Infiltrating ductal carcinoma left breast
On the initial image, the lesion is way too radiodense to be a lymph node, even with the benefit of the ubiquitous retrospectoscope. Lymph nodes on mammogram are invariably low density and have a fatty hilum or center. A lesion this dense is a red flag even without previous imaging.
On the next image after one year, the lesion is slightly larger than a year ago. Second red flag.
On the last study, the lesion is clearly pathological. By now, the initially normal nodes in the vicinity are also denser than on the initial study.
The ultrasound study shows a solid lesion as tall as it is broad. Third red flag just went up.
This is in effect "time-lapse" mammography that shows the development of an infiltrating ductal carcinoma over 3 years. The teaching point: not all lesions in the upper outer quadrant of the breast are lymph nodes. Nodes are low density and well defined, invariably with a fatty hilum or center. Dense lesions should raise a red flag. Enlarging dense lesions are doubly sinister.
Take a moment and compare this case with case 21438. The difference should be obvious.