Tamoxifen-induced neutropenia and leukopenia in a breast cancer patient: a case report and literature review

Background: Tamoxifen is a cornerstone of endocrine therapy for hormone receptor-positive breast cancer. While its common side effects are well-documented, severe hematological toxicities such as neutropenia and leukopenia are extremely rare. Case presentation: We report a case of a 37-year-old premenopausal woman with hormone receptor-positive breast cancer who developed neutropenia and leukopenia three months after initiating adjuvant tamoxifen (20 mg/day). Despite transient improvements with supportive therapies (leucogen tablets and Compound Ejiao Jiang), cytopenias persisted. Tamoxifen was discontinued and switched to ovarian function suppression (leuprolide) plus an aromatase inhibitor (exemestane). Within four weeks, neutrophil and leukocyte counts normalized and remained stable over six months of follow-up. Conclusion: This case highlights the importance of recognizing tamoxifen-induced hematological toxicity. Regular blood count monitoring is essential, and in premenopausal women intolerant to tamoxifen, switching to ovarian function suppression plus an aromatase inhibitor is a safe and effective alternative.