Gynecomastia

Definition

Increased ducts and prominent stroma
May be well or poorly circumscribed
Early phase
- Intraductal epithelial proliferation
  - Both epithelial and myoepithelial
  - May be micropapillary or cribriform
  - May be atypical
    - No evidence of increased risk of carcinoma
    - No studies have examined the significance of atypical hyperplasia and carcinoma in situ in gynecomastia
      - In the absence of such studies we use those derived for the female breast
  - May show squamous metaplasia
  - Apocrine metaplasia frequent
- Periductal stroma typically edematous
  - May show increased cellularity
Late phase
- Less epithelial proliferation
  - May be atrophic with dilated ducts
- Periductal fibrosis
Lobule formation infrequently seen
Occasional periductal lympho-plasmacytic infiltrate
Pseudoangiomatous stromal hyperplasia in about 25% of cases
Histology independent of cause