Periductal Stromal Tumor of the Breast with a Promoter Mutation: First Case Report with Comprehensive Molecular Analysis.

The molecular pathogenesis of breast fibroepithelial tumors continues to be elucidated. Recently, highly recurrent mutations arising in exon 2 at codon 44 were discovered in fibroadenomas and phyllodes tumors. In addition, a high prevalence of promoter mutations in two hotspots (124 and 126 bp upstream from the translation start site) was discovered in up to 65% of phyllodes tumors. Breast periductal stromal tumors are a potentially distinct category of fibroepithelial lesions that are exceptionally rare with controversial classification and pathogenesis. Herein, we report the first comprehensive molecular genetic workup of a breast periductal stromal tumor that harbored a promoter -124C > T mutation, supporting a relation to phyllodes tumors.