## Histological Classification of Invasive Breast Carcinoma **Key Point:** Invasive Ductal Carcinoma (IDC), also called Invasive Carcinoma of No Special Type (NST), accounts for approximately 70–80% of all invasive breast cancers and is the most common type encountered in clinical practice. ### Frequency Distribution | Histological Type | Frequency | Prognosis | |---|---|---| | Invasive Ductal Carcinoma (NST) | 70–80% | Intermediate | | Invasive Lobular Carcinoma | 10–15% | Similar to IDC | | Tubular Carcinoma | 5–10% | Favorable | | Mucinous (Colloid) Carcinoma | 2–3% | Favorable | | Medullary Carcinoma | 1–2% | Intermediate | | Papillary Carcinoma | <1% | Favorable | **High-Yield:** IDC is the default diagnosis when a breast carcinoma lacks specific differentiating features. It presents as a hard, infiltrative mass with poor prognosis compared to special types like tubular or mucinous carcinomas. **Clinical Pearl:** Special histological types (tubular, mucinous, medullary) often have better prognosis than IDC despite similar grade, making histological classification important for prognostication beyond grade and stage alone. ### Why Other Types Are Less Common - **Invasive Lobular Carcinoma (ILC):** Second most common (~10–15%), but still significantly less frequent than IDC. ILC tends to be multifocal and bilateral more often than IDC. - **Mucinous & Medullary:** Rare special types (<3% each) with distinct morphology and better prognosis. [cite:Robbins 10e Ch 24]
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