Definition
A proliferative lobular process that exhibits cytologic features of lobular carcinoma in situ but does not fulfil the requirements for extent of involvement
Alternate / historical names
Diagnostic Criteria
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
