Rapidly growing nodular pseudoangiomatous stromal hyperplasia of the breast in an 18-year-old girl.

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is a rare benign proliferation of mesenchymal stromal cells with irregular slit-like formations resembling angiomatous structures. In the majority of cases this lesion is a focal microscopic finding in breast biopsies performed for benign or malignant diseases. It may present in a pure diffuse or nodular form. The exact etiology and pathogenesis of this tumor-like lesion is still unknown, but a proliferative response of myofibroblasts to hormonal stimuli has been postulated. A large 12 x 9 x 3.5 cm rapidly growing nodular form of PASH of the breast in an 18-year-old woman is here described with clinical and histological findings. A possible hormonal etiology was indicated by elevated progesterone (three-fold) and decreased estrogen serum levels. Different diagnostic lesions, such as giant fibroadenoma and low-grade angiosarcoma, are discussed. To the authors' knowledge this is only the fourth case of nodular PASH of the breast reported in the English literature.