Microglandular adenosis or microglandular adenoma? A molecular genetic analysis of a case associated with atypia and invasive carcinoma

The Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, UK.
Histopathology (Impact Factor: 3.45). 11/2009; 55(6):732-43. DOI: 10.1111/j.1365-2559.2009.03432.x
Source: PubMed


Microglandular adenosis (MGA) is a rare breast lesion, which has long been considered to be hyperplastic. However, atypical forms of MGA (AMGA) and invasive carcinomas arising in the background of MGA are recorded. Recent studies have suggested that MGA may be a non-obligate precursor of invasive carcinomas that are negative for hormone receptors and lack HER-2 overexpression (triple-negative phenotype). The aim of this study was to determine whether MGA is clonal and whether it harbours chromosomal aberrations similar to those found in matched invasive ductal carcinoma of no special type (IDC-NST).
We report on a case comprising MGA, AMGA and a high-grade IDC-NST. The three components were separately microdissected and subjected to genetic analysis with high-resolution microarray comparative genomic hybridisation. Identical genetic changes were detected in all components with subsequent acquisition of additional genetic aberrations in the invasive component, suggesting that MGA was the substrate for the development of the invasive carcinoma. Immunohistochemistry revealed concordant profiles across all components, characterized by triple-negative phenotype and variable positivity for basal markers.
Similar to adenomas, MGA is, at least in some cases, a clonal lesion and may be a non-obligate precursor of a subgroup of high-grade triple-negative and basal-like breast carcinomas.

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    • "Histologically, MGA is characterized by a haphazard infiltration of small, uniformly open, and round glands in dense, hypocellular, and fibrous tissue, or fatty mammary stroma [3,4]. The glands are lined by a monolayer of flat to cuboidal epithelial cells that lack a myoepithelial layer (Figure 3) [2], which can be verified by immunohistochemistry. MGA immunohistochemistry is positive for pancytokeratin and negative for smooth muscle actin (Figures 5, 6), so the lesion is often confused with a tubular carcinoma. "
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    ABSTRACT: Microglandular adenosis (MGA) of the breast is a very rare and benign proliferative lesion. Most patients complain of a palpable breast mass that may arouse a clinical suspicion of breast cancer. Histopathologically, it is hard to distinguish MGA from breast cancer because of the lack of a myoepithelial layer and infiltrative proliferation. Several studies have reported a strong relationship between MGA and carcinoma arising in MGA, so the mass should be excised completely in cases of MGA determined from a core needle biopsy rather than observation. A 72-years-old woman presented with a palpable breast mass. On physical examination, a mass was palpable in the right upper outer quadrant area and somewhat fixed to the surrounding tissues and pectoralis major muscle. We could not detect any mass or dense lesion on mammography because of a grade 4 dense breast. Ultrasonographic findings revealed a low echoic lesion with indistinct margins. The result of a core needle biopsy was MGA, which was confirmed by excision. We report one case of MGA, which was believed to breast cancer clinically.
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