Quantification of the UK 5-point breast imaging classification and mapping to BI-RADS to facilitate comparison with international literature

Objective: The UK 5-point breast imaging scoring system, recently formalised by the Royal College of Radiologists Breast Group, does not specify the likelihood of malignancy in each category. The breast imaging and reporting data system (BI-RADS) is widely used throughout North America and much of Europe. The main purpose of this study is to quantify the cancer likelihood of each of the UK 5-point categories and map them to comparable BI-RADS categories to facilitate comparison with North American and European literature and publication of UK research abroad. Methods: During the 8 year study period, mammogram and ultrasound results were UK scored and the percentage of cancer outcomes within each group calculated. These were then compared with the percentage incidence of the BI-RADS categories. Results: Of 23 741 separate assessment episodes, 15 288 mammograms and 10 642 ultrasound examinations were evaluated. There was a direct correlation between UK scoring and BI-RADS for categories 1 and 5. UK Score 2 lipomas and simple cysts correlated with BI-RADS 2, with the remaining UK Score 2 lesions (mostly fibroadenomas) assigned to BI-RADS 3. BI-RADS 4 incorporates a wide range of cancer risk (2-95%) with subdivisions a, b and c indicating increasing, but unspecified, likelihood of malignancy. UK Score 3 correlated with BI-RADS 4 a/b and UK Score 4 corresponded with BI-RADS 4c. Conclusion: This study quantifies the cancer likelihood of the UK scoring and maps them to parallel BI-RADS categories, with equivalent cancer risks. This facilitates the ability to share UK research data and clinical practice on an international scale.