Retrospective observational study of Kampo medicines for suppressing the side effects of endocrine therapy in the treatment of breast cancer: a pilot study

Background Long-term endocrine therapy for breast cancer often causes menopause-like symptoms, affecting quality of life. Although Japanese traditional (Kampo) medicine is utilized for relief, research remains limited. Objective This retrospective observational study aimed to evaluate the efficacy of Kampo medicines in managing endocrine therapy-related side effects in breast cancer patients. Methods Data from breast cancer patients receiving endocrine therapy treated with Kampo medicines at Japanese Red Cross Ishinomaki Hospital between July 2017 to June 2024 were analyzed. Symptom severity was measured using a Numerical Rating Scale (NRS; 0–10). Kampo medicine, administered by a specialist, was tailored to individual symptoms and physical findings. Multivariate analysis was performed to examine the association between symptom relief. Symptom progression was analyzed using Kaplan-Meier curves, and outcomes were compared using the log-rank test. Results Fifty-three patients (median age: 54) were enrolled. Vasomotor, motor/sensory, and psychiatric symptoms accounted for 90% of complaints. After 6 months, 75% of patients reported NRS scores of 3 or less (enabling them to perform daily activities without difficulty). Keishibukuryogan (KBG) or keishibukuryogankayokuinin (KBGY) were the most prescribed (41.5%). Multivariate analysis indicated KBG/KBGY was significantly associated with symptom relief (Hazard Ratio 4.18; 95% CI 1.03–16.92; p = 0.046). Patients prescribed KBG/KBGY experienced significantly faster overall symptom improvement than those on other Kampo medicines ( p = 0.022). Conclusion Kampo medicines are effective in alleviating side effects in breast cancer patients undergoing endocrine therapy. KBG/KBGY has shown promise in reducing overall symptoms.