Factors associated with radiologic-pathologic discordance in magnetic resonance imaging after neoadjuvant chemotherapy for breast cancer

Background: Although breast MRI is known to be the best imaging modality for assessing the response after neoadjuvant chemotherapy (NAC), discordance still remains between MRI findings and final pathology findings. Purpose: To evaluate imaging and clinicopathologic factors associated with radiologic-pathologic discordance in breast cancer patients after NAC. Material and methods: This retrospective study included 104 breast cancer patients (mean age: 50.2 years) who underwent breast MRI examinations before and after NAC between June 2015 and December 2019. Radiologic complete response (rCR) was defined as equal or lesser enhancement compared with breast tissue in post-NAC MRI. Pathologic CR (pCR) was defined as absence of invasive cancer in final pathology. Imaging and clinicopathologic factors associated with radiologic-pathologic discordance were analyzed with logistic regression analysis. Results: Overall rCR and pCR rates were 37.5% (39/107) and 40.2% (43/107), respectively. Multivariate analysis revealed that the presence of non-mass enhancement (odds ratio [OR], 3.6; 95% confidence interval [CI], 1.1–11.2; P = 0.03) and multicentric lesions on pre-NAC MRI (OR, 4.2; 95% CI, 1.2–14.9; P = 0.03) were independently associated with radiologic-pathologic discordance. False-positive rate for predicting residual tumor was the most prevalent in HER2-positive cancers (86.7%). Conclusion: When determining rCR, the presence of non-mass enhancement and multicentric lesions on pre-NAC MRI, and HER2-positive cancers should be interpreted with caution.