Decreased background parenchymal enhancement of the contralateral breast after two cycles of neoadjuvant chemotherapy is associated with tumor response in HER2-positive breast cancer

Background: Several recent studies have focused on the association between background parenchymal enhancement (BPE) and tumor response to neoadjuvant chemotherapy (NAC), but early prediction of tumor response based on BPE has yet not been investigated. Purpose: To retrospectively investigate whether changes in the BPE of the contralateral breast following NAC could help predict tumor response in early stage HER2-positive breast cancer. Material and Methods: Data from 71 patients who were diagnosed with unilateral HER2 positive breast cancer and then underwent NAC with trastuzumab before surgery were analyzed retrospectively. Two experienced radiologists independently categorized the patients' levels of BPE of the contralateral breast into four categories (1 = minimal, 2 = mild, 3 = moderate, 4 = marked) at baseline and after the second cycle of NAC. After undergoing surgery, 34 patients achieved pathologic complete response (pCR) and 37 patients had residual disease (non-pCR). The association between BPE and histopathologic tumor response was analyzed. Result: The level of BPE was higher in premenopausal than post-menopausal women both at baseline and after the second cycle of NAC (P < 0.005). A significant reduction in BPE (P < 0.001) was observed after the second NAC cycle; however, a more obvious decrease in BPE was identified in premenopausal relative to post-menopausal women P = 0.041). No significant association was identified between pCR and baseline BPE (P = 0.287). However, after the second NAC cycle, decreased BPE was significantly associated with pCR (P = 0.003). Conclusion: For HER2-positive patients, changes in BPE may serve as an additional imaging biomarker of treatment response at an early stage.