Microarchitectural changes


Adenosis is associated with an increase in acini and glandular tissue. There may be an increase in the myoepithelial component and in the connective tissue of the lobule.

Figure 17.18. Histological appearances of fibrocystic disease - cyst formation, fibrosis and sclerosing adenosis (x150).

Sclerosing adenosis

This is characterised by prominent intralobular fibrosis and proliferation of small ductules or acini. The fibrosis may be extensive resulting in dense spiculated strands with prominent architectural distortion of the normal breast pattern. Complex sclerosing lesions are variants of this but are associated with prominent epithelial hyperplasia. In addition, there may be an increase in the myoepithelial component. As a result of the accumulation of dense fibrous tissue these lesions may be difficult to differentiate clinically and mam-mographically from breast cancers.


This is characterised by hyperplasia of the epithelium lining the terminal ducts and acini. The proliferation of epithelium may result in a solid mass with obliteration of the ducts or it may take the form of epithelial projections which grow into the ducts (ductal papillomatosis). The morphological appearance of the epithelial cells can vary and different degrees of atypia may be seen. A variant is atypical lobular hyperplasia which is characterised by hyperplasia of the terminal duct and acini; this has some of the features of lobular carcinoma in situ (LCIS). The importance of this lies in the increased risk of the subsequent development of breast cancer (see later).

Fibrosis (sclerosis)

There is a substantial increase in the content of dense fibrous tissue, with loss of elastic tissue, fat and epithelial elements.

Cyst formation

Numerous cysts (macro or micro) may also develop and this is discussed in more detail in the appropriate section above.

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