General
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• Any hyperplastic process (see subtypes below) primarily involving glands (i.e. an increased number of glandular components)
• Common, benign, often accompanied by fibrosis

Terminology
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• Multiple types of adenosis are described:
  • Adenomyoepithelial adenosis
  • Apocrine adenosis
  • Microglandular adenosis
  • Sclerosing adenosis
  • Simple adenosis
  • Tubular adenosis
  • Blunt duct adenosis (now classified as columnar cell change)

Epidemiology
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• Premenopausal: lesions with predominant epithelial component (proliferation of acini and ducts); nodular adenosis
• Postmenopausal: lesions with more sclerosis (sclerosing adenosis)

Sites
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• Not specific

Etiology
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• Part of fibrocystic changes

Clinical features
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• Can present as a mass (as nodular adenosis or adenosis tumor) or as calcifications on imaging

Prognostic factors
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• With some types (sclerosing adenosis), the risk of subsequent breast cancer is 1.5-2x higher

Treatment
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• Does not require treatment if there is no cytologic atypia

Micro description
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• See also separate topics for each subtype
• Apocrine adenosis: adenosis with predominant apocrine cytology
• Microglandular adenosis: non lobulocentric proliferation of mammary glands with an infiltrative pattern, lined by a single epithelial layer with a basement membrane
• Sclerosing adenosis: lobulocentric proliferation of glands (2 layers) with glandular compression and distortion due to stromal proliferation
• Simple adenosis: loosely structured proliferation of acinar or tubular structures, with epithelial and myoepithelial layers, surrounded by basement membrane, without distortion of lobular architecture
• Tubular adenosis: haphazard proliferation of branching tubules (2 layers)

Micro images
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Blunt ductal - courtesy of Dr. Mark R. Wick

Columnar cell change - courtesy of Dr. Mark R. Wick

 

Nodular/Sclerosing - courtesy of Dr. Mark R. Wick

 

Sclerosing - courtesy of Dr. Mark R. Wick

Low power, somewhat lobular architecture

Enlarged lobules

Epithelial and myoepithelial cells

 

Adenosis with columnar cell change

Various images

Reticulin stain, continuous
basement membrane around
glands (AFIP)

Differential diagnosis
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• Invasive carcinoma: mainly an issue in cases of sclerosing, tubular and microglandular adenosis

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