Could Nuclear Imaging Help Close the Endometriosis Diagnostic Gap?

A scan that could show endometriosis without surgery to find it is an easy idea to like. A small phase 2 study of technetium-99m maraciclatide gives molecular imaging a reason to keep going. It doesn’t yet give anyone a replacement for the existing diagnostic pathway.

What maraciclatide targets

According to the NIHR Biomedical Research Centre in Oxford, maraciclatide binds to an integrin associated with the formation of new blood vessels. The research asks whether that activity can help pick out endometriotic lesions, especially superficial peritoneal disease that conventional imaging can miss.

Maraciclatide is given intravenously and imaged with SPECT/CT. That’s less invasive than an operation, but calling it a simple scan skips over the injection, the radiation exposure and the specialist imaging it requires.

What the DETECT maraciclatide study measured

The published DETECT abstract describes an exploratory, single-center, open-label phase 2 study. Twenty participants were imaged and 19 completed the surgical comparison. Imaging matched the surgical finding, disease or no disease, in 16 of those 19, and detected disease in 14 of the 17 who had it.

Reported sensitivity was 82% (95% CI, 57% to 96%). Specificity was 100%, but its confidence interval runs from 16% to 100%, and for a simple reason: only two participants in the comparison turned out not to have endometriosis. A perfect score on two negative cases says very little about how often false positives will occur.

The authors say the study wasn’t powered to establish definitive diagnostic accuracy. It was funded by the NIHR Oxford Biomedical Research Centre and Serac Healthcare, the company developing the agent.

The diagnostic pathway is already more nuanced than surgery or nothing

The 2022 ESHRE guideline doesn’t require laparoscopy before care can begin for every patient with suspected endometriosis. It recommends considering laparoscopy when imaging is negative or when empirical treatment fails or isn’t appropriate.

That’s the right yardstick for a new test. Patients move through symptoms, clinical assessment, imaging, treatment decisions and, in selected cases, surgery. A claim that one scan could replace all of that would ask far more than a 19-patient comparison can support.

What a larger trial needs to answer

The next study needs enough participants without endometriosis to pin down the false-positive rate, plus a wider range of disease presentations. Independent image reading and testing at multiple centers would show whether performance holds up outside the original setting.

The clinical questions go beyond whether a lesion shows up on a scan. Does the test shorten the path to the right diagnosis? Does it change a treatment decision? Can it spare someone an unnecessary operation without delaying surgery they actually need? What does it cost, and how much radiation does it add?

Oxford’s April 2026 announcement said larger phase 3 studies are planned. Planned isn’t enrolled, and enrolled isn’t results.

Maraciclatide has earned a bigger trial. It hasn’t yet earned a place in routine care. What would matter to patients is a better route to diagnosis, shown in the people whose diagnosis is hardest to pin down.