Diagnostic performance of breast-specific gamma imaging in the assessment of residual tumor after neoadjuvant chemotherapy in breast cancer patients

To evaluate the diagnostic performance of breast-specific gamma imaging (BSGI) in the assessment of residual tumor after neoadjuvant chemotherapy (NAC) in breast cancer patients, female breast cancer patients who underwent NAC, preoperative ^99mTc-sestamibi BSGI, and subsequent definitive breast surgery were enrolled retrospectively. The accuracy of BSGI in the assessment of residual tumor presence and residual tumor size was evaluated and compared to that of magnetic resonance imaging (MRI) using pathology results as the gold standard. The sensitivity and specificity of BSGI for residual tumor detection in 122 enrolled patients were 74.0 and 72.2 %, respectively, and were comparable to those of MRI (81.7 and 72.2 %; P > 0.100). The residual tumor size was significantly underestimated by BSGI in the luminal subtype (P = 0.008) and by MRI in the luminal (P < 0.001) and HER2 subtypes (P = 0.032), with a significantly lesser degree of underestimation by BSGI than MRI in both subtypes. In the triple-negative subtype, both BSGI and MRI generated accurate tumor size measurements. The residual cellularity of triple-negative tumors was significantly higher than that of the non-triple-negative tumors (P = 0.017). The diagnostic performance of BSGI in the assessment of residual tumor is comparable to that of MRI in breast cancer patients. The assessment of residual tumor extent by BSGI depends on the molecular subtype, but BSGI may be more accurate than MRI. Underestimation of tumor size in the luminal and/or HER2 subtypes by BSGI and MRI may be due to low-residual cellularity.