Women who received only a primary human papillomavirus test were 58% less likely to develop grade 3 or worse cervical intraepithelial neoplasia (CIN3+) by 48 months than women who had the traditional Pap cytology screen.
The primary HPV test also reduced the 2-year risk of CIN2+ neoplasia, compared with Pap smear alone,, and her colleagues reported in JAMA.
“These results have demonstrated that primary HPV testing detects cervical neoplasia earlier and more accurately than cytology,” wrote Dr. Ogilvie of the University of British Columbia, Vancouver, and her colleagues.
(the Human Papilloma Virus For Cervical Cancers Screening trial) enrolled 19,009 Canadian women aged 25-65 years and randomized them to two cervical cancer screening paradigms: Pap liquid-based cytology (LBC) or primary HPV testing.
The intervention group (9,552) had cervical cancer screening with a high-risk HPV DNA test that detects types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68. If either test was positive, they were referred for colposcopy. If both tests were negative, they returned for their final screen with both tests at 48 months.
The control group underwent primary LBC testing, followed by HPV testing for women with atypical squamous cells of unknown significance (ASCUS). If these tests were both positive, they were referred for colposcopy. Women who were positive for ASCUS and HPV negative returned in 12 months and were referred for colposcopy if they had ASCUS or any higher-grade abnormality. At 48 months, they also returned and underwent both screening tests.
The primary outcome was the rate of CIN3+ at 48 months. Secondary endpoints included the 48-month rate of CIN2+, the threshold for colposcopy referral, and the effect of primary HPV testing on colposcopy.
In the first round of screening, HPV testing detected significantly more cases of CIN3+ than did LBC (risk ratio, 1.61). This was an absolute difference of 2.67 more cases per 1,000 screened women.
At 48 months, the rate of CIN3+ was significantly lower in the intervention group than in the control group (2.3 vs. 5.5 per 1,000; RR, 0.42). This represents an absolute difference of 3.2 fewer cases per 1,000, the investigators said.
Overall, however, the two methods detected about the same number of cases by 48 months, the investigators said.
“Cumulative CIN3+ incidence curves show no significantly different disease detection across trial groups in the intervention group. The cumulative incidence was higher earlier in the trial at 18 months and 42 months, compared with the control group. ... By the end of trial follow-up (72 months), incidence was similar across both groups.”
Women who were HPV negative at baseline reaped the biggest benefit. The 48-month HPV incidence rate among them was 1.4 per 1,000, compared with 5.4 per 1,000 in the control group. This 75% risk reduction (RR, 0.25) represents an absolute reduction of 4 cases per 1,000 women.
The intervention group was 61% more likely to have a CIN2+ result by 12 months (RR, 1.61), but 53% less likely to have it at 48 months (RR, 0.47).
“By 48 months, significantly fewer CIN2+ cases were detected overall and across all age groups in the intervention group, compared with the control group,” the team said. At 48 months, the CIN2+ rate was 5 per 1,000 vs. 10.6 per 1,000 – a 53% reduced risk (RR, 0.47) and an absolute reduction of 5.6 cases per 1,000.
Again, the benefit accrued early and mostly in women who were negative by HPV or cytology at baseline. Among these, the CIN2+ risk for the intervention, compared with the control group, was 64% lower (RR, 0.36), and the absolute difference in incidence was 6.38 per 1,000.
This early detection came at a cost, however. Colposcopies were significantly more common in the intervention group in the first screening round (57 vs. 30.8). However, by 48 months, colposcopy rates were lower in the intervention group, compared with the control group (49.2 vs. 70.5). By the end of the study, cumulative colposcopy referral rates were similar (106.2 vs. 101.5).
Dr. Ogilvie and her colleagues suggested that this ultimate similarity in colposcopy rate shows that fears about overdiagnosis with HPV testing are unfounded.
“One of the concerns for adopting HPV-based screening is the lower CIN2+ specificity of HPV testing, compared with cytology, leading to higher screen positive rates and the resulting need for more colposcopies and biopsies. Unnecessary colposcopies potentially cause unintended harm for women and increased costs to health care systems. In this trial, round 1 colposcopy rates in the HPV-tested group were significantly higher than the cytology-tested group. However, by 48 months, the colposcopy rate in the intervention group was reduced while the control group rate increased.
“This increase is partly a result of HPV and cytology co-testing at trial end. Of the 513 control-group women referred for colposcopy at exit, 304 (59%) were cytology negative and HPV positive. In the HPV-tested group, the colposcopy rate decreased in the second round of screening, which more accurately reflects the ongoing impact of HPV-based screening on a colposcopy program. The baseline colposcopy referral rate reflects what happens when HPV-based screening is first implemented, when both prevalent and incident infections will be detected,” the investigators said.
The Canadian Institute of Health Research funded the study. Dr. Ogilvie was a coinvestigator on adjunct studies funded by Hologic and Roche, designed to compare the performance of different HPV assays. Funding for the adjunct studies was not applied to the main HPV FOCAL trial.
SOURCE: Ogilvie GS et al. .