Objective To investigate the symptom clusters and sentinel symptoms in breast cancer patients during chemotherapy intervals, and to provide a basis for the management of symptom clusters.Methods A general information questionnaire and the Breast Cancer Chemotherapy Symptom Assessment Scale were used to investigate 381 breast cancer patients undergoing chemotherapy.Principal component analysis was employed to extract symptom clusters, and the sentinel symptoms of the symptom clusters were determined based on the results of association analysis using the Apriori algorithm.Results Five main symptom clusters were identified:the gastrointestinal symptom cluster (5 symptoms), emotional symptom cluster (4 symptoms), somatic symptom cluster (5 symptoms), pain symptom cluster (2 symptoms), and body image symptom cluster (2 symptoms).Decreased appetite was the sentinel symptom of the gastrointestinal symptom cluster.Low mood was the sentinel symptom of the emotional symptom cluster.Decreased libido was the sentinel symptom of the somatic symptom cluster. Headache was the sentinel symptom of the pain symptom cluster.No sentinel symptom was identified for the body image symptom cluster.Conclusion Breast cancer patients during chemotherapy intervals experience symptom clusters with corresponding sentinel symptoms.Identifying these sentinel symptoms as nursing warning signals enables targeted nursing interventions to prevent or mitigate symptom cluster progression, thereby improving patients′ quality of life.