General
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• Low power diagnosis of increase in glandular elements plus stromal proliferation that distorts and compresses glands
• Preservation of luminal epithelium and peripheral myoepithelium with surrounding basement membrane

Terminology
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• Adenosis tumor / nodular adenosis:
  • Palpable mass (AJR Am J Roentgenol 2000;175:31)
  • Coalescent foci of typical sclerosing adenosis
• Myoepitheliosis:
  • Rare; sclerosing adenosis with predominance of myoepithelial cells, presents as multifocal microscopic lesions (Am J Surg Pathol 1991;15:554)
  • Cells may have longitudinal nuclear grooves

Epidemiology
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• Mean age 30 years
• Found in 12-28% of all benign and 5-7% of malignant biopsies (J Ultrasound Med 2013;32:2029)

Clinical features
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• As a single feature, increased risk of cancer of 1.5 to 2x (Cancer 1989;64:1977)
• Does not provide further risk stratification in the presence of other proliferative disease / atypical hyperplasias (Breast Cancer Res Treat 2014;144:205)
• Rarely involved by LCIS and mistaken for invasive carcinoma (Mod Pathol 1991;4:31)
• DCIS arising in sclerosing adenosis has a higher frequency of bilaterality (Clin Breast Cancer 2012;12:398, Breast Cancer 2014;21:732)
• Can mimic malignancy clinically and radiologically

Radiology
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• Circumscribed to spiculated mass with architectural distortion
• Amorphous or pleomorphic clustered microcalcifications

Case reports
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• 82 year old woman with sclerosing adenosis in sentinel axillary lymph nodes (Arch Pathol Lab Med 2008;132:1439)

Treatment
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• The presence of sclerosing adenosis alone in a core biopsy does not require surgical excision

Gross description
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• Multinodular, cuts with increased resistance
• Gritty but no chalky yellow-white foci or streaks

Micro description
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• Low power diagnosis; increase in glandular elements plus stromal proliferation that distorts and compresses glands
• Maintains lobular architecture at low power with rounded and well defined nodules
• Centrally is more cellular with distorted and compressed ductules; peripherally has more dilated ductules
• Often microcalcifications, apocrine metaplasia
• Two cell layers are present, but myoepithelial cells may vary from being prominent to indistinct
• Also intralobular fibrosis, elastosis and apocrine metaplasia; florid changes are associated with pregnancy
• Rarely penetrates walls of veins or perineural spaces
• No necrosis, no pleomorphism
• Epithelium may be involved by proliferative / atypical lesions or in situ carcinoma
• Can mimic malignancy:
  • If non-lobulocentric / infiltrative into fat or stroma
  • Conspicuous myoepithelial cells with attenuated epithelial cells can appear like stands of single cells and mimic invasive lobular carcinoma
  • Atypical apocrine metaplasia: nuclear atypia / rare mitosis (Mod Pathol 1991;4:1)
  • Perineural invasion

Micro images
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Low power

 

Small ducts with microcalcifications

High power

Late stage; fibrosis and decreasing acini

Resembles microglandular adenosis

Myoid differentiation

     

Sclerosing adenosis at core biopsy in a 40 year old pregnant woman

     

Various images

Adenosis tumor

In sentinel nodes

AFIP Fig 52: ducts dilated at periphery

 

Fig 56-57: Small ducts with microcalcifications

Fig 70: Normal glands in upper right

Fig 58: Retention of myoepithalial-type cells but loss of ductal epithelium

Fig 59: Small bland ducts adjacent to nerve

 

Fig 53, 55: Intraductal papilloma

Fig 54: Invagination into cystic duct

   

Fig 194, 195, 197: With LCIS

 

Fig 198, 199: With LCIS and microinvasion (arrows)

 

SMM-HC

Smooth muscle actin

 

CK14

Cytology description
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• Moderate to markedly cellular, with small to large groups of benign epithelial cells in acinar sheets / cohesive groups / tubules and scattered individual epithelial cells
• Also small foci of dense hyalinized stroma (Acta Cytol 2001;45:353, Diagn Cytopathol 2008;36:496)
• Tubules may have an angular configuration (Am J Clin Pathol 2012;138:96)

Positive stains
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• Myoepithelial cells: smooth muscle actin, p63, calponin, HHF35, CK 5/6
• Basement membrane (surrounds tubules): laminin and type IV collagen

Differential diagnosis
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• Invasive ductal carcinoma: not lobular at low power, cells have marked atypia, no myoepithelial cells

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