Epithelial breast tumors spectrum

Overview and classification

Based on World Health Organization (WHO) Classification of Tumours of the Breast (5th edition, 2019). Spectrum ranges from benign proliferation to invasive carcinoma.

• Key Concept: The "Terminal Ductal Lobular Unit" (TDLU) is the origin of most epithelial neoplasms.
• Molecular Classification: High exam relevance for prognosis and adjuvant therapy decisions.
  • Luminal A: ER+/PR+, HER2-, low Ki-67 (slow growth).
  • Luminal B: ER+/PR+, HER2 +/- (often +), high Ki-67.
  • HER2-enriched: ER-/PR-, HER2+.
  • Basal-like (Triple Negative): ER-/PR-/HER2-; associated with BRCA1.

Spectrum

Benign epithelial lesions

• Intraductal papilloma

Precursor lesions

• Atypical ductal hyperplasia
• Lobular neoplasia
• Ductal carcinoma in situ

Invasive carcinomas

• Invasive carcinoma of no special type
• Invasive lobular carcinoma
• Tubular carcinoma
• Mucinous carcinoma
• Papillary carcinoma

Staging and reporting (TNM 8)

• T Stage (Primary Tumor):
  • Tx: Cannot be assessed.
  • Tis: Carcinoma in situ (DCIS, Paget's). Note: LCIS is no longer staged as Tis in AJCC 8th ed, but remains a risk factor.
  • T1: ≤ 20 mm. (T1a: 1-5mm, T1b: 5-10mm, T1c: 10-20mm).
  • T2: > 20 mm but ≤ 50 mm.
  • T3: > 50 mm.
  • T4: Direct extension to chest wall (T4a), skin ulceration/nodules/edema (T4b), both (T4c), or Inflammatory carcinoma (T4d).
• N Stage: Clinical (cN) vs Pathological (pN). Imaging plays key role in cN.
  • Level I: Lateral to pectoralis minor.
  • Level II: Posterior to pectoralis minor.
  • Level III: Medial to pectoralis minor (infraclavicular).
  • Supraclavicular: N3.
  • Internal Mammary: N2 (if solitary) or N3 (if with axillary nodes).

Management pathways (NICE Guidelines)

• Triple Assessment: Clinical exam + Imaging + Pathology (Core needle biopsy preferred over FNA for histology/receptor status).
• B3 Lesions (Uncertain malignant potential): e.g., ADH, ALH, Intraductal papilloma, Radial Scar.
  • Guideline: Vacuum-Assisted Excision (VAE) recommended to obtain larger sample and ensure no adjacent DCIS/invasion.
• Neoadjuvant Chemotherapy (NAC):
  • Indicated for T2+, N+, HER2+, or Triple Negative to downstage tumor.
  • Radiology Role: Clip placement in tumor and positive nodes PRIOR to NAC is mandatory for localization during surgery (Targeted Axillary Dissection - TAD).

High-yield exam trivia

1. Calcifications: Linear branching/casting = High grade DCIS.
2. Architectural Distortion: Always requires biopsy. Ddx: ILC, Radial Scar, Surgical scar.
3. T2 Bright Mass: Mucinous carcinoma, Fibroadenoma (myxoid), Necrotic IDC, Cyst.
4. Posterior Enhancement: Cyst, High-grade malignancy (Medullary/Triple neg), Abscess.
5. Multifocal vs Multicentric:
   • Multifocal: Same quadrant/ <5 cm apart (usually one resection).
   • Multicentric: Different quadrants / >5 cm apart (often requires mastectomy).