Is It Possible to Accurately Evaluate the Tumor Bed After Neoadjuvant Chemotherapy Using a 14G Tru-Cut Biopsy?

<b>Background/Objectives:</b> Accurately identifying residual disease in the breast following neoadjuvant systemic therapy (NST) is a critical aspect of treatment planning. While surgery remains the standard treatment, its omission may be considered in exceptional responders. However, this strategy is still under investigation and carries local and distant recurrence risks. No definitive method currently exists to confirm pathologic complete response (pCR) after NST. This study evaluates the reliability of ultrasound-guided 14G Tru-Cut biopsy in assessing post-NST disease status. <b>Methods</b>: Data from 204 breast cancer patients who underwent ultrasound-guided 14G Tru-Cut biopsy before surgery at Istanbul University Oncology Institute (March 2015-May 2024) were analyzed. Concordance between Tru-Cut biopsy and final pathology was assessed, along with diagnostic accuracy parameters, including false-negative rate (FNR), accuracy, negative predictive value (NPV), and positive predictive value (PPV). <b>Results:</b> The median patient age was 45 years (range: 26-86). The median initial tumor size was 32 mm, reducing to 10 mm post-treatment. Pathologic complete response (pCR) was 33.8% in surgical specimens and 40.7% in biopsy samples. Biopsy misdiagnosed 15 patients, with an overall FNR of 11.1% and accuracy of 92.2% (95% CI, 7.1-18.1%; 95% CI, 87.6-95.5%). Among patients with radiologic complete response (rCR) (n = 99), FNR was 25.8%, and accuracy was 92.1%. The best outcomes were in the rCR and Tru-Cut pCR subgroup, with an FNR of 5.9% and accuracy of 95.6%. In triple-negative breast cancer patients, FNR was 5%, and an accuracy was 97.4%. <b>Conclusions:</b> Although obtaining eight or more samples with a 14G Tru-Cut biopsy after NST is insufficient to alter clinical practice for detecting residual disease, the promising results observed in the rCR and Tru-Cut pCR subgroups suggest its potential role in guiding treatment strategies.