Purpose: To evaluate the accuracy of the apparent diffusion coefficient (ADC) provided by diffusion-weighted imaging (DWI) in predicting the response to neoadjuvant chemotherapy (NACT) at baseline in patients according to their breast tumour phenotypes.
Materials & methods: This retrospective study was approved by our institutional review board. One hundred eighteen consecutive women with locally advanced breast cancer who had undergone NACT followed by breast surgery were included. DWI was performed at 1.5 T less than 2 weeks before NACT. We studied the correlation between pretreatment ADC and response in pathology after surgery according to immunohistochemical features and intrinsic subtypes (luminal A, luminal B, HER2-enriched, and triple-negative tumours).
Results: After surgery, the pathologist recognized 24 complete responders (CRps) and 94 non-complete responders (NCRps). No difference was identified between the pretreatment ADCs of the CRp and NCRp patients. There were differences in pretreatment ADCs among the luminal A (1.001 ± 0.143 × 10(-3) mm(2)/s), luminal B (0.983 ± 0.150 × 10(-3) mm(2)/s), HER2-enriched (1.132 ± 0.216 × 10(-3) mm(2)/s), and triple-negative (1.168 ± 0.245 × 10(-3) mm(2)/s; P = 0.0003) tumour subtypes. In triple-negative tumours, the pretreatment ADC was higher in NCRp (1.060 ± 0.143 × 10(-3) mm(2)/s) than in CRp patients (1.227 ± 0.271 × 10(-3) mm(2)/s; P = 0.047).
Conclusion: Pretreatment ADC can predict the response of breast cancer to NACT if tumour subtypes are considered. Key Points • Apparent diffusion coefficient helps clinicians to assess patients with breast cancer. • Pretreatment ADC is related to tumour grade and hormone receptor status. • Pretreatment ADC is lower in luminal A and B than in triple-negative tumours. • Pretreatment ADC is higher in complete than in non-complete responders to neoadjuvant chemotherapy.