An infiltrating breast carcinoma with a relatively favorable prognosis. It is an uncommon carcinoma, accounting for less than 1% of all infiltrating breast carcinomas. It is well circumscribed, with soft cut surface and often of considerable size. Microscopically, the predominant growth pattern is syncytial with broad anastomosing bands or sheets of malignant cells. The malignant cells are round with abundant cytoplasm and vesicular nuclei. The sheets of malignant cells are associated with a marked lymphoplasmacytic infiltrate. Glandular or tubular structures are absent. [from
NCI]