Objective To explore the predictive effect of systemic immune-inflammation index (SII) on pathological complete response (pCR) of breast cancer patients to neoadjuvant chemotherapy and its relation with p53.

Methods We retrospectively analyzed the clinicopathological data of 387 female breast cancer patients who received neoadjuvant chemotherapy and surgery. Logistic regression model was used for univariate and multivariate analyses.

Results In this study, 72 (18.6%) patients received neoadjuvant chemotherapy and obtained pCR, including 48 patients in the low SII group and 24 patients in the high SII group; 39 cases in the p53 negative group and 33 cases in the positive group. Univariate analysis showed that pCR was correlated with clinical T stage, hormone receptor status, HER2, Ki67 value, molecular subtype, p53 and SII (all P < 0.05). Multivariate analysis showed that clinical T stage, Ki67 value, molecular typing, p53 and SII were independent predictors of pCR in breast cancer patients. The pCR rate of the low SII group with negative p53 was the highest.

Conclusion Systemic immune inflammation index is an independent predictor of pathological complete response of breast cancer patients to neoadjuvant chemotherapy, with the characteristics of simplicity, convenience and high repeatability. The pCR rate of patients in the low SII group with negative p53 is high.