Severe hyponatremia and diabetes insipidus caused by low-dose cyclophosphamide in breast cancer patients: A case report and literature review.

Rationale: Cyclophosphamide (CTX) is widely used in the treatment of malignancies and autoimmune diseases. Although severe hyponatremia caused by low-dose CTX chemotherapy is uncommon, it can lead to serious complications and even death.

Patient Concerns: A 44-year-old woman with left-sided breast cancer suddenly experienced headaches, disorientation and weakness after receiving low-dose neoadjuvant chemotherapy combined with CTX and doxorubicin.