To analyze the influencing factors of the efficacy of neoadjuvant chemotherapy （NAC） in young patients with HER-2 low-expression breast cancer.

According to the inclusion and exclusion criteria，this retrospective study collected the clinical data of 68 young breast cancer patients with HER-2 low-expression （<40 years old） who received preoperative NAC in the Department of Oncology Surgery，Department of Breast Surgery of the First Hospital of Lanzhou University and Department of Breast Surgery of Gansu Provincial Cancer Hospital from December 2017 to July 2022. The pathological efficacy of NAC was evaluated by the Miller-Payne grading system. According to the grading results，the patients were divided into the poor pathological response group （grade 1-3，n=33） and the good pathological response group （grade 4-5，n=35）. The clinicopathological characteristics and hematological indexes were compared between two groups by chi-square test/Fisher's exact test and Mann-Whitney U test. Factors with statistically significant differences were included in multivariate logistic regression analysis to screen out the independent predictors of NAC efficacy in young patients with HER-2 low-expression，and accordingly a nomogram model was constructed and evaluated.

Among young breast cancer patients with HER-2 low-expression，there was no statistically significant difference in clinicopathological characteristics between two groups （all P<0.050）. Compared with the poor response group，the good response group had higher absolute lymphocyte count after NAC （post-Lym），platelet count after NAC （post-Plt），albumin after NAC （post-Alb），random venous plasma glucose before and after NAC （pre-RVPG，post-RVPG），and change value （ΔRVPG） （χ²=5.858，4.788，4.637，7.428，4.839，5.316； P=0.016，0.029，0.031，0.006，0.028，0.021）. Multivariate analysis showed that post-Alb （OR=7.713，95%CI： 1.620-36.716，P=0.010），post-RVPG （OR=14.612，95%CI： 2.225-95.939，P=0.005） and ΔRVPG （OR=9.639，95%CI： 2.511-36.997，P<0.001） were independent predictors of NAC efficacy in young breast cancer patients with HER-2 low-expression. Based on the results of multivariate logistic regression analysis，the nomogram model for predicting NAC efficacy in young patients with HER-2 low-expression was constructed. The area under the receiver operating characteristic curve was 0.797 （95%CI： 0.693-0.900）. The mean absolute error of the calibration curve was 0.042 （<0.050），indicating that the model had good calibration.

The efficacy of NAC in young breast cancer patients with HER-2 low-expression may be closely related to metabolism-nutrition status. Albumin，random venous plasma glucose and blood glucose fluctuation before and after NAC may become predictors of efficacy in this population，providing a basis for precise treatment.