Hemorrhagic cystitis as an unexpected adverse reaction to temozolomide: case report.

A case is reported in which temozolomide, a promising new DNA alkylating agent, was successfully used to treat radiation refractory metastatic brain tumors arising from primary breast cancer. However, the treatment had to be terminated after the second round of treatment due to the development of hemorrhagic cystitis. This side effect was totally unexpected. Another class of alkylating agents (cyclophosphamide and related compounds) exhibits this side effect caused by a prevalent acrolein metabolite. Temozolomide and its sister compounds, dacarbazine and 5-(3-methyltriazen-1-yl)imidazole-4-caroxamide, have never been reported to have this adverse reaction. This case serves to alert physicians to the existence of a possible subpopulation of patients who may experience hemorrhagic cystitis on treatment with imidazotetrazines by a mechanism that is yet to be established.