Atypical Lobular Hyperplasia of the Breast

Definition

A proliferative lobular process that exhibits cytologic features of lobular carcinoma in situ but does not fulfil the requirements for extent of involvement

Same cytologic features as LCIS
- May be classic or pleomorphic
  - Classic: uniform, small, round, discohesive cells, has been subdivided as:
    - Type A - small completely bland cells
    - Type B - slightly larger, slightly irregular, small nucleoli
  - Pleomorphic: larger, sometimes irregular nuclei, often with prominent nucleoli
- May exhibit pagetoid spread into ducts
No lobular unit completely fulfils the extent of involvement required for LCIS
- No lobular units show complete filling of all the acini, OR
- Even if all filled, fewer than half of the acini in the lobule expanded
There is no category of non-atypical lobular hyperplasia

Richard L Kempson MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Original posting:: May 1, 2006