Diffusion-weighted imaging in assessing pathological response of tumor in breast cancer subtype to neoadjuvant chemotherapy.

Objective: To investigate the efficacy of diffusion-weighted imaging (DWI) for reflecting and predicting pathological tumor response in breast cancer subtype to neoadjuvant chemotherapy (NAC).

Methods: The retrospective study included 176 patients with breast cancer who underwent magnetic resonance imaging (MRI) examinations before and after NAC prior to surgery. The pre- and post-NAC apparent diffusion coefficient (ADC) values of tumor were measured respectively on DWI. The pathological response was classified into either a complete response (pCR) or as a noncomplete response (pNCR) to NAC with the Miller & Payne system. The relationship between the ADC value and the pathological response was assessed according to intrinsic subtypes (Luminal A, Luminal B, HER2-enriched, and triple negative) defined by immunohistochemical features.

Results: Multiple comparisons respectively showed that pre-NAC and post-NAC ADC were significantly different among four subtypes (P < 0.001). After the comparison between two different subtypes, the pre-NAC ADC value of the triple-negative and HER2-enriched subtypes were significantly higher than Luminal A (P < 0.001 and P < 0.001) and Luminal B subtype (P < 0.001 and P = 0.009), and the post-NAC ADC of triple-negative subtype was significantly higher than the others (P < 0.001). The pre-NAC ADC of pCRs was significantly lower than that of pNCRs only in the triple-negative subtype among four subtypes (P < 0.001), and the post-NAC ADC of pCRs was significantly higher than that of pNCRs in each subtype (P < 0.001).

Conclusions: DWI appears to be a promising tool to determine the association of pathological response to NAC in breast cancer subtypes.