A new histological therapeutic classification system to predict eradicated and residual lymph nodes in breast cancer after neoadjuvant chemotherapy

The indication for neoadjuvant chemotherapy (NAC) has recently broadened to include its use in the treatment of initial stage breast cancer. Axillary lymph node metastasis after NAC in breast cancer is a poor prognostic factor. Thus, the prediction of lymph node metastasis is important to estimate the prognosis of breast cancer patients after NAC. Therefore, we focused on residual carcinoma patterns of primary breast tumors after NAC and examined the correlation between the patterns and lymph node metastasis. In this study, we examined 50 breast cancer specimens and associated dissected lymph nodes after NAC. We divided 40 cases into an eradicated lymph node group and a residual lymph node group to analyze residual carcinoma patterns of primary breast tumors. Residual carcinoma patterns were classified according to the cell density of carcinoma cells: dense, focal/nested and sporadic/in-situ. There were significant differences in residual carcinoma patterns (P<0.01) among the three pattern groups. There was a high incidence of dense patterns in the residual lymph node group and a high incidence of sporadic/in-situ patterns in the eradicated lymph node group. Analysis of residual carcinoma patterns of primary breast tumors and clinicopathological factors demonstrated that there were significant differences in tumor reduced ratio on CT (P<0.001), primary tumor area before NAC (P<0.01), primary tumor area after NAC (P<0.00001), intrinsic subtype (P<0.01), Ki-67 labeling index (P<0.01), histological grade (P<0.05) and mitotic count (P<0.01) between the dense and non-dense groups. Therefore, our results suggest that the residual carcinoma pattern is useful for predicting eradicated or residual lymph nodes and the malignant potential in breast cancer after NAC.