: The therapeutic effect found histologically after surgery following neoadjuvant chemotherapy NAC correlates with patient prognosis. Such correlations must consider the remaining invasive lesions as well as intra-ductal components and lymph node metastasis. To this end, we compared the residual cancer burden RCB index with the conventional method of judging the histopathological therapeutic effect. We also took into account the clinicopathological features of patients related to recurrence and prognosis by the RCB index. We studied 244 cases of primary breast cancer in 238 patients who had undergone surgery after NAC in Showa University Hospital from 2005 to 2014. We classi ed the cases into groups based on the Japanese Breast Cancer Society s criteria for evaluating the histological therapeutic effect and the RCB index. The cases were also analyzed in regard to various clinicopathological factors. The prognosis was evaluated by drawing recurrence-free survival curves using the Kaplan-Meier method, and the log rank test was used to test statistical significance. The RCB index was evaluated for cases of Grade 0-1b that had a certain degree of residual tumor tissue. Comparison of the recurrence-free survival rates in each of the RCB index groups indicated a signi cant correlation, although only for patients with some degree of residual malignancy even after chemotherapy. We conclude that the RCB index can be used for providing a more precise prediction of recurrence.

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