Pathology Associates Of Lexington, P.A.

Breast, Microglandular Adenosis (MGA)

Microglandular Adenosis

First described by McDivitt in 1968, there is concern that...especially when atypical...this lesion (MGA) represents a premalignant state^{1, 2}. Take great care to distinguish MGA (which should be excised) from ordinary adenosis [LMC-01-6487] and secretory adenosis (ordinary adenosis has ME cells, S100 neg. epithelials, and a lobulated pattern).

Banal, Ordinary MGA:
1. Treatment: excision with clear margin¹
2. Histology: almost always diffuse/disordered proliferation of small round tubular profiles...even into fat...with lumens containing PAS+ secretion, thickened BMs, each acinus distinctly circumscribable
3. Cytology: mitoses rare, fairly regular nuclei with inconspicuous/unapparent nucleoli
4. IHC¹:
  - epithelials are S100+²
  - ER, PR, and HER2 neg.
  - no ME cells
  - BM+ for laminin and/or type IV collagen
  - EMA neg. (tubular ca. always EMA+)
Atypical MGA:
1. Treatment: excision with "widely clear" margin¹
2. Histology: smaller lumens, and acinar budding & complexity and sharing of walls
3. Cytology: more atypia; more mitotic
4. IHC: same as banal MGA

References:

Rosen's Breast Pathology, text, 1997
Tavassoli seminar at MCG 21 April 2001, handout