## Why Core needle biopsy under ultrasound guidance is right The structure marked **A** — an irregular, hypoechoic mass with spiculated margins — represents a BI-RADS 5 finding, which is defined as "highly suggestive of malignancy" with >95% likelihood of breast cancer (Rumack Diagnostic Ultrasound 5e, Ch 21). According to the BI-RADS classification and standard triple assessment protocol (Sabiston Textbook of Surgery 21e, Ch 35), BI-RADS 5 lesions mandate **immediate tissue diagnosis via biopsy**. Core needle biopsy (CNB) is the preferred approach because it provides architectural information, allows grading, and permits assessment of hormone receptor status (ER/PR) and HER2 status — all critical for treatment planning (endocrine therapy, HER2-targeted therapy, chemotherapy selection). This is the standard of care and cannot be deferred. ## Why each distractor is wrong - **Repeat ultrasound in 6 months**: BI-RADS 3 (probably benign, <2% malignancy) warrants 6-month follow-up. BI-RADS 5 is >95% malignant and requires immediate biopsy, not surveillance. Delaying diagnosis in a highly suspicious lesion is inappropriate and increases morbidity. - **Mammography followed by observation**: Mammography is part of the initial diagnostic workup but does not replace the need for biopsy in BI-RADS 5. Observation without tissue diagnosis is contraindicated when malignancy risk exceeds 95%. - **MRI for further characterization**: While MRI is valuable in specific contexts (BRCA carriers, dense breasts, staging), it is not the next step in a BI-RADS 5 lesion. MRI has high sensitivity but lower specificity and delays definitive diagnosis. Biopsy is the standard next step. **High-Yield:** BI-RADS 5 = >95% malignancy = biopsy (core needle preferred); BI-RADS 3 = <2% malignancy = 6-month follow-up. [cite: Rumack Diagnostic Ultrasound 5e Ch 21 (Breast); Sabiston Textbook of Surgery 21e Ch 35]
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