Infiltrating Lobular Carcinoma of the Breast

Definition

Infiltrating carcinoma typically composed of uniform cells often arranged in a linear infiltrative pattern

Classic type
- Uniform cells with grade I cytologic features
  - Signet ring differentiation may be prominent
  - Nuclear molding is often prominent
- Linear infiltrative pattern
  - Rows of cells no more than one or two cells wide
  - Frequent target-like concentric pattern around ducts
  - Poorly cohesive cells
- E-cadherin negative
Pleomorphic variant
- Larger, more atypical nuclei with grade II cytologic features
  - Must not be grade III
- Must have classic architectural pattern
Tubulolobular carcinoma is considered by some to be a variant of lobular carcinoma
Alveolar variant
- Classic grade I cytologic features
- Rounded groups of cells
Solid variant
- Classic grade I cytologic features
- Groups or trabeculae >2 cells thick infiltrate between collagen bundles
Signet ring variant
- Architectural and cytologic features of lobular carcinoma
- >20% signet ring differentiation
  - Mucin positive vacuoles