Pseudoangiomatous Stromal Hyperplasia

**Semantic type:** Disease or Syndrome

**Definition:** A benign proliferation of the stromal cells in the breast. It is classified as simple, when associated with the presence of slit-like spaces without erythrocytes and as fascicular/proliferative, when spindle cell proliferation without atypia is present. It is often seen in breast tissue specimens as small foci associated with benign epithelial lesions. Pseudoangiomatous stromal hyperplasia presenting as a well-circumscribed palpable mass is rare.

**Synonyms:** - Breast Pseudoangiomatous Stromal Hyperplasia - PASH