Low-grade adenosquamous carcinoma of the breast

Low-grade adenosquamous carcinoma is a rare and unique form of invasive mammary carcinoma. Though it is categorised as a variant of metaplastic carcinoma, it differs from its counterparts in this heterogeneous category by its relative clinical indolence, also reflected histologically in its low-grade cytomorphology. Descriptions of such a tumour were reported as early as 1912. However, low-grade adenosquamous carcinoma was only formally recognised in 1987 with the publication of Rosen and Ernsberger's landmark paper. Since then, several case reports and larger series have reaffirmed the clinicopathological characteristics of this unusual and uncommon tumour. Due to its rarity, however, many aspects of low-grade adenosquamous carcinoma, including its immunohistochemical and genetic profiles, remain unclear. This paper reviews the literature on this entity from 1987 to date, summarising its clinical and pathological features, and highlighting the diagnostic challenges it poses.