Researchers at Johns Hopkins Medicine have developed a new, highly accurate urine test that can predict whether a woman is likely to develop cervical cancer. The test examines epigenetic changes in both human genes and in HPV genes, showing better accuracy in identifying premalignant cervical lesions than currently used genetic tests.
The study, “Molecular Triage of Premalignant Lesions in Liquid-Based Cervical Cytology and Circulating Cell-Free DNA from Urine, Using a Panel of Methylated Human Papilloma Virus and Host Genes,” published in Cancer Prevention Research, may reduce the number of unnecessary cervical biopsies and may improve cervical cancer screening in countries where a Pap test is not a viable option.
In a previous study, the researchers had identified three genes associated with cervical cancer or premalignant lesions in the cervix. These genes, FKBP6, INTS1, and ZNF516, were found to accumulate methyl groups in their DNA as the disease progressed. This type of epigenetic modification, called methylation, suppresses the expression of these genes.
To understand whether the extent of methylation of each of the described genes could be used to discriminate healthy women from women with precancerous lesions or cervical cancer, the researchers tested 214 cervical cell samples collected during Pap smears in women ages 18 to 86. Among the samples, 34 had no abnormalities, 87 showed one of three types of precancerous tissue, and 90 showed clear evidence of cervical cancer.
Using advanced genetic techniques, the researchers then analyzed the DNA of the cervical tissue samples, comparing the number of methyl groups in each of the described genes in samples from the 34 healthy women to 53 precancerous samples.
Results showed that the extent of methylation had a 90 percent sensitivity and 88.9 percent specificity in discriminating precancerous lesions from healthy samples. This meant that gene methylation identified 90 out of 100 precancerous lesions, and that out of 100 healthy samples, the method could identify 88.9.
But according to the study’s first author, Rafael Guerrero-Preston, “when developing a new cancer screening test, we want something in the range of 90 to 95 percent sensitivity, which is competitive with the effectiveness of tests developed and now marketed in Europe,” which led the researchers to test yet another approach.
Since the HPV gene HPV16-L1 is also known to become methylated in human cells as cervical cancer progresses, the researchers added this gene to the panel. This time, as they tested the four-gene combination in 115 women ages 21-49 from Puerto Rico, they obtained a 90.9 percent sensitivity and a 60.9 percent specificity.
Next, they sought to assess whether this test worked with freely circulating DNA from the blood and urine instead of DNA taken directly from the cervical tissue. Their results showed that it did.
Indeed, circulating cell-free DNA isolated from the blood had an 85.7 percent sensitivity and a 60.9 percent specificity, whereas circulating cell-free DNA from the urine had a 75 percent sensitivity and an 83.3 percent specificity.
“If further studies confirm these findings, we see a significant use of urine screening as a way to quickly and inexpensively determine if a biopsy is warranted, or if physicians can use a ‘watch and wait’ approach before intervening,” Guerrero-Preston, DrPH, MPH, assistant professor of otolaryngology-head and neck surgery at Johns Hopkins University School of Medicine and member of the Johns Hopkins Kimmel Cancer Center, said in a press release.
Usually, women who test positive for HPV and have an abnormal Pap smear are recommended to undergo a biopsy to exclude cervical cancer. But previous studies have shown that more than half of these biopsies are unnecessary and associated with high levels of stress. The new urine test, which provides a result in just four days, may help reduce the number of unnecessary biopsies.
“Our urine test would serve as a molecular triage,” Guerrero-Preston said, “at times supplementing Pap test information. In developing countries that don’t have the money, medical infrastructure or cultural approval for Pap test, our test could be used instead.”