Tubular Carcinoma of the Breast

Definition

A low grade breast carcinoma at least 90% of which is composed of well differentiated tubules

Stellate infiltrating configuration
- Fibrous arms radiate out
- Frequently infiltrates fat without a fibrous reaction
90% composed of small, minimally branched, oval to round ducts with gaping lumens
- Ducts frequently have pointed ends ("prows")
- Ducts lined by a single row of cells and are widely patent
- Apical snouts common
- Bridging by small columns of cells is OK
- Sheet-like stratification not seen
- Low grade cribriform carcinoma has same behavior so may constitute more than 10%
  - Report mixtures of these two simply as the predominant type
Nuclear grade I in at least 90% of cells
- Slightly enlarged cells
- Uniform nuclei, inconspicuous nucleoli, uniform chromatin
- Pleomorphism minimal or absent
- Mitotic figures unusual
- Remaining 10% must not show nuclear grade III
  - Behavior may be that of the high grade component
  - Report such tumors as mixtures of two types
95% are less than 2.0 cm diameter, most are less than 1 cm
Basement membrane absent by PAS and laminin stains and by EM
Myoepithelial cells absent on immunohistochemical stains