a blood test to pair with mammograms for Stage I breast cancer

More than 300,000 women in the U.S. receive a breast cancer diagnosis each year, Discover reports ^[9]. The write-up does not give an enrollment figure, an accuracy target or a description of who is being enrolled.

It does give a design. Participants provide two blood samples a year apart, and researchers compare the findings with patients' diagnoses to assess accuracy ^[6]. In our view, diagnosis is a sensible reference standard for a first look. We'd expect the second sample to let investigators ask whether a signal appears before a diagnosis does.

Liquid biopsies already have a role in cancer care, often to track treatment or check whether a diagnosed cancer has returned ^[3]. Many look for DNA fragments shed by cancer cells, and a small tumor may not shed enough to find ^[2]. This test looks for more than DNA. It searches for rare cancer-associated cells and tumor-associated large extracellular vesicles (L-EVs), which are tiny despite the name ^[1]. Screening for a cancer nobody has found yet is a different job from monitoring one that is known, and this trial is the first test of whether those cells and vesicles can do it.

Martynova framed the aim as a question. "Our hope is to determine whether this test can provide more information about breast cancer screening and detection, particularly during the stages of the disease when it may be easier to treat," said principal investigator Anastasia Martynova in a press release ^[10]. She was more specific about the particles: "These particles could potentially give doctors an additional sign of cancer, especially at early stages when other tests might not be able to detect it," Martynova said ^[12].

A comparison with diagnoses shows how often the test agrees with the clinic, but says nothing about whether finding a cancer earlier changes treatment or survival. Accuracy also has two halves: catching cancers, and correctly clearing women who do not have one. The reported design speaks to both only if the analysis breaks them out.

Co-investigator Amanda M. Woodworth described where the test could fit if it works. "If the test is shown to be effective, it could offer an additional screening option for women who face barriers to mammography, such as those who live in remote areas where access to screening services is limited," Woodworth said ^[11]. She also named women who have had a mastectomy, for whom mammograms are no longer an option ^[11].