What is sclerosing adenosis?

Sclerosing Adenosis: Definition and Clinical Significance

Sclerosing adenosis is a benign proliferative breast lesion characterized by increased numbers of distorted lobular units (terminal ductal lobular units) accompanied by stromal fibrosis and sclerosis, creating a whorled pattern of compressed acini. 1, 2, 3

Pathologic Classification

Sclerosing adenosis is classified as a proliferative lesion without atypia in the benign breast disease spectrum. 1 This places it in an intermediate risk category, distinct from:

• Lower risk: Nonproliferative lesions (simple cysts, fibroadenomas, nonsclerosing adenosis) 1
• Higher risk: Proliferative lesions with atypia (atypical ductal hyperplasia, atypical lobular hyperplasia, LCIS) 1

Histologic Features

The defining microscopic characteristics include: 2, 3

• Lobulocentric proliferation involving both epithelial and mesenchymal (stromal) components 2
• Expanded lobular units with whorled, compressed acini creating a distorted architecture 4
• Stromal sclerosis and fibrosis that distorts the normal terminal ductal lobular unit structure 5, 3
• Preservation of the dual cell layer (myoepithelial and epithelial cells), which distinguishes it from invasive carcinoma 5

Clinical Context

Patient Demographics

Sclerosing adenosis typically affects: 2, 3, 4

• Perimenopausal women (most common age group) 2, 4
• Average age around 36-42 years in symptomatic cases 6
• Present in 27.8% of benign breast biopsies 3

Presentation

• Usually asymptomatic and discovered incidentally on screening mammography 2
• Occasionally presents as a palpable mass 2
• May be associated with calcifications on imaging 4

Breast Cancer Risk

Sclerosing adenosis approximately doubles the risk of subsequent invasive breast cancer, with a relative risk of 1.7-2.1. 3, 4

Risk Stratification Details

• SA alone (without atypia): Relative risk = 1.7-2.1 3, 4
• SA with coexistent atypical hyperplasia: Relative risk increases to 6.7 4
• Strong association with atypical lobular hyperplasia: ALH is present 2.7 times more frequently in biopsies with SA compared to other benign biopsies 4
• SA is present in 62.4% of proliferative disease without atypia and 55.1% of atypical hyperplasia cases 3

Important Caveat

While SA conveys increased risk as a single feature, it does not further stratify risk in women already diagnosed with other forms of proliferative breast disease (either with or without atypia). 3 The presence of proliferative disease or atypia supersedes the risk contribution of SA alone.

Diagnostic Challenges

Imaging Mimicry

Sclerosing adenosis lacks distinctive radiological features and frequently mimics malignancy on all imaging modalities. 2, 6

• Mammography: May appear as irregular mass or suspicious calcifications 2, 6
• Ultrasound: Can show suspicious features requiring further workup 2
• MRI: May demonstrate irregular masses or regional non-mass enhancement with increased vascularity 2
• Clinical examination, mammography, and ultrasound cannot reliably distinguish SA from breast cancer 6

Histologic Mimicry

When ductal carcinoma in situ (DCIS) occurs within sclerosing adenosis (SA-DCIS), it can closely mimic microinvasive or even invasive carcinoma. 5 This occurs because:

• The distorted architecture of SA can make intraductal carcinoma cells appear to be infiltrating the stroma 5
• Careful pathologic evaluation is essential to avoid overdiagnosis and overtreatment 5
• Immunohistochemical staining for myoepithelial markers can help confirm the benign architecture 5

Management Implications

Biopsy Requirement

Diagnostic biopsy is mandatory when sclerosing adenosis is suspected on imaging, as it cannot be reliably distinguished from carcinoma by imaging alone. 2, 6 Ultrasound-guided vacuum-assisted biopsy is commonly used. 2

Surveillance After Diagnosis

Following diagnosis of sclerosing adenosis without atypia: 1

• Routine annual screening mammography is appropriate (not shortened interval imaging) 1
• Studies show that 6-month follow-up imaging does not improve cancer detection rates compared to annual screening for proliferative lesions without atypia 1
• Consider the patient's overall breast cancer risk profile, including family history and breast density, when determining if supplemental screening is needed 1

Special Consideration

Patients with SA-DCIS may be at higher risk for bilateral breast cancer compared to those with DCIS alone, though this requires further study. 5