Invasive lobular carcinoma

Accounts for 5-15%. Cells lack E-cadherin (non-cohesive).

• Growth Pattern: "Indian file" (single file) infiltration; preserves architecture (little desmoplasia).
• Imaging Challenges:
  • Mammography: High false-negative rate. May present as subtle architectural distortion rather than a mass. "Shrinking breast" sign rare but classic.
  • US: Ill-defined area of shadowing without distinct mass.
  • MRI: Most sensitive modality. often non-mass enhancement.
• Metastasis Pattern: Peritoneum, retroperitoneum, GI tract, gynecologic organs (different from NST which favors lung/liver/bone).