Studies have shown that primary screening with HPV testing, when combined with various forms of triage, offers greater security than cytology, and at longer screening intervals (Tota & Ratnam ). Furthermore, it has been argued that, with the introduction of child HPV vaccination, there will have to be shift from cytology to HPV testing in primary cervical screening in any case (What is the future of cervical screening?/STI/blogs). Yet some uncertainty remains as to how cervical screening will look in the post-vaccination era. Canfell & Saville cast some light on this uncertain future with what they claim to be the first trial of HPV-based primary screening in a partly vaccinated population (i.e. one to whom vaccination has been offered). The Australian national HPV vaccination programme began in 2007 for females. The ‘Compass’ randomized trial, which includes over a quarter of participants (c. 1,100/5000) from the vaccination era , compares primary screening using 2.5 yearly liquid-based cytology (LBC) with 5-yearly HPV screening followed by one of two alternative triage regimes (LBC or dual stained cytology).
This study, like earlier ones, found a significantly higher detection rate of cervical intraepithelial neoplasia (CIN) grade 2 (and 3) with primary HPV screening. Initial levels of referral for colposcopy were raised, as expected – but not to the extent that might have been predicted. Overall, the levels of detection of CIN2+ for LBC, HPV testing with LBC triage, and HPV testing with dual stained cytology triage were 0.1%, 1.0% and 1.2% respectively, and the corresponding levels of colposcopy referral were 2.7%, 3.8% and 3.9%. Rates for the vaccinated sub-group were in proportion with this: notably, detection of CIN2+ for the same three groups at 0.5%, 2.6% and 2.9%, and colposcopy referral at 4.7%, 8.1% and 8.9%.
The Compass trial is acting as a sentinel experience for programme transition, and Australia is planning to transition to primary HPV screening on 1 December 2017. Along with the obvious advantages of higher levels of detection of abnormalities and longer intervals between tests demonstrated by Compass, there is another advantage of primary HPV screening brought to attention in a number of recent studies that could be particularly relevant to limited resource settings. This is the possibility of self-sampling, of reduction in the number of clinical specialists required and of greater access to screening. HPV screening through self-sampling has been shown to be both feasible and acceptable to patients, and to be nearly as sensitive as clinician-based sampling (Mitchell & Ogilvie/STI; Nelson & Arnold/STI; Guan & Qiao/STI).