In the Netherlands in 2005, 65% of women attended the cervical screening programme (annual report of the regular screening programme, 2006, www.bevolkingsonderzoek.info/). By offering self sampling to non-attendees, and taking into account the 18% loss of cytology in the follow-up in this group, the real effect on attendance in the screening programme would be an extra 5.2% (6.3% (27.5% of 23%)*(100%−18%)). The total attendance in the screening programme would then increase to 70.2% (5.2%+65%). Moreover, we showed that the cumulative incidence of ≥CIN II yield in our study was 1.3% (99/7384), while the CIN lesions found via regular screening programme in 2005 was 0.8% (data received from PALGA).
Screening history of non-attendees
The finding of a twofold and more than twofold relative risk of ≥CIN II and ≥CIN III, respectively, in self sampling women aged ≥34 who did not attend the previous screening round is in line with the assumption that background risk for ≥CIN II/≥CIN III is increased after women miss one screening round. In the self sampling group, the association between screening history and CIN was independent of age (P=0.639 for ≥CIN II and 0.515 for ≥CIN III).
Strengths and limitations
We did not include a recall control group for comparison of yield of ≥CIN II/≥CIN III with the self sampling group because data from our previous work indicated that non-attendees of the regular screening programme respond poorly to any repeat invitation letter.1 Instead, we used a randomisation ratio of self sampling versus recall women in favour of maximising detection of ≥CIN II/≥CIN III in the self sampling group to allow an accurate assessment of the yield achieved by self sampling combined with HPV testing in non-attendees.
A potential bias in our attendance data could be that, unlike responders to a re-invitation for cytology, self sampling responders might have been more likely to respond for curiosity reasons, despite already being opportunistically screened before the study invitation. To address this we analysed the effect of screening history on participation via self sampling versus a second recall. When we took into account the screening history of women responders aged ≥34 in both arms, there was no indication that previously screened women would have a relatively higher preference for self sampling than women who were not screened within the past seven years.
Interestingly, self sampling responders showed high adherence to direct follow-up regimens, both at the general practitioner level (90.4%) and at the level of direct referral for colposcopy (94.5%). In size the latter is comparable with follow-up compliance of attendees of the Dutch screening programme (91%).16 Compliance after repeat testing advice (59% of women attended after one year), however, was markedly lower than observed in regular screening attendees with similar advice (86%).19 This rather low return rate might be influenced by the fact that most of these women had previous normal cytology test results after a smear taken by a physician.
In 41% of the women who had an HPV test on both self and physician collected samples, a positive result for high risk HPV in the self sample could not be confirmed in the sample taken by the physician. Most of these discrepant test results were found in women with low hybrid capture II RLU/CO values. In self sampled specimens more HPV infections of vaginal origin, including those of low risk HPV types, might be detected by hybrid capture II.20 21 22 23 24 25 Even with a cut-off level of a positive result on hybrid capture II increased to RLU/CO ≥2, there are still discrepancies between positive results for HPV in the self sampled specimens and smears taken by the general practitioner. In that case the total number of HPV positive cases would decrease from 757 to 627, but we would miss six ≥CIN II lesions (two ≥CIN II, and four ≥CIN III).
Interestingly, the yields of ≥CIN II and ≥CIN III in self sampling responders who attended the previous round and the yields in regular screening responders of the same age tested for high risk HPV by general primer 5+/6+ polymerase chain reaction (GP5+/6+ PCR) were identical (0.8% and 0.5%, respectively).26 27 This strongly suggests that the ≥CIN II/≥CIN III sensitivity of HPV testing in self sampled cervicovaginal material is not inferior to that of HPV testing on smears taken by a physician. This is in agreement with a recent meta-analysis that indicated that self sampling is as sensitive as physician obtained sampling to detect high risk HPV.25 Collectively, our data show that targeted efforts should be made to screen self sampling non-attendees who missed a previous screening round, given their increased risk of clinically relevant cervical disease.
We have also shown that the chosen triage algorithm of a cytology test on a conventional smear after an HPV positive self sample is successful. A substantial subset of the 10% self sampling women who were positive for high risk HPV, however, seemed to have negative cytology results and be negative for high risk HPV at follow-up, which in practice resulted in a marked number of unnecessary visits to the general practitioner for these women. Therefore, alternative triage tools applicable to self sampled material should be considered to prevent redundant sampling by general practitioners. In this context, molecular methylation markers,28 which are currently being investigated, are highly promising when applied to self sampled specimens. Furthermore, efforts are ongoing to improve liquid based cytological preparations of cervicovaginal lavage fluids for detecting abnormal cells.
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