## Investigation of Choice: Core Needle Biopsy **Key Point:** Core needle biopsy (CNB) under ultrasound or stereotactic guidance is the gold standard for histological diagnosis of suspicious breast lesions before definitive surgical management. ### Why Core Needle Biopsy? **High-Yield:** CNB provides: - Tissue diagnosis (histology, not just cytology) - Allows assessment of grade and hormone receptor status - Guides surgical planning (lumpectomy vs. mastectomy) - 90–95% sensitivity and specificity for malignancy - Minimally invasive with low morbidity - Can be performed as an outpatient procedure ### Comparison of Diagnostic Modalities | Investigation | Tissue Type | Diagnostic Accuracy | Role in Breast Cancer | |---|---|---|---| | **Core Needle Biopsy** | Histology | 90–95% | Gold standard for diagnosis | | Fine Needle Aspiration | Cytology | 65–80% | Not recommended for breast cancer | | Excision Biopsy | Histology | 100% | Therapeutic + diagnostic (reserved for benign lesions or after CNB) | | MRI Breast | Imaging | 90% sensitivity, 72% specificity | Staging, not diagnosis; used after diagnosis confirmed | **Clinical Pearl:** Excision biopsy should NOT be the first diagnostic step because it commits the patient to surgery before tissue diagnosis is confirmed, and it may compromise surgical margins if malignancy is found. **Warning:** Fine needle aspiration cytology (FNAC) has poor sensitivity in breast cancer and is not recommended for diagnostic confirmation. It is operator-dependent and cannot assess histological grade or receptor status. **Mnemonic — CNB Advantages: TISSUE** - **T**issue diagnosis (histology) - **I**maging-guided (ultrasound/stereotactic) - **S**ensitivity high (90–95%) - **S**uitable for outpatient - **U**nderstanding grade & receptors - **E**xcision avoided before diagnosis 
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