Background: Neoadjuvant endocrine therapy (NET) can help downstage certain breast cancers prior to surgical resection. This study measured the accuracy of conventional mammography (MMG), ultrasound (US), magnetic resonance imaging (MRI), and contrast-enhanced mammography (CEM) for assessing breast tumor size in response to NET. Patients and Methods: Patients who underwent surgery after NET from 2013 to 2021 were identified. The maximal dimension of residual tumor on imaging was compared with the maximal dimension on final pathology. Lin’s concordance correlation coefficient (rc) and Spearman’s rank correlation coefficient (r) were used to assess agreement. Results: In total, 119 patients with invasive breast cancer underwent NET, posttreatment imaging, and surgery. Tumor size reported on posttreatment CEM correlated with size on final pathology to within 1 cm in n = 42 (58%) of patients, equivalent to the accuracy of MRI (n = 35, 58%). Size was accurately predicted by US in 54% and in 48% of MMG. Posttreatment imaging tumor size was moderately correlated with final tumor size on pathology CEM (r = 0.49; rc = 0.38), MRI (r = 0.52; rc = 0.45), and US (r = 0.41; rc = 0.28). MMG was weakly correlated (r = 0.21; rc = 0.16). Similar findings were shown in subgroup analysis; in those who received all four post-NET imaging, CEM and MRI again performed comparably, with r = 0.36 and 0.41, respectively, US (r = 0.43) and MMG (r = 0.28). Conclusions: Compared with mammography and US, CEM and MRI had higher accuracy in estimating final tumor size for breast cancers treated with NET. Contrast-enhanced imaging is a helpful adjunct when response to preoperative therapy will impact clinical management.
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