Microglandular Adenosis and Associated Invasive Carcinoma

Abstract

Context.— Microglandular adenosis is a rare borderline neoplastic lesion of the breast composed of haphazardly located small, round tubules with a single cell layer interspersed within breast stroma and/or adipose tissue. Microglandular adenosis is devoid of a myoepithelial cell layer, and has a characteristic immunophenotype, being positive for S100 and negative for estrogen receptor, progesterone receptor, and HER2/ neu. When associated with cancer, microglandular adenosis and associated invasive carcinoma share the same molecular alterations, including TP53 mutation; therefore, microglandular adenosis is considered a nonobligate precursor of triple (HER2/ neu, estrogen and progesterone receptors)–negative breast carcinoma. Microglandular adenosis is an important diagnostic pitfall as it can be easily mistaken for a low-grade invasive carcinoma. Objective.— To provide a review of the clinicopathologic features of microglandular adenosis and associated invasive carcinoma, with emphasis on key features separating entities in the differential diagnosis. Data Sources.— Review of current literature on microglandular adenosis and associated invasive carcinoma and personal experience of authors. Conclusions.— Microglandular adenosis can mimic breast carcinoma; attention to key features, including morphologic-immunophenotypic correlation, is essential in establishing the diagnosis.

Chromosome 2q gain and epigenetic silencing of GATA3 in microglandular adenosis of the breast

“…Initially, it was considered a benign tumor or reactive epithelial change [1,2]. A small number of clinical and molecular studies on MGA has been published since its first description [2][3][4][5][6][7][8][9][10][11][12], and the biology of MGA is still little known [6]. The current study confirms and extends previous findings on the molecular pathology of MGA.…”

“…Furthermore, MGA lacks a myoepithelial cell layer surrounding the haphazardly spread tubules. Accordingly, MGA is also negative for myoepithelial or basal differentiation markers, including CK5/6 and p63 [3,5]. Strong immunoreactivity for S100 remains a key diagnostic feature, and this feature was discovered as an empirical finding [3].…”

“…MGA may present as a mass-forming, palpable tumor or as an incidental microscopic finding in breast biopsies [2]. Histologically, it is characterized by small, round tubules haphazardly spread in the mammary fat tissue, without desmoplastic reaction [2][3][4][5][6]. Nuclear atypia is absent or mild, as is mitotic activity.…”

“…Immunohistochemically, MGA shows a peculiar phenotype characterized by the absence of estrogen receptor (ER) and progesterone receptor (PR) expression but positive staining for S100 [3]. MGA also lacks overexpression of HER2 and is thus a triple-negative lesion [5]. Furthermore, MGA lacks a myoepithelial cell layer surrounding the haphazardly spread tubules.…”

“…In a subset of MGA cases, synchronous adjacent invasive BC may be encountered. These invasive BCs tend to share some morphological features with MGA, such as cytoplasmic clearing and a triple-negative immunophenotype [5]. Cases of MGA with more pronounced nuclear atypia (occasionally termed atypical MGA, aMGA) may represent lesions in transition from MGA to BC [3].…”