In a study published today in the International Journal of Cancer, Gen-Probe's APTIMA® HPV Assay provided a better combination of sensitivity and specificity than HPV DNA- or cytology-based tests for cervical cancer screening.
The French APTIMA Screening Evaluation (FASE) study was the first screening study to compare liquid-based cytology, a Pap test widely used in cervical cancer screening, with the new RNA-based APTIMA HPV test and the DNA-based Hybrid Capture 2 test (HC2). Data from 4,429 Parisian women with valid test results were analyzed.
The results showed that APTIMA HPV offered high sensitivity and specificity for the detection of high-grade precancerous lesions, the abnormal cells which could lead to cervical cancer if left untreated. The sensitivity of APTIMA HPV for detecting these precancerous lesions was similar to that of the DNA-based HC2 test and significantly higher than that of cytology. In addition, the specificity of APTIMA HPV was significantly higher than that of HC2 and similar to that of cytology.
Speaking about the results, the study's lead researcher, Joseph Monsonego, MD, Medical Director at the Institute of the Cervix, Paris, France said: "The ideal assay for cervical cancer screening should offer good specificity without losing sensitivity. High sensitivity is essential to ensure that patients with abnormal cells are detected and treated. High specificity is desirable to minimize the number of false positive results that may lead to inappropriate diagnostic procedures, over-treatment and needless anxiety in women. These data indicate that APTIMA HPV offers a combination of the high sensitivity of DNA-based tests and the high specificity of cytology. APTIMA HPV should therefore be considered as a stand-alone option for routine cervical cancer screening."
Liquid-based cytology is a type of Pap test in which a thin layer of cervical cells is collected into a liquid preservative solution. Those cells are then examined for abnormal physical changes. If the cytology test is abnormal, the patient may have a repeat Pap test, or be referred to a colposcopy procedure where the cervix is directly visualized by the physician. If one or more lesions are found on the cervix, a biopsy will be performed. The biopsy sample is examined microscopically for abnormal cellular growth known as cervical intraepithelial neoplasia (CIN) and for cancer. CIN lesions, which usually arise due to an HPV infection, are classified as CIN1 for mild cellular changes, CIN2 for moderate cellular changes and CIN3 for severe cellular changes. Both CIN2 and CIN3 lesions are indicative of abnormal cells in the cervix that could be precancerous and may need to be treated.
HPV is the cause of almost all cervical cancers, but most women infected with HPV never develop cervical disease. This is because HPV infection is often transient and cleared by the immune system. First generation DNA-based tests such as HC2 have long been used to detect the presence of HPV in the cervix. However, these tests cannot distinguish between transient infections with a benign outcome and persistent infections involved with cervical pre-cancer and cancer. The newer, second generation APTIMA HPV Assay detects messenger RNA from the viral E6/E7 oncogenes, which are involved in the development of cervical precancer and cancer. Since APTIMA HPV primarily targets the over expression of these oncogenes, it is likely to be as sensitive but more specific than DNA-based tests in detecting advanced cervical disease.
In the FASE trial, APTIMA HPV was compared with HC2 and cytology in a screening setting. Women aged 20-65 were screened by gynecologists from 17 private practices in France. Each cervical specimen collected was tested with cytology, APTIMA HPV and HC2 assays.
To help ensure the validity of the results, women who tested positive with one of the three tests were referred for additional tests. These included colposcopy and biopsy or Loop Electrosurgical Procedure (LEEP) for histological examination of the tissue, which was performed by consensus expert panel reading. Histological diagnosis is the gold standard for high grade CIN precancerous lesion assessment. In addition, to control for verification bias, a random group of 14 percent of women with normal cytology and HPV DNA- and RNA-negative tests also underwent colposcopy. If abnormal features in colposcopy were seen, these women also had a biopsy.
APTIMA HPV and HC2 were shown to be highly sensitive for the detection of CIN2+ (92.0% and 96.7%, respectively) and CIN3+ (95.7% and 95.3%, respectively). Both molecular tests were significantly more sensitive than cytology (69.1% for CIN2+ and 73.3% for CIN3+, P<0.006). The specificity of APTIMA HPV was found to be higher than HC2 for detecting CIN2+ (91.8% and 86.4%, respectively) and CIN3+ (90.3% and 84.9%, respectively), results which were statistically significant (P<0.001). APTIMA HPV and cytology had similar specificity (P<0.001). This means APTIMA HPV and cytology generate fewer false positive results than HC2. This is one of the first screening studies to demonstrate similar specificity between a HPV assay and cytology. The estimated probability of a false positive result for CIN2+ in the study was 13.6% for HC2 compared to only 8.2% for APTIMA HPV.
Commenting on the implications of the trial, Eric Lai, PhD, Gen-Probe's senior vice president of Research and Development, said: "DNA tests detect the presence of the HPV virus, whereas APTIMA HPV targets biologically relevant markers active in transforming cervical cells. DNA tests are therefore more likely to pick up transient infections and lead to false positive results with respect to disease. This study showed that in a routine screening population, APTIMA HPV had the same sensitivity as a HPV DNA test, with the low false positive rate of cytology. This means women at risk of cervical cancer could be more accurately identified. At the same time, unnecessary colposcopies, office visits, over-treatment and the associated costs could be reduced. In addition, APTIMA HPV could decrease the patient anxiety caused by inappropriate diagnostic procedures."
The tests evaluated were the APTIMA® HPV Assay manufactured by Gen-Probe, the HC2 HPV DNA test manufactured by Qiagen and the ThinPrep LBC (cytology) test manufactured by Hologic Corp.