Blunt duct adenosis: a separate entity from columnar cell lesions?

Blunt duct adenosis (BDA) is a breast lesion first described by Foote and Stewart in 1945 as a proliferative benign lesion of the terminal duct lobular unit. Throughout recent decades, further literature descriptions of BDA have been confusing. Some consider BDA to be a separate entity, some a growth pattern of columnar cell changes. The WHO 2012 considered BDA and columnar cell changes to be synonyms, while columnar cell lesions, especially those with atypia, are part of a spectrum of early precursors of the low nuclear grade breast neoplasia family. In the updated WHO 2019 version, BDA is mentioned as ‘not recommended’ terminology for columnar cell lesions without further discussing it, leaving the question open if BDA should be considered a separate entity.Good diagnostic criteria for BDA have however largely been lacking, and its biological background has not yet been unravelled. In this paper, we point out that BDA is mainly associated with benign breast lesions and not with other recognised precursor lesions. Further, 16q loss, which is the hallmark molecular event in the low nuclear grade breast neoplasia family, is lacking in BDA. We therefore hypothesise that BDA may not be a true precursor lesion but a benign polyclonal lesion, and propose morphological diagnostic criteria to better differentiate it from columnar cell lesions.

Circumscribed Mass: Fibroadenoma

A fibroadenoma is a benign fibroepithelial breast tumor arising from the terminal duct-lobular unit (TDLU), composed of epithelial and stromal elements. The overwhelming majority of fibroadenomas present as palpable or imaging-detected circumscribed masses showing sharp demarcation between the lesion and the adjacent breast tissue. Fibroadenomas are the most common benign breast tumor occurring in women, with a peak incidence in the third and fourth decades, but they can occur from childhood through the eight decade of life. This chapter, appearing in the section on asymmetry, mass, and distortion, reviews the key clinical and imaging features, differential diagnosis, and management recommendations for fibroadenomas.

Circumscribed Mass: Cysts, Complicated Cysts, Clustered Microcysts

Benign cysts can occur in women of all ages, but they have a predilection for women in their 40s and 50s, and are far less common in younger and older women. Most cysts arise at the level of the terminal duct-lobular unit (TDLU); less commonly, cysts are caused by ectasia of central ducts. This chapter, appearing in the section on circumscribed mass, reviews the key clinical and imaging features, differential diagnosis, and management recommendations for primary cystic masses, including simple cysts, complicated cysts, and clustered microcysts. Careful assessment of sonographic features usually allows a definitive diagnosis of these benign entities that do not typically require tissue sampling. Some complex masses containing fluid and/or cystic-appearing components may require tissue sampling for diagnosis.