Emerging science suggests that the body’s “liquid gold” could be particularly useful for liquid biopsies, offering a convenient, pain-free, and cost-effective way to spot otherwise hard-to-detect cancers.
“The search for cancer biomarkers that can be detected in urine could provide an enormous step forward to decrease cancer patient mortality,” said Kenneth R. Shroyer, MD, PhD, a pathologist at Stony Brook University, Stony Brook, New York, who studies cancer biomarkers.
Physicians have long known that urine can reveal a lot about our health — that’s why urinalysis has been part of medicine for 6000 years. Urine tests can detect diabetes, pregnancy, drug use, and urinary or kidney conditions.
But other conditions leave clues in urine, too, and cancer may be one of the most promising. “Urine testing could detect biomarkers of early-stage cancers, not only from local but also distant sites,” Dr. Shroyer said. It could also help flag recurrence in cancer survivors who have undergone treatment.
Granted, cancer biomarkers in urine are not nearly as widely studied as those in the blood, Dr. Shroyer noted. But a new wave of urine tests suggests research is gaining pace.
“The recent availability of high-throughput screening technologies has enabled researchers to investigate cancer from a top-down, comprehensive approach,” said Pak Kin Wong, PhD, professor of mechanical engineering, biomedical engineering, and surgery at The Pennsylvania State University. “We are starting to understand the rich information that can be obtained from urine.”
Urine is mostly water (about 95%) and urea, a metabolic byproduct that imparts that signature yellow color (about 2%). The other 3% is a mix of waste products, minerals, and other compounds the kidneys removed from the blood. Even in trace amounts, these substances say a lot.
Among them are “exfoliated cancer cells, cell-free DNA, hormones, and the urine microbiota — the collection of microbes in our urinary tract system,” Dr. Wong said.
“It is highly promising to be one of the major biological fluids used for screening, diagnosis, prognosis, and monitoring treatment efficiency in the era of precision medicine,” Dr. Wong said.
How Urine Testing Could Reveal Cancer
Still, as exciting as the prospect is, there’s a lot to consider in the hunt for cancer biomarkers in urine. These biomarkers must be able to pass through the renal nephrons (filtering units), remain stable in urine, and have high-level sensitivity, Dr. Shroyer said. They should also have high specificity for cancer vs benign conditions and be expressed at early stages, before the primary tumor has spread.
“At this stage, few circulating biomarkers have been found that are both sensitive and specific for early-stage disease,” said Dr. Shroyer.
But there are a few promising examples under investigation in humans:
Prostate cancer. Researchers at the University of Michigan have developed a urine test that detects high-grade prostate cancer more accurately than existing tests, including PHI, SelectMDx, 4Kscore, EPI, MPS, and IsoPSA.
The MyProstateScore 2.0 (MPS2) test, which looks for 18 genes associated with high-grade tumors, could reduce unnecessary biopsies in men with elevated prostate-specific antigen levels, according to a paper published in JAMA Oncology.
It makes sense. The prostate gland secretes fluid that becomes part of the semen, traces of which enter urine. After a digital rectal exam, even more prostate fluid enters the urine. If a patient has prostate cancer, genetic material from the cancer cells will infiltrate the urine.
In the MPS2 test, researchers used polymerase chain reaction (PCR) testing in urine. “The technology used for COVID PCR is essentially the same as the PCR used to detect transcripts associated with high-grade prostate cancer in urine,” said study author Arul Chinnaiyan, MD, PhD, director of the Michigan Center for Translational Pathology at the University of Michigan, Ann Arbor. “In the case of the MPS2 test, we are doing PCR on 18 genes simultaneously on urine samples.”
A statistical model uses levels of that genetic material to predict the risk for high-grade disease, helping doctors decide what to do next. At 95% sensitivity, the MPS2 model could eliminate 35%-45% of unnecessary biopsies, compared with 15%-30% for the other tests, and reduce repeat biopsies by 46%-51%, compared with 9%-21% for the other tests.
Head and neck cancer. In a paper published in JCI Insight, researchers described a test that finds ultra-short fragments of DNA in urine to enable early detection of head and neck cancers caused by human papillomavirus.
“Our data show that a relatively small volume of urine (30-60 mL) gives overall detection results comparable to a tube of blood,” said study author Muneesh Tewari, MD, PhD, professor of hematology and oncology at the University of Michigan .
A larger volume of urine could potentially “make cancer detection even more sensitive than blood,” Dr. Tewari said, “allowing cancers to be detected at the earliest stages when they are more curable.”
The team used a technique called droplet digital PCR to detect DNA fragments that are “ultra-short” (less than 50 base pairs long) and usually missed by conventional PCR testing. This transrenal cell-free tumor DNA, which travels from the tumor into the bloodstream, is broken down small enough to pass through the kidneys and into the urine. But the fragments are still long enough to carry information about the tumor’s genetic signature.
This test could spot cancer before a tumor grows big enough — about a centimeter wide and carrying a billion cells — to spot on a CT scan or other imaging test. “When we are instead detecting fragments of DNA released from a tumor,” said Dr. Tewari, “our testing methods are very sensitive and can detect DNA in urine that came from just 5-10 cells in a tumor that died and released their DNA into the blood, which then made its way into the urine.”
Pancreatic cancer. Pancreatic ductal adenocarcinoma is one of the deadliest cancers, largely because it is diagnosed so late. A urine panel now in clinical trials could help doctors diagnose the cancer before it has spread so more people can have the tumor surgically removed, improving prognosis.
Using enzyme-linked immunosorbent assay test, a common lab method that detects antibodies and other proteins, the team measured expression levels for three genes (LYVE1, REG1B, and TFF1) in urine samples collected from people up to 5 years before they were diagnosed with pancreatic cancer. The researchers combined this result with patients’ urinary creatinine levels, a common component of existing urinalysis, and their age to develop a risk score.
This score performed similarly to an existing blood test, CA19-9, in predicting patients’ risk for pancreatic cancer up to 1 year before diagnosis. When combined with CA19-9, the urinary panel helped spot cancer up to 2 years before diagnosis.
According to a paper in the International Journal of Cancer, “the urine panel and affiliated PancRISK are currently being validated in a prospective clinical study (UroPanc).” If all goes well, they could be implemented in clinical practice in a few years as a “noninvasive stratification tool” to identify patients for further testing, speeding up diagnosis, and saving lives.