Mucinous lesions

Mucinous breast lesions refer to a broad spectrum of entities, ranging from benign fibrocystic changes with luminal mucin to mucocele-like lesions, invasive mucinous carcinoma, and cystadenocarcinoma mucinous (Tan et al., J Clin Pathol 61(1):11-19, 2008). There are also lesions with stromal mucinous or myxoid material that mimic the more conventional "mucinous" entities. Mucins are complex carbohydrates secreted by specialized epithelial and occasionally by connective tissue cells. "Mucoid" and "myxoid" are traditionally used to refer to extracellular mucosubstances of epithelial and mesenchymal origins, respectively. Apart from lesions associated with extracellular mucin, lobular neoplasia, DCIS, and infiltrative lobular carcinomas can demonstrate intracytoplasmic mucin. Stromal myxoid changes can be observed in fibroadenomas and phyllodes tumors, as well as in the less common lesions of pleomorphic adenoma (Tse et al., Fine needle aspiration cytology of the breast. Springer, Berlin; Heidelberg, 2013). Since the fifth edition of the WHO Breast Tumors Classification, it is now perceived that some invasive lobular carcinomas are associated with extracellular mucin production, an extremely rare feature.