On histopathology,<unk>  is characterized by groups of tumor cells with syncytial appearance (that is, seemingly fused cytoplasms, at left). There is typically also a lymphocytic and plasma cell infiltrate (right). Criteria must be met through the Ridolfi criteria. Although there are other classifications for diagnosis, the Ridolfi criteria are the most commonly used. There must be histologic evidence of lymphoplasmacytic infiltration, noninvasive microscopic circumscription, greater than 75% syncytial growth pattern, and high-grade nuclei. It is immunologically typically triple-negative, with negative estrogen receptors (ER), negative progesterone receptors (PR), and negative HER2/neu receptors. There are also<unk> s that are found to be estrogen receptors (ER) and/or progesterone receptor (PR) positive, making diagnosis less straightforward. Ridolfi Criteria 1. Lymphoplasmacytic infiltration 2. Noninvasive microscopic circumscription 3. >75% syncytial growth pattern 4. High-grade nuclei
Medullary breast carcinoma
Mucinous carcinoma of the breast
Adenomyoepithelioma of the breast
Paget's disease of the breast
Hereditary lobular breast cancer
Inflammatory breast cancer
Apocrine gland carcinoma
Bartholin gland carcinoma