Evaluation of DNA from the Papanicolaou Test to Detect Ovarian and Endometrial Cancers

Mutant DNA from ovarian and endometrial tumors can be detected in Pap smear specimens through massively parallel sequencing. New Adventures of Old Pap Smear Patients generally do not enjoy getting a Pap smear, but the procedure has saved hundreds of thousands of lives in the decades since its inception. The now-routine smear, which allows doctors to detect abnormal cells in a woman’s cervix before they turn into an invasive cancer, was updated a decade ago to screen for DNA from human papillomavirus, the pathogen known to cause cervical cancer. Now, Kinde and coauthors have developed a technique that may make the Pap smear even more versatile by expanding it into a test for multiple cancers, including endometrial and the dreaded ovarian cancer, which is essentially untreatable unless it is caught early. The authors first assembled a catalog of common mutations in these cancers, drawing on previously published data for ovarian cancer and new data on 22 endometrial tumors. They tested 46 samples from patients with endometrial or ovarian cancers and confirmed that all 46 harbored at least some of the common genetic changes on their list. Kinde et al. then hypothesized that ovarian and endometrial cancers likely shed cells from their surfaces and that such cells may be detectable among the cervical cells in a Pap smear, if one knew how to identify them. Thus, the authors used massively parallel sequencing to test patients’ Pap specimens for some of the more common mutations found in the cancer cells. In the initial set of samples, 100% of endometrial cancers and 41% of ovarian cancers were detectable by this method. This new approach to Pap testing is not yet ready for clinical use and will not serve as a foolproof method of diagnosing genital tract tumors, particularly ovarian cancer. More research is needed to validate the current results in larger groups of patients and to improve the yield of screening for ovarian tumors, perhaps by modifying the technique doctors use to collect sample cells for the Pap test. Importantly, though, the new test has not misclassified any healthy woman as harboring a cancer, raising the possibility of its eventual use as a screening test for cancer. Even if this approach cannot identify every ovarian tumor, it may be able to detect more of them earlier and more accurately than is possible with existing methods. Once the findings of Kinde et al. are fully validated and the new test gains approval, women will have even more reasons to make sure they get their Pap smears routinely. Papanicolaou (Pap) smears have revolutionized the management of patients with cervical cancers by permitting the detection of early, surgically curable tumors and their precursors. In recent years, the traditional Pap smear has been replaced by a liquid-based method, which allows not only cytologic evaluation but also collection of DNA for detection of human papillomavirus, the causative agent of cervical cancer. We reasoned that this routinely collected DNA could be exploited to detect somatic mutations present in rare tumor cells that accumulate in the cervix once shed from endometrial or ovarian cancers. A panel of genes that are commonly mutated in endometrial and ovarian cancers was assembled with new whole-exome sequencing data from 22 endometrial cancers and previously published data on other tumor types. We used this panel to search for mutations in 24 endometrial and 22 ovarian cancers and identified mutations in all 46 samples. With a sensitive massively parallel sequencing method, we were able to identify the same mutations in the DNA from liquid Pap smear specimens in 100% of endometrial cancers (24 of 24) and in 41% of ovarian cancers (9 of 22). Prompted by these findings, we developed a sequence-based method to query mutations in 12 genes in a single liquid Pap smear specimen without previous knowledge of the tumor’s genotype. When applied to 14 samples selected from the positive cases described above, the expected tumor-specific mutations were identified. These results demonstrate that DNA from most endometrial and a fraction of ovarian cancers can be detected in a standard liquid-based Pap smear specimen obtained during routine pelvic examination. Although improvements need to be made before applying this test in a routine clinical manner, it represents a promising step toward a broadly applicable screening methodology for the early detection of gynecologic malignancies.