Breast MRI for Evaluating Residual Tumor Size Following Neoadjuvant Chemotherapy: Clinicopathologic Factors and MRI Imaging Features Affecting Its Accuracy

Objectives: To investigate the accuracy of breast magnetic resonance imaging (MRI) for evaluating residual tumor size following neoadjuvant chemotherapy (NAC) and to identify clinicopathologic and MRI features affecting its accuracy. Materials and methods: We retrospectively assessed 109 women who underwent preoperative dynamic contrast-enhanced (DCE) MRI following NAC and subsequent surgery between April 2016 and August 2020. Preoperative MRI features, including Breast Imaging Reporting and Data System lexicon characteristics, size of residual enhancing lesion, tumor shrinkage pattern, and clinicopathologic features were investigated, and MRI and pathology findings were compared. Results: Residual tumor size on MRI showed high agreement with residual invasive tumor size on pathologic examination (ICC, 0.808, p<0.001). The residual tumor size measured by MRI and final pathologic size were concordant in 63/109 cases (57.8%), while MRI overestimated the size in 35/109 cases (32.1%). For estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative tumors, MRI tended to underestimate the residual tumor size compared with HER2-positive cancers (p=0.002) and triple-negative cancers (p=0.12). On MRI, tumors with concentric shrinkage patterns after NAC showed less size discrepancy with final pathologic tumor size than those with nonconcentric patterns (p=0.026). Conclusion: ER-positive/HER2-negative cancers are tended to underestimate the residual tumor size by MRI compared with other subtypes. Tumors with concentric shrinkage patterns after NAC showed less MRI/pathology size discrepancy.

Nomogram for predicting breast-conservation surgery after neoadjuvant chemotherapy.

1128 Background: The indications for neoadjuvant systemic treatment (NST) have broadened to early breast cancer patients and more patients can undergo breast conservation with results in better cosmetic outcomes. However, a significant number of patients with operable breast cancer still require mastectomy after NST with a small number of patients experiencing disease progression which may hinder complete surgical resection. Therefore, accurate prediction of each patient’s likelihood of achieving breast conservation after NST is important for establishing a treatment plan for patients with operable breast cancers. Methods: We identified 534 women from the Seoul National University Hospital Breast Care Center, who were stage II and III, and treated with neoadjuvant chemotherapy and surgery from Jan. 2001 to Dec. 2010. Breast conservation surgery (BCS) and tumor size reduction to less than 3cm were clinical outcome variables for nomograms, and we analyzed the various clinicopathologic factors best predicting these outcomes. To develop well-calibrated and exportable nomograms for BCS and for residual tumor size, we built each model in a training cohort and validated it in an independent validation cohort. Results: Of the 513 patients, pCR was observed in 10.5% and BCS was performed in 50.1%. The nomogram for predicting BCS and tumor size reduction to less than 3cm were constructed using logistic regressing model. Initial tumor size(p<0.001), the distance between the lesion and the nipple (p < 0.001), the presence of suspicious calcifications in the mammography (p = 0.0127) and multicentricity (p = 0.0146) were independently associated with breast conservation surgery. ER status (p = 0.001), initial tumor size (p < 0.001), histologic type (p = 0.012) were independently associated with a residual tumor size <3cm. Mastectomy rate in the larger than 3cm tumors were 72.7%, and breast conservation surgery in smaller than 3cm tumors were 63.2%. (p < 0.001). Conclusions: In conclusion, we have established a new model to predict BCS and residual tumor size after NST. The model showed the outperformed prediction accuracy compared with previous similar models with reflecting novel factors impacting on surgical decision making.