## Most Common Histological Type of Breast Cancer **Key Point:** Invasive ductal carcinoma of no special type (IDC-NST) is the most common histological subtype of breast cancer, accounting for 70–80% of all invasive breast cancers. ### Frequency of Breast Cancer Histological Types | Histological Type | Frequency (%) | |-------------------|---------------| | IDC-NST | 70–80 | | Invasive lobular carcinoma | 10–15 | | Tubular carcinoma | 2–5 | | Mucinous (colloid) carcinoma | 1–3 | | Medullary carcinoma | 1–2 | ### Characteristics of IDC-NST - **Definition:** Invasive carcinoma lacking specific differentiation features - **Prognosis:** Intermediate; varies widely based on grade (Nottingham/Bloom-Richardson) - **Grade-dependent:** Grade I (favorable), Grade II (intermediate), Grade III (poor) - **Staging:** TNM staging applies uniformly across all histological types **Clinical Pearl:** IDC-NST is a diagnosis of exclusion; specific types (tubular, mucinous, medullary) are identified only when they meet strict morphological criteria. **High-Yield:** Histological type and grade are independent prognostic factors; grade is more predictive of outcome than type alone.
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