Evident test: Inside the 2-step extracellular vesicle assay

Ovarian cancer typically presented with a nonspecific constellation of symptoms that, on their own, were often insufficient to prompt a timely diagnostic workup, according to Dawn Mattoon, PhD, CEO of Mercy BioAnalytics. As a result, a significant fraction of cases were diagnosed only after emergent presentation, and 80% were at an advanced stage at diagnosis—making the disease a strong use case for screening, Mattoon said.

Mercy BioAnalytics’ investigational Evident Ovarian Cancer Screening Test runs on the company’s Mercy Halo liquid biopsy platform, which uses biomarker colocalization to analyze blood-based extracellular vesicles (EVs).¹ In September 2026, the FDA approved the company’s investigational device exemption to begin the prospective pivotal SOARA study evaluating the test in average-risk women; the test has not been approved or cleared by the FDA.²

Accessibility was a core design consideration: A blood-based test could reach rural and urban communities across all populations, beginning in the United States and expanding globally, according to Mattoon.

Many companies developing blood-based cancer detection have measured circulating tumor DNA, an approach with a technical limitation in early-stage disease.

“The challenge with measuring circulating tumor DNA is that it’s only released when a cell dies, when it goes through apoptosis or necrosis. And in the setting of early stage cancer, there’s just not a lot of that cell death that’s occurring,” Mattoon said.

Mercy instead built its portfolio around EVs, small membrane-bound particles shed continuously by every living cell, tumor and healthy alike. The central technical challenge was signal to noise: measuring only tumor-derived EVs amid the vast excess shed by healthy tissue.

The platform addressed this with a 2-step assay. In the first step, a magnetic bead coated with a capture antibody against a tumor biomarker pulled EVs out of the serum sample. Because that single marker could also appear on vesicles from healthy tissue, the capture step enriched for tumor-derived EVs but was not perfectly specific.

Specificity came from the second step. A second and third detection antibody, each directed against an additional tumor marker on the surface of the same captured vesicle, were conjugated to double-stranded oligonucleotides with complementary single-stranded overhangs. Only when the antibodies bound in close proximity did the overhangs anneal; a ligation step then formed a DNA bridge that served as a template for quantitative polymerase chain reaction (PCR).

“You only get a signal in the PCR reaction if all 3 tumor markers are present on the surface of the same vesicle, and the probability of that occurring in a vesicle that was shed by healthy tissue is just very, very low,” Mattoon said.

According to Mattoon, the abundance of EVs in circulation was intended to drive sensitivity for early-stage cancer, the colocalization requirement to drive specificity, and the PCR readout—a simple, ubiquitous method—to keep cost reasonable.

References

1. Saylor BP. FDA approves IDE for pivotal study of Evident ovarian cancer screening test. Contemporary OB/GYN. September 23, 2026. https://www.contemporaryobgyn.net/view/fda-approves-ide-for-pivotal-study-of-evident-ovarian-cancer-screening-test
2. Mercy BioAnalytics receives FDA approval to initiate prospective pivotal study of Evident ovarian cancer screening test. Press release. September 21, 2026. Accessed October 15, 2026. https://www.prnewswire.com/news-releases/mercy-bioanalytics-receives-fda-approval-to-initiate-prospective-pivotal-study-of-evidentovarian-cancer-screening-test-302885020.html