Low-dose cyclophosphamide associated with hemorrhagic cystitis in a breast cancer patient

Hemorrhagic cystitis is a known complication of high-dose cyclophosphamide treatment, generally occurring at doses greater than 100 g. There are few reports of hemorrhagic cystitis occurring with low-dose cyclophosphamide therapy, and this complication has not been described in breast cancer patients. We present a case of a patient with stage IIB breast cancer who developed clinical, radiographic, and pathologic evidence of hemorrhagic cystitis after a single 600 mg/m² dose of cyclophosphamide. Three subsequent cycles of cyclophosphamide with the addition of IV hydration and MESNA were given without complication, and the patient's urologic symptoms resolved. Repeat cystoscopy demonstrated pathologic resolution of the cystitis. We review the literature regarding proposed mechanisms of hemorrhagic cystitis, and discuss the applicability of these hypotheses in our patient.