These screening mammograms were reported as normal by both readers.
Ten months later the patient presented with a symptomatic lump in the left breast. She underwent diagnostic mammography.
High-grade left breast cancer with axillary lymph node involvement
Interval cancer (category 1)
The symptomatic mammograms demonstrate a new 40mm ill-defined irregular dense mass in the upper outer left breast with a large pathological left axillary lymph node. The appearances are those of primary breast cancer with axillary lymph node involvement. Given the rapid growth rate this is likely to be a high-grade cancer.
This is also an example of a screening interval cancer, which is a breast cancer diagnosed within the three-year period after a normal screening result. Interval cancers are an inevitable part of all breast cancer screening programmes, as not all cancers are detectable on mammography. Some cancers are not detectable at screening and will grow to become visible on mammography or clinically detectable in the period between routine screens. In a very small number of cases, cancers are undetected due to reader misinterpretation.
All interval cancers undergo radiological review by the screening service in order to monitor service performance and for educational benefit to image readers. It also provides helpful information for women who request the results of the review.
Interval cancers are classified into the following categories:
Category 1 (Satisfactory)
Normal or benign mammographic features
Category 2 (Satisfactory with learning points)
Seen with hindsight, difficult to perceive.
Not obviously malignant.
Category 3 (Unsatisfactory)
Appearances is obviously malignant.
Should have been recalled.
All readers reviewing the films agree that they would recall.
For every 100 interval cancers that are reviewed, approximately 80 are category 1, 13 are category 2 and 7 are category 3. Category 3 interval cancers are notifiable safety incidents and a formal apology should be issued in accordance with Duty of Candour regulations.
In this case the previous screening mammograms were reviewed, and it was agreed that these showed normal mammographic features. This was therefore classified as a category 1 interval cancer. The patient is entitled to receive the result of this review if she chooses to.
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