NAC is used to test response or resistance of chemotherapeutic agent and reduce micrometastatic diseases [16, 17]. Evaluating tumor response after NAC is important for determining future treatment plans and predicting long-term outcomes. Currently, CEMRI is the imaging modality for response monitoring . CEMRI yields superior outcomes compared to mammography and US for identifying residual disease following NAC [19, 20]. However, CEMRI has several limitations, such as long exam time, high cost, low accessibility, and longer interpretation time. In comparison, CEDM is known for shorter procedure time, cheaper price, easy interpretability, shorter interpretation time, and no claustrophobia risk [10, 21, 22]. Also, female patients do need to schedule their imagining appointment according to menstrual cycle. Some clinicians have suggested to conduct CEDM and CEMRI according to menstrual phase; however, some argue no clear pattern in background parenchymal enhancement variation across the menstrual cycle for either CEDM or CEMRI . CEDM also revealed equivalent result for detecting primary and multifocal cancers and estimating extent of cancers compared to CEMRI .
In present study, CEDM was evaluated for detecting and measuring remnant tumors after NAC. Although CEDM underestimated remnant tumor size in some patients, the difference between CEDM and pathologic results was less than 1 cm in 63.3% of cases. Barra et al.  reported similar results, with a difference between CEDM and pathologic size within 1 cm in almost 70% of cases. Limits of agreement with the residual tumor were lower for CEMRI than for CEDM, which was consistent with that found by Patel and colleagues .
Regarding diagnostic performance, CEDM demonstrated better specificity, PPV, and NPV compared to CEMRI, though CEMRI had better sensitivity than CEDM. Similarly, other studies reported comparable specificity and PPV for CEDM [6, 25]. All women with radiologic CR on CEMRI had negative CEDM results. Our results also showed good correlation and concordance of CEDM with histopathologic result after NAC (Figs. 2 and 3, Table 3).
CEDM and CEMRI both underestimated the extent of remnant cancers (mean tumor sizes from CEDM, CEMRI, and pathology were 1.22 cm, 1.13 cm, and 1.89 cm, respectively). Iotti et al.  also reported underestimation of tumor size by CEDM and CEMRI after NAC. Wu et al.  explained this discrepancy as an antiangiogenic effect of chemotherapeutic agents used in CEDM and CEMRI, such as taxanes and anthracyclines. This anti-vascular effect, which lacks a surrounding inflammatory response, lowers enhancement of tumor tissue and, thus, can result in tumor underestimation .
Limitations of the present study are associated several factors. First, we enrolled a small number of patients. This was possibly because patients lacked an understanding of CEDM. Since CEDM was recently introduced in South Korea, patients were not familiar with it, and most refused to undergo additional mammography because of the pain induced by breast compression during the procedure. Second, the ability to detect residual ductal carcinoma in situ (DCIS) or suspicious microcalcifications remains unknown for both CEDM and CEMRI. CEDM and CEMRI identify occult breast cancer using mechanism of tumor angiogenesis ; however, the underlying mechanism of tumor angiogenesis depends on subtype of breast cancer. Neo-angiogenesis is more prominent in IDC and is not always exist in DCIS and lobular carcinomas . In our study, none of pCR patients showed residual DCIS component on residual tumor. The feasibility of CEDM for DCIS should be further evaluated. Third, we could not differentiate the diagnostic accuracy of CEDM according to presence or absence of microcalcifications. Finally, we could not assess the accuracy of CEDM according to molecular subtype, and further investigations are needed.
Our study also has several strengths. First, this is the first CEDM study conducted among breast cancer patients who received NAC in South Korea.. Second, we found that CEDM is secure and practical. There was no technical failures during procedure and one patient had side effects during CEDM examinations. The patient vomiting one minutes following injection of contrast media. The symptoms disappeared soon. Finally, because this was a prospective study, there was no inherent bias.