Fibromatosis-Like Metaplastic Breast Carcinoma Mimicking IgG4-Related Sclerosing Mastitis: a Case Report

Fibromatosis-like metaplastic breast carcinoma is an uncommon variety of breast cancer whose diagnosis could be challenging. The reported case underlines the diagnostic difficulties if abundant inflammatory cells and no in situ carcinoma or epithelioid features are present in the sample. The broad spectrum of differential diagnosis, including benign and malignant lesions, requires immunohistochemical characterization. Cytokeratin expression is mandatory. The case clearly represents the indolent behavior of this entity whose treatment algorithm differs from that of all other breast cancers. As a curative treatment, our patient was offered a multi-modal approach, which cannot be considered a standard option for other triple-negative breast cancers. The overall benefit in disease-free survival was surprisingly strong, despite some prognostic negative markers, such as Ki67 index and p53 nuclear accumulation. The presence of tumor infiltrating lymphocytes opens a width of novel therapeutic options that are yet to be assessed in this subgroup of breast cancers.