A 55-year-old woman has a breast mass. Core biopsy shows infiltrating carcinoma with positive ER/PR and HER2 overexpression (3+ IHC, FISH amplified). According to molecular classification, this tumour belongs to:
- A Luminal A subtype
- B HER2-enriched (ER-/PR-/HER2+) subtype
- C Luminal B subtype (HER2-enriched) ✓
- D Triple-negative/basal-like subtype
Correct answer: C. Luminal B subtype (HER2-enriched)
Explanation
The molecular subtypes of breast cancer are defined by ER, PR, HER2, and Ki-67 status. Luminal B includes ER-positive tumours that are either HER2-positive (regardless of Ki-67) or HER2-negative with high Ki-67 (>20%). This patient's ER+/PR+/HER2+ tumour falls into Luminal B HER2-positive, which has worse prognosis than Luminal A (ER+/PR+/HER2−/low Ki-67) and requires both endocrine therapy and anti-HER2 therapy. HER2-enriched subtype is ER−/PR−/HER2+; triple-negative is ER−/PR−/HER2−.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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