Can Routine Imaging After Neoadjuvant Chemotherapy in Breast Cancer Predict Pathologic Complete Response?

Background. This study evaluated breast imaging procedures for predicting pathologic complete response (pCR = ypT0) after neoadjuvant chemotherapy (NACT) for breast cancer to challenge surgery as a diagnostic procedure after NACT. Methods. This retrospective, exploratory, monocenter study included 150 invasive breast cancers treated by NACT. The patients received magnetic resonance imaging (MRI), mammography (MGR), and ultrasound (US). The results were classified in three response subgroups according to response evaluation criteria in solid tumors. To incorporate specific features of MRI and MGR, an additional category [clinical near complete response (near-cCR)] was defined. Residual cancer in imaging and pathology was defined as a positive result. Negative predictive values (NPVs), false-negative rates (FNRs), and false-positive rates (FPRs) of all imaging procedures were analyzed for the whole cohort and for triple-negative (TN), HER2-positive (HER2+), and HER2-negative/hormone-receptor-positive (HER2-/HR+) cancers, respectively. Results. In 46 cases (31 %), pCR (ypT0) was achieved. Clinical complete response (cCR) and near-cCR showed nearly the same NPVs and FNRs. The NPV was highest with 61 % for near-cCR in MRI and lowest with 44 % for near-cCR in MGR for the whole cohort. The FNRs ranged from 4 to 25 % according to different imaging methods. The MRI performance seemed to be superior, especially in TN cancers (NPV 94 %; FNR 5 %). The lowest FPR was 10 % in MRI, and the highest FPR was 44 % in US. Conclusion. Neither MRI nor MGR or US can diagnose a pCR (ypT0) with sufficient accuracy to replace pathologic diagnosis of the surgical excision specimen.