Preliminary experiences of PET/MRI in predicting complete response in patients with breast cancer treated with neoadjuvant chemotherapy

Clinical response predictions through image examinations after neoadjuvant chemotherapy (NAC) for breast cancer is important. The present study aimed to evaluate the utility of a novel imaging modality, positron-emission tomography/magnetic resonance imaging (PET/MRI), in predicting the pathological complete response (pCR) to NAC in patients with early breast cancer. A total of 74 patients underwent PET/MRI, mammography (MG), including tomosynthesis, and ultrasound (US) after NAC. The complete response was predicted using each modality and these outcomes were compared accordingly. In terms of PET/MRI, complete response (CR) was defined as the disappearance of 18F-fluorodeoxyglucose uptake and the absence of enhanced lesions with contrast enhanced MRI. In MG and US, undetectable lesions were considered as CR. The background and tumor characteristics of patients were also analyzed between the pCR and non-pCR cases. Overall, 18 (24.3%) of the 74 patients achieved pCR. The overall sensitivity and specificity of PET/MRI were 72.2 and 78.6%, respectively. Both the sensitivity in hormone receptor (HR)-positive cases and the specificity in HR-negative cases were 100%. HR-negative and human epidermal growth factor receptor 2 (HER2)-positive cases demonstrated a significant association with pCR compared with HR-positive cases and triple negative cases (P=0.017). Furthermore, patients with ‘mass’ type lesions evaluated by MRI before NAC experienced pCR with a higher frequency than those with ‘non-mass’ type lesions. There was a statistically significant difference between the two groups (P=0.018). In conclusion, PET/MRI is a different diagnostic approach that utilizes a multi-modality system. It demonstrates reasonable diagnostic accuracies of the responses of NAC with reference to hormonal subtypes in breast cancer.