Unexpected thrombocytopenia of a rare tamoxifen-induced complication in breast cancer therapy: A case report.

BACKGROUND: Tamoxifen, a selective estrogen receptor modulator, is pivotal in managing hormone receptor-positive breast cancer. While its common side effects are well-documented, tamoxifen-induced thrombocytopenia is a rare, serious adverse event requiring drug discontinuation. CASE SUMMARY: We report a case of tamoxifen-induced thrombocytopenia in a 51-year-old premenopausal woman with breast cancer, occurring within 4 weeks of initiating adjuvant tamoxifen therapy. Platelet counts normalized after drug cessation, but thrombocytopenia recurred upon rechallenge, leading to permanent discontinuation. CONCLUSION: This case underscores the need for regular complete blood count monitoring in patients on tamoxifen to detect rare hematologic adverse events promptly.