Can Spit Help Diagnose Endometriosis? New

Endometriosis, a condition where uterine-like tissue grows outside the uterus, is a chronic disease that causes severe pain and infertility. Despite affecting nearly 190 million reproductive-aged women, diagnosing the disease remains challenging, with people having to wait an average 6.7 years for a diagnosis.¹

“We have millions of women without any diagnosis at early stage, and this is a huge issue, especially because of the impact on their life and their fertility,” said Sofiane Bendifallaha gynecologic surgeon at the American Hospital of Paris. With few reliable biomarkers, doctors traditionally diagnose the disease with laparoscopic surgery, and researchers believe that such barriers could mean that many cases go undiagnosed.^2,3

To address this issue, Bendifallah and his team collaborated with Ziwiga not-for-profit organization, to establish non-invasive diagnostic biomarkers for endometriosis.⁴ Over the past few years, they have identified salivary microRNA—small, non-coding molecules that regulate gene expression—signatures associated with the disease. Other than the clinical implications, identifying aberrantly expressed microRNAs in endometriosis could help unravel the disease biology and offer potential therapeutic targets.

“If groups are finding a panel of markers such as saliva microRNA that are indeed sensitive and specific across all patients, no matter who they are, that should tell us something revolutionary about endometriosis,” said Stacey Missmera gynecological epidemiologist at Michigan State University, who is not associated with Bendifallah’s team.

The Conventional Way to Diagnose Endometriosis

Marred by medical gaslighting, people with endometriosis often report negative experiences with healthcare professionals dismissing their symptoms.⁵ Additionally, patients can experience varied symptoms, ranging from no signs to debilitating pelvic pain and infertility, presenting challenges for initial diagnosis.

Traditionally, definitively diagnosing endometriosis requires a laparoscopic surgery, where doctors visualize the internal organs using a camera and remove potentially diseased tissue for histologic analyses.² “The difficulty with histologic confirmations is that the histologic criteria are very narrow and haven’t been updated in more than 50 years,” said Missmer.

While increasing resolution of imaging technologies such as ultrasound and magnetic resonance imaging (MRI) can help detect the disease on scans, some obstacles remain. Both Bendifallah and Missmer noted that these methods are subjective based on the healthcare provider. “(It depends) on what their beliefs still are about what endometriosis looks like or doesn’t (look like),” said Missmer.

Bendifallah added, “We have imaging, we have surgery, and we still have more than 10 years of delay (to diagnosis), which mean this is not accurate enough.” This prompted him to search for alternative methods to reliably diagnose the disease.

Why Salivary microRNAs?

Since their classification in the early 2000s, researchers found aberrant microRNA expression in diseases like cancer and gynecological conditions.⁶ Over time, scientists discovered different microRNA expression profiles in the uterine lining and of women with and without endometriosis.⁷

Most microRNAs are located within cells, but some microRNAs such as circulating or extracellular microRNAs are released into bodily fluids such as blood and saliva. While some researchers found different expression of microRNAs in the blood of endometriosis patients, it was not a reliable biomarker.⁸ Bendifallah and his team investigated an alternative. “We do believe, when we started this project, that it will be possible to find these microRNAs in the saliva,” he said.

So, the researchers sequenced the microRNAs in saliva samples collected from 200 people who showed signs of endometriosis.⁴ Laparoscopic surgery or MRI helped detect endometriosis, and the researchers identified microRNAs that were differentially expressed in people with and without the disease. They trained a machine learning algorithm to predict the disease state based on the microRNA signature, and applying this model to their dataset yielded a panel of 109 microRNAs predictive of endometriosis with almost 96 percent sensitivity and 100 percent specificity.

A Non-Invasive Test Can Reduce Diagnostic Barriers

While Missmer is cautiously optimistic about the initial results, she noted that the test may not be completely unbiased and may overestimate values because of selecting only the patients that most definitively have endometriosis. “I think that there are diagnostics that will work well for most patients, (but) I’m dubious that there is a non-invasive diagnostic that will work for all patients,” she said. “We have not found anything yet that is consistent across all patients,” she explained, including symptoms and treatment responses. She added that the key would be to investigate the biomarkers in a broader population.

To validate the diagnostic accuracy of their pilot test, Bendifallah and his team recruited another 200 participants.⁹ Applying their model to this cohort across multiple centers revealed a sensitivity of 96 percent and specificity of 95 percent, validating the test’s diagnostic power.

The saliva test is now used in clinical practice in France. But Bendifallah noted that it is not meant to replace diagnostic imaging; rather, it is intended to complement it. “When the imaging is not able to see the lesion, especially because the lesion is (at a) difficult location, the saliva test is of value at this moment,” he explained. Such a definitive diagnosis could help physicians decide the best course of treatment and avoid surgery unless absolutely required.

Despite her skepticism, Missmer said, “I would love for these groups to be successful.” Although the tests are expensive, a non-invasive method may reduce diagnostic delay, she said. “It’s what we do with that earlier diagnosis (that matters),” she added. “Then it is on us and the clinical and scientific world to make sure that something good happens for them next.”