ObjectiveTo explore the effect of trastuzumab combined with TP regimen in the treatment of breast cancer, and to analyze its effect on plasminogen activator inhibitor (PAI)-1, human epidermal growth factor receptor (HER) 2 receptor and lymphocyte subsets.MethodsA total of 100 breast cancer patients in Yingshang County People's Hospital from January 2020 to November 2024 were selected for the study and randomly divided into the observation group and the control group, with 50 cases in each group. Five cases dropped out during the study. Eventually, the patients were divided into an observation group of 48 cases and a control group of 47 cases. The control group was treated with the TP regimen, while the observation group was treated with trastuzumab combined with TP regimen. The clinical efficacy, PAI-1, HER2, lymphocyte subsets, tumor markers and the occurrence of adverse reactions of the two groups were compared.ResultsAfter treatment, the total effective rate of the observation group was higher than that of the control group (79.17% vs. 53.19%, P<0.05). The level of PAI-1 and the expression of HER2 receptor in the observation group were lower than those in the control group (P<0.05). The levels of cluster of differentiation(CD) 3⁺ and CD4⁺ in the observation group were higher than those in the control group (P<0.05), while CD8⁺ was lower than that in the control group (P<0.05). The levels of carbohydrate antigen 153, tissue polypeptide specific antigen and carcinoembryonic antigen in the observation group were lower than those in the control group (P<0.05). There was no statistically significant difference in adverse reactions between the two groups (P>0.05).ConclusionTrastuzumab combined with TP regimen has a significant therapeutic effect in the treatment of breast cancer. It can effectively inhibit tumor progression and also improve the levels of PAI-1, HER2 and the distribution of peripheral blood lymphocyte subsets.