By Prof Patricia Fitzpatrick, Consultant Epidemiologist / Director of Evaluation, National Screening Service
We’ve published research about how interval cervical cancer rates are defined and calculated internationally. It shows that there is a clear need for international consensus on how interval cervical cancers are calculated to support benchmarking and quality improvement.
Why we did the research
Cervical cancer screening programmes help prevent cancer by detecting cell changes at the precancer stage and by detecting cancers at the earliest possible stage. Screening reduces the risk of being diagnosed with late-stage cancer. Most cervical cancers detected in women who attend screening are found before a woman develops any symptoms. Occasionally, cancers are diagnosed between screening tests - these are called interval cancers and happen in every screening programme in the world. Some cancers are detected in women who have never been screened before and in women who are overdue screening.
Understanding how cancers develop after screening can help improve screening programmes and reassure the public that the interval cancer rate in Ireland is in line with other countries.
What we did
Following an interval cancer audit in cervical screening in 2018, a national review recommended developing a clear way to define and report interval cancer rates. To support this, we looked at how other countries approach the issue and whether there is any agreement internationally. Benchmarking against other countries is a key part of quality assurance in screening as it checks whether the rate of cancers after a negative screen is within an expected range.
How we did it
We sent a web-based survey to 18 national and regional cervical screening programmes across Europe, Canada and Australia. Nine programmes responded to the survey. We asked about what types of cases they include in their definitions of an interval cervical cancer, how they calculate rates, and whether they currently report those rates.
What we found
We found that there was no consistent approach among the nine programmes that responded. Six had agreed definitions of what types of cases are considered an interval cancer, and only four were calculating an interval cancer rate. Each of these used different methods and included different types of cancer cases in their definitions.
This variation makes it hard to compare performance between programmes or to use interval cancer rates as a meaningful quality measure.
Next steps
Our study highlights a clear need for international consensus on how interval cervical cancers are defined and how interval cervical cancer rates are calculated. Consistent methods would support transparency, benchmarking, and quality improvement across screening programmes.
Since our survey, the World Health Organization’s International Agency for Research on Cancer (IARC) has published a consensus definition of interval cervical cancer. The next step involves a collaborative effort to agree on a standard approach for calculating interval cancer rates and to promote shared reporting practices. The European Joint Action on Cancer Screening (EUCanScreen) project will help to support this work.
- This research is published in the Journal Acta Obstetricia et Gynecologica Scandinavica.
Fitzpatrick P, Mooney T, Williams Y, et al. Lack of consensus in calculation of interval cancer rates for cervical cancer screening. Acta Obstet Gynecol Scand. 2025; 00: 1-7. https://doi.org/10.1111/aogs.15172
Related reading:
- Fitzpatrick P, Mooney T, Byrne H, Healy O, Russell N, O’Reilly S. Interval cancer audit and disclosure in cervical screening programmes: An international survey. Journal of Medical Screening. 2021;29(2):104-109. https://doi.org/10.1177/09691413211062344