General
=========================================================================

• Rare lesion of haphazardly infiltrating, small, uniform, rounded, open glands with eosinophilic secretions
• Mimics invasive carcinoma due to irregularly distributed glands in fibrous or adipose tissue, lined by single layer of cells

Terminology
=========================================================================

• Also called microglandular hyperplasia

Clinical features
=========================================================================

• Can present as a palpable mass, usually a 3-4 cm ill-defined lesion
• Benign, although has been associated with carcinoma (Am J Surg Pathol 1986;10:237) in 27% of cases
  • Transition to invasive carcinoma (with immunohistochemical profile similar to microglandular adenosis) from atypical microglandular adenosis has been documented, although some cases may represent juxtaposition of 2 unrelated pathologies (Arch Pathol Lab Med 2007;131:1397)
  • May evolve into carcinoma (Int J Surg Pathol 2000;8:303, Am J Surg Pathol 2009;33:496), often adenoid cystic carcinoma (Am J Surg Pathol 2003;27:1052), also carcinomas with secretory and squamous differentiation (Rosen's Breast Pathology, 3rd Edition, 2009, 182-4)
  • Some cases are precursors of basal-like carcinoma (Histopathology 2009;55:732)

Radiology
=========================================================================

• Increased density or calcifications

Case reports
=========================================================================

• 73 year old woman with mammary carcinoma arising in microglandular adenosis (Arch Pathol Lab Med 2003;127:77)

Treatment
=========================================================================

• Complete excision to rule out invasion (Am J Surg Pathol 2008;32:544) and close followup, particularly if atypical features (Am J Surg Pathol 1983;7:137)
• May recur if incompletely excised
• Wide excision with documented negative margins is advised in atypical microglandular adenosis (Arch Pathol Lab Med 2007;131:1397)

Gross description
=========================================================================

• Palpable mass or small localized lesion
• Infiltrative and ill defined
• Usually 3-4 cm

Micro description
=========================================================================

• Haphazardly infiltrating collection of small, uniform, rounded, open glands with eosinophilic secretions, irregularly distributed in fibrous or adipose tissue
• Glands lined by single layer of cuboidal/flat cells with vacuolated/granular cytoplasm and bland nuclei
• No apocrine snouts, no nucleoli, no/variable myoepithelial layer, but thick basement membrane
• Atypical microglandular adenosis:
  • Pleomorphic glands and microacini
  • Budding glandular units and luminal bridging, mild cytologic atypia, prominent nucleoli, reduced intraluminal secretions, occasional mitotic figures
  • Intact basement membrane

Micro images
=========================================================================

Multilayered epithelium
with granular cytoplasm (AFIP)

 

Small round infiltrative glands (AFIP)

 

Haphazard glands apparently infiltrating stroma

Ducts lined by single cells
with secretory material

 

Smooth round glands

 

H&E and reticulin stain, courtesy of Dr. Mark R. Wick

 

Small uniform glands with open lumina

With ALH

 

With invasive and intraductal carcinoma

Fig 2: atypical
microglandular adenosis

Virtual slides
=========================================================================

Microglandular adenosis

With invasive ductal carcinoma

Cytology description
=========================================================================

• Sparse cellularity, monotonous population of medium sized cells with vacuolated clear cytoplasm, round and uniform nuclei, small nucleoli
• Also clear cells that are solitary or clustered with spindly fibroblasts (Diagn Cytopathol 1993;9:72)

Positive stains
=========================================================================

• CAM 5.2, AE1, S100 (Arch Pathol Lab Med 2007;131:1397), p63 (secretory epithelium, Histopathology 2005;47:611)
• CK8/CK18 and EGFR (Am J Surg Pathol 2008;32:544)
• PAS+ diastase resistant secretions
• Variable smooth muscle actin, vimentin, type IV collagen and laminin (around glands)

Negative stains
=========================================================================

• ER, PR, HER2 (triple negative)
• Actin, calponin, p63 (myoepithelial markers)
• EMA, GCDFP-15, p53, low Ki-67

Electron microscopy description
=========================================================================

• Thick basement membrane around epithelium; electron-lucent cytoplasm, sparse organelles (Am J Surg Pathol 1983;7:731)

Molecular / cytogenetics description
=========================================================================

• Clonal in some cases

Differential diagnosis
=========================================================================

• Apocrine adenosis: larger glands lined by luminal tall columnar cells with apocrine features and surrounded by flat myoepithelial cells
• Malignancy arising in microglandular adenosis:
  • In-situ carcinoma shows a solid proliferation of atypical cells (S100+) with preserved basement membrane
  • Invasive carcinoma cells form small closed tubules and cords with surrounding desmoplastic/myxoid stroma with or without a lymphocytic response
• Tubular carcinoma: stellate growth pattern, desmoplastic stroma, glands vary in size and shape with angulated "tear-drop" appearance; lined by cells with prominent apical snouts and without a surrounding basement membrane; EMA+, S100- (Arch Pathol Lab Med 2007;131:1397); ER+, PR+
• Well differentiated invasive ductal carcinoma with a microglandular adenosis pattern (Ann Diagn Pathol 2004;8:39); ER+, PR+

Additional references
=========================================================================

• Article by Drs. Joshi and Ahmad (May 2011), Stanford University - Microglandular Adenosis of the Breast

This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.

All information on this website is protected by copyright of PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions (click here for other contact information).