Geographical distribution of breast cancers on the mammogram: an interval cancer database.

Auditing interval cancers is an important part of a breast screening radiologist's continuing education. We set out to determine whether the position of interval cancers on the mammogram differs from those detected at screening. The 773 interval cancers so far identified, and the first 200 screen detected cancers, have been entered onto a Microsoft Access 97 database developed to record pathological and radiological features, including the position of the cancer on a stylized diagram using a "point and click" system. Reports were generated showing positions of all interval cancers by classification and reader. The distribution of true interval cancers is statistically different from screen detected cancers on both views. The distribution of the false negative and screen detected cancers only differs on the oblique view. False negative and true interval cancers are of the same distribution on both craniocaudal and oblique views. However, these differences do not appear to be practically useful when applied to individual readers. We have developed a database that allows systematic recording of pathological and radiological information regarding breast cancers. Additionally, it can record the geographic position of the cancer with minimal memory requirements. Statistical differences in the distribution of false negative and screen detected cancers have been demonstrated and the stylized diagrams reinforce the importance of the conventional review areas. Although this has not identified any "blind spots" in our own readers, it nevertheless provides film readers with a tool to audit their own work.