Breast, usual ductal hyperplasia

Benign epithelial hyperplasia of the breast can be florid, and fill/extend duct spaces. This can be difficult to distinguish from ductal carcinoma in situ. In this case, interpretation is more difficult because hyperplasia is present in a sclerosing lesion. However, the morphology is polymorphous (non-atypical), without the archictectural/structural changes of DCIS. Expression of CK5 is retained—a benign feature in this setting.