July 2, 2007 |
A new computerised screening test for cervical cancer detects more abnormalities than the traditional smear test, according to a study published on bmj.com today.
It could also lead to fewer women needing to be re-tested and might allow for longer intervals in-between testing, says Elizabeth Davey and her colleagues.
The manual screening of conventional pap smears for cervical cancer has been around for decades but liquid-based cytology (LBC) is now replacing it in many countries.
Conventional smears are made by transferring material, taken from the cervix by a collection instrument, directly onto a glass slide. LBC slides are made by rinsing the collection instrument in liquid to produce a suspension, which is processed in a laboratory to produce a single layer of cells.
A recent study published by Guglielmo Ronco in the BMJ found that LBC did not significantly increase the ability to detect moderate (CIN2) or severe abnormalities (CIN3) compared to the conventional smear when both slides were evaluated manually by a cytologist.
In the study published today by Dr Davey, researchers used a computerised reading system, known as a Thin Prep Imager (TPI) to evaluate LBC slides. The programme would highlight any slides which needed further examination. These were looked at by a cytologist.
Samples were taken from 55,164 Australian women. From each single collection, a conventional cytology (CC) sample was made first, followed by a TPI sample.
The most important finding of the study is that the ThinPrep Imager detected 1.3 more cases of high-grade cervical abnormalities per 1,000 women screened than the conventional cytology test.
In Australia, 7.7 cases per 1,000 women screened are currently detected each year through a biennial Pap test screening programme using conventional cytology. Based on the results of this study, introducing the ThinPrep Imager would increase detection to 9.0 cases per 1,000 women screened.
Furthermore, fewer slides were found to be unsatisfactory using TPI – 1.78% compared to 3.09% with CC. Therefore, fewer women might be recalled for repeat smears than currently occurs if the ThinPrep Imager were introduced into population screening programmes.
The use of the TPI also increased detection of low-grade cell lesions and the researchers conclude this could result in higher rates of further testing. On the other hand, they say, together with the finding of improved detection of moderate and severe changes (CIN2 and CIN3), it does raise the possibility that the increased detection of abnormalities by TPI might allow longer intervals in between screening.