What are the different types of breast cancer?

Types of Breast Cancer

Breast cancer is primarily classified based on its origin within the breast tissue, with approximately 85-90% of invasive carcinomas being ductal in origin, while the remaining types include various special histological subtypes that have distinct clinical behaviors and prognoses. 1

Major Classifications of Breast Cancer

Based on Invasiveness:

1. Non-invasive (In Situ) Carcinomas

   • Ductal Carcinoma In Situ (DCIS): Abnormal cells contained within the milk ducts
   • Lobular Carcinoma In Situ (LCIS): Abnormal cells within the lobules; considered a risk factor rather than true cancer 1

2. Invasive Carcinomas

   • Invasive Ductal Carcinoma (IDC): Most common type (70-75% of all breast cancers) 2
   • Invasive Lobular Carcinoma (ILC): Originates in the milk-producing glands

Special Histological Types of Invasive Breast Cancer:

• Mucinous (Colloid) Carcinoma: Characterized by mucin production, typically has favorable prognosis 1
• Tubular Carcinoma: Well-differentiated carcinoma with tubule formation, excellent prognosis 1
• Adenoid Cystic Carcinoma: Rare type with excellent prognosis despite often being triple-negative 3
• Medullary Carcinoma: Characterized by prominent lymphocytic infiltration 3
• Metaplastic Carcinoma: Contains mixed epithelial and mesenchymal components 3
• Micropapillary Carcinoma: Aggressive variant with high lymph node involvement 3
• Neuroendocrine Carcinoma: Shows neuroendocrine differentiation 3
• Apocrine Carcinoma: Characterized by apocrine differentiation 3
• Inflammatory Breast Cancer: Not a histological subtype but a clinical presentation with skin changes and rapid progression 1

Molecular Classification

Modern breast cancer classification incorporates molecular features that significantly impact treatment decisions and prognosis:

1. Luminal A: ER+/PR+, HER2-, low Ki-67
2. Luminal B: ER+/PR+, HER2+ or HER2- with high Ki-67
3. HER2-enriched: ER-, PR-, HER2+
4. Triple-negative/Basal-like: ER-, PR-, HER2- 4

Emerging Classification Systems

Recent research suggests more anatomically precise classification systems:

• Ductal Adenocarcinoma of the Breast (DAB): Originates from major lactiferous ducts, characterized by neoductgenesis and often more aggressive behavior 5
• Acinar Adenocarcinoma of the Breast (AAB): Originates from terminal ductal lobular units (TDLUs), appears as stellate/spiculated or circular/oval masses on mammography 6

Clinical Implications of Breast Cancer Types

Different types of breast cancer have varying clinical behaviors:

• Invasive ductal carcinoma variants like tubular, mucinous, and adenoid cystic carcinomas typically have more favorable natural histories 1
• Special histological types are generally more homogeneous in their molecular profiles compared to IDC-NOS (not otherwise specified) 3
• Molecular subtypes strongly influence treatment decisions, with different approaches for hormone receptor-positive, HER2-positive, and triple-negative disease 4

Important Diagnostic Considerations

Accurate pathological assessment is critical for proper classification:

• Core needle biopsy is essential for confirming diagnosis before treatment 2
• Comprehensive pathology reporting should include tumor size, grade, hormone receptor status (ER/PR), HER2 status, and lymph node involvement 1
• Molecular testing may include gene expression profiling to further refine classification and treatment planning 4

Understanding the specific type of breast cancer is crucial for determining appropriate treatment strategies and predicting outcomes, as different subtypes respond differently to various therapeutic approaches.