52 - Diffusely infiltrating breast cancer of mesenchymal origin (a k a Invasive lobular carcinoma) 2/2

This is the second part of two lectures dealing with a particularly challenging breast malignancy, the diffusely infiltrating breast cancer with very special clinical and imaging features. This breast cancer subtype does not originate in the TDLUs or in the major lactiferous ducts; its origin is in the mesenchymal stem cells. The clinical and imaging presentations are dominated by the extreme proliferation of mesenchymal fibrous tissue.

This explains why there is no detectable early phase of this disease, since the supporting fibrous structure of the breast is involved from the beginning. Although it is very extensive, it is frequently missed on the mammograms because it so closely resembles the normal breast structure. As the fibrous structure thickens, the malignancy gradually becomes detectable on the mammogram, at which phase it is usually large and palpable as a thickening. Unlike other breast cancers, it shrinks the entire breast instead of causing focal skin retraction. This malignancy can be difficult to detect even in fatty replaced breasts. It is also resistant to chemotherapy and radiotherapy. The immunohistochemical biomarkers are deceptive since they are generally estrogen and progesterone positive, HER2 negative cases with 1-5% proliferation index, but the fatality rate is 30-40%.

This lecture is the continuation of Part I and includes very challenging cases for practice. Several important teaching points are emphasized throughout the lecture.