Xanthomatous pseudotumor. An unusual postchemotherapy phenomenon in breast cancer.

Neoadjuvant chemotherapy has become an integral part of the treatment for locally advanced breast cancer. It facilitates tumor resectability and also provides an opportunity for the assessment of therapeutic response and prognosis. We report a case in which a large primary breast carcinoma was significantly reduced in size clinically and replaced by a mass lesion that was composed almost entirely of foamy histiocytes. This peculiar phenomenon is described in detail, together with a brief review of the other known postchemotherapy histologic features that include tumor necrosis, tumor cell cytoplasmic vacuolation and marked nuclear atypia, accompanying chronic inflammatory cellular infiltrate, fibrosis, and ductal-lobular atrophy.