The most specific immunohistochemical marker to distinguish invasive lobular carcinoma from invasive ductal carcinoma of the breast is:
- A Loss of E-cadherin expression ✓
- B ER (estrogen receptor) positivity
- C HER2 overexpression
- D Ki-67 proliferation index above 20%
Correct answer: A. Loss of E-cadherin expression
Explanation
Invasive lobular carcinoma characteristically loses E-cadherin expression due to CDH1 gene mutations/silencing, causing the classic 'single file' or 'Indian file' infiltrating pattern without cohesive gland formation. ER positivity is common to both types. HER2 amplification is typically negative in lobular carcinoma. E-cadherin loss is the defining molecular and IHC difference.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.