B3 lesions of the breast

Definition

• B3 lesions are breast lesions of uncertain malignant potential: a heterogeneous group with a borderline histological spectrum and a variable but low risk of associated malignancy.

Classification

B classification

• B classification: The classification from B1 to B5 describes the assessment of malignancy potential of the core biopsy material, from normal tissue to malignancy.
• B3 lesions: B3 lesions with uncertain malignant potential include atypical ductal hyperplasia, flat epithelial atypia, lobular neoplasia, and papilloma.

• They include atypical ductal hyperplasia (ADH), flat epithelial atypia, classical lobular neoplasia, papillary lesions, benign phyllodes tumours and radial scars.
• If carcinoma is found in subsequent tissue, DCIS is categorised as B5a and invasive carcinoma as B5b.

Occurrence & epidemiology

Epidemiology

• Between 4 and 9% of all core needle biopsies are classified as B3, with numbers increasing due to MRI and vacuum-assisted biopsy; the positive predictive value for malignancy has fallen from 29 to 10%.
• Atypical hyperplasia (ADH and atypical lobular hyperplasia) is found in 4–10% of benign breast biopsies performed for imaging findings or palpable lesions.

Clinical features

• ADH is usually found incidentally on needle biopsy specimens obtained because of abnormal mammographic findings; flat epithelial atypia mostly appears as microcalcifications on mammography.

Histology

• Histologically ADH essentially resembles low-grade DCIS and is distinguished by extent: below 2 mm it is diagnosed as ADH, above 2 mm as low-grade DCIS.
• ADH increases breast cancer risk about fivefold; it is regarded as a risk lesion rather than a precursor lesion, because the associated carcinoma can arise anywhere in either breast and not only at the site of the ADH.

Diagnosis

• The diagnosis is made on core needle biopsy (mostly 14G) or vacuum-assisted biopsy (7G–11G) under ultrasound, stereotactic or MRI guidance.
• The rate of carcinoma in subsequent tissue varies by lesion; in the consensus conference data it was highest for ADH (27.6%) and considerably lower for papillary lesions (7.8%).

Keep learning in the app

Further reading (selection)

1. StatPearls: Atypical Ductal Hyperplasia (NCBI Bookshelf)
2. The Complex Path from Mammary Ductal Hyperplasia to Breast Cancer: Elevated Malignancy Risk in Atypical Forms (Biomedicines 2026, PubMed Central)
3. DocCheck Flexikon, Mammakarzinom

Cross-references