Rarely seen, extensive, but a frequently missed and often fatal cancer
This is the first part of two lectures dealing with a particularly challenging breast malignancy, a diffusely infiltrating breast cancer with very special clinical and imaging features. It originates in the mesenchymal stem cells (not in the lobules and not in the lactiferous ducts). 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%.