We’ve recently measured our rate of interval cancers in BreastCheck.
What is an interval breast cancer?
This is a breast cancer that is diagnosed within 24 months (2 years) of a woman’s last breast screening, that was reported as normal, where no evidence of cancer was found.
Why is it important to measure the interval breast cancer rate?
Interval cancers happen in every breast screening programme in the world. Measuring the interval cancer rate assures us of the quality of our BreastCheck programme. It’s one part of a system of internationally accepted measurements of how well we are performing against our quality standards.
This helps us to better inform women about the benefits and limitations of breast screening, so they can make an informed choice about taking part in screening.
How we measure the interval breast cancer rate
We use two methods to measure interval breast cancer rates:
- by screening outcomes: we measure the number of interval cancers as a rate per 10,000 women screened who had a normal screening result.
- by comparison to expected rates: we compare our interval breast cancer rate as a percentage of the expected rate if there was no screening programme.
Both are done at two time points:
- 12 months after screening
- 24 months after screening.
BreastCheck standards and our interval cancer rates
Our standards for quality assurance in mammography screening are based on international guidelines. These standards include targets for interval cancer rates:
- 12 months after screening: the target is fewer than 7.5 breast cancers for every 10,000 women screened – our BreastCheck rate was between 4 and 5.
- 24 months after screening: the target is fewer than 12.5 breast cancers for every 10,000 women screened – our BreastCheck rate was between 11 and 12.
- 12 months after screening (as % of expected rate): the target is below 30% of the expected rate – our BreastCheck rate was between 17% and 20%.
- 24 months after screening (as % of the expected rate): the target is below 50% of the expected rate – our BreastCheck rate was between 44% and 47%.
Using both methods to measure, our interval cancer rate in BreastCheck is within our programme’s standards for quality assurance. This is a good result. This tells us that our programme is performing well.
How we calculated our rate
We worked with the National Cancer Registry of Ireland (NCRI) to develop a clear and detailed protocol for the safe and accurate exchange of data in compliance with the legislation.
The NCRI records new cases of breast cancer, including information on diagnosis, stage, and treatment. We sent details of BreastCheck participants who had a screening mammogram during the period 2017 to 2018 to the NCRI. They matched the BreastCheck participants who did not have a cancer detected at screening against the people on their database who had developed breast cancer in the 24 months following a BreastCheck screening mammogram. We did the calculations and the NCRI acted as our expert checker to confirm them.
Next steps
We’ll continue to work with the NCRI to examine the interval breast cancer rates, as part of our quality assurance standards.