Adding Pap to plasma testing boosted detection of ovarian tumors
NATIONAL HARBOR, MD. – Combining a liquid-based Pap smear and cell-free DNA plasma testing can boost the sensitivity of screening for primary ovarian tumors, based on the results of a prospective study of 201 patients.
The approach, however, was most sensitive when women already had late-stage disease, Amanda Nickles Fader, MD, said at the annual meeting of the Society of Gynecologic Oncology. Nonetheless, she called combined Pap and plasma testing “a promising step toward a broadly applicable screening methodology for the early detection of ovarian cancer.”
Ovarian cancer is a “legal malignancy,” and detecting it at “earlier, more curable stages is a clinical imperative,” said Dr. Fader of the Johns Hopkins Kelly Gynecologic Oncology Service in Baltimore, Md.
Routine screening with ultrasound or the CA-125 test has not been shown to reduce deaths from ovarian cancer and can lead to unnecessary diagnostic surgeries. Therefore, population-based screening is not recommended by the U.S. Preventive Services Task Force, the American Cancer Society, the American Congress of Obstetricians and Gynecologists, or the National Comprehensive Cancer Network, Dr. Fader noted.
This paradigm, however, is starting to change with the advent of DNA-based tests for ovarian cancer, including the PapGene test and assays for circulating DNA released by apoptotic tumor cells (ctDNA), Dr. Fader said. In a previous pilot study, Pap testing identified oncogenic driver mutations in 41% of primary ovarian tumors. In another study, polymerase chain reaction (PCR) testing detected ctDNA in more than 75% of metastatic solid tumors.
Might combining Pap and plasma testing for ctDNA further boost sensitivity? To test this idea, Dr. Fader and her associates performed liquid-based Pap tests and collected plasma from patients just before they underwent surgery for primary ovarian cancer.
They purified DNA from the Pap tests and used a Safe SeqS assay to amplify for 18 genes with known driver mutations in ovarian cancer: AKT1, APC, BRAF, CDKN2A, CTNNB1, EGFR, FBXW7, FGFR2, KRAS, MAPK1, NRAS, PIK3CA, PIK3R1, POLE, PPP2R1A, PTEN, RN F43, and TP53. Plasma DNA was purified and amplified for 16 genes of interest: AKT1, APC, BRAF, CDKN2A, CTNNB1, EGFR, FBXW7, FGFR2, GNAS, HRAS, KRAS, NRAS, PIK3CA, PPP2R1A, PTEN, and TP53. Tests were considered positive if they identified at least one driver mutation.
By itself, the Pap test identified only 34% of cases of stage I or stage II ovarian cancer and only 37% of cases of stage III/IV cancers, for an overall sensitivity of 36%, Dr. Fader reported. Likewise, ctDNA plasma testing yielded sensitivity values of 34% in stage I/II disease and 54% in stage III/IV disease. But combining these assays yielded sensitivities of 64% for stage I/II ovarian cancer and 97% for stage III/IV cancer, for an overall sensitivity of 76%.
Driver mutations most often involved the TP53 gene, followed by PIK3CA and CDKN2A. Rarer mutations included those of PTEN, KRAS, NRAS, APC, POLE, and PPP2RIA, Dr. Fader said. Study participants were 20-79 years old, with a median age of 61, and about 70% had stage III or stage IV disease. Nearly three-quarters of tumors were serous adenocarcinomas, of which 65% were high grade. Other tumors were mucinous (10%), clear cell (5%), germ cell (3%), carcinosarcomas (2%), or sex cord stromal (1%).
There was less detection of early-stage disease in this study, even though the investigators used a sensitive test that identified relatively rare driver mutations, Dr. Fader said. So far, ctDNA testing seems to be more effective for detecting metastatic ovarian cancer, she said. Future studies should further refine DNA detection by adding Tao Brush testing and should evaluate Pap and plasma testing in a larger cohort of women with early-stage ovarian cancer or precursor lesions, including carriers of BRCA mutations, she added.
Dr. Fader did not acknowledge external funding sources. She reported having no conflicts of interest.