Challenges and potential pitfalls in magnetic resonance imaging of more elusive breast carcinomas.

Breast cancer is a heterogeneous group of diseases caused by differences in the biological, clinical, radiologic, and pathologic features of the different types of invasive carcinoma in the breast. The majority of invasive breast carcinomas are the invasive ductal or no special-type (NST) carcinomas. The rest of the invasive carcinomas are either nonductal carcinoma subtypes or special-type carcinomas, making up 20%-30% of all invasive carcinomas. The latter group comprises very different and distinctive types of cancer with imaging characteristics and challenges that are unique to each subtype. The invasive lobular carcinoma is the most common type of the nonductal carcinomas and can be difficult to detect on imaging because of the distinct pattern of tumor growth in sheets of single file cells with minimal desmoplastic reaction. The mucinous carcinoma of the breast contains extracellular mucin, secreted by the tumor cells. The mucin within these tumors result in imaging features that overlap with benign breast lesions, and may lead to misdiagnosis. Other rare and aggressive breast cancers include metaplastic breast carcinoma and inflammatory breast carcinoma. Both diseases have a poorer prognosis than invasive ductal carcinoma. This article will focus on the rarer non-NST carcinoma of the breast that can be a challenge to assess with imaging, partially related to the unique biology of these cancers.