Sclerosing adenosis is a low power diagnosis. It arises in a terminal duct lobular unit, hence the term 'lobulocentric'. Glands and tubules are compressed by a fibrotic or sclerotic stroma, and one can almost draw a circle around this lesion.
A higher power image demonstrates compressed glands and tubules composed of epithelial and myoepithelial cells. In certain lesions, the myoepithelial cells will predominate as demonstrated by spindle-shaped cells with fibrillary cytoplasm, as seen in this image. In other instances, it may be difficult to visualize a clear myoepithelial layer, therefore, a p63 and smooth muscle myosin stain will highlight the myoepithelial cells. This is helpful in distinguishing invasive carcinoma from sclerosing adenosis.
Retention of the lobular architecture can be discerned in some areas. Scattered microcalcifications, seen as dark purple irregular nodules, often with cracking, frequently accompanies sclerosing adenosis.
The extent of intervening sclerosis can vary, and when it becomes more pronounced, the lumens become compressed. The lobular nature of the lesion is still appreciable however.
Proliferation of small angulated glands and the corresponding calponin/p63 immunostain shows strong staining of the basal cells confirming the benign nature of the lesion.
Sclerosing adenosis is placed under the risk category of 'proliferative lesions without atypia' and confers minimal risk of invasive breast cancer. However, sclerosing adenosis is important to recognize because it has features that can mimic invasive carcinoma mammographically (architectural distortion and microcalcifications). Histologically, it can also simulate invasive tubular carcinoma due to its compressed and angulated glands.
Can occur in all ages. May sometimes present as a palpable mass on exam, especially if it is 'nodular adenosis' variant.
Benign. Note, however, that sclerosing adenosis may be involved by LCIS or DCIS.
1 O'Malley FP, Pinder SE. Breast Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elvesier; 2006:85-90.