Thiotepa or Thio-TEPA (NSC-6396; AI3 24916; WR45312; Girostan), an approved drug for cancer treatment, is a potent DNA alkylating agent with antitumor activity. Thiotepa is a polyfunctional, organophosphorus alkylating agent and a stable derivative of N,N',N''-triethylenephosphoramide (TEPA), with antineoplastic activity. Upon administration, thiotepa is converted into highly reactive ethylenimine groups, which covalently bind to nucleophilic groups in DNA and demonstrate a preference for the N7 position of guanine bases. This induces crosslinking of alkylated guanine bases in double-stranded DNA, interferes with both DNA replication and cell division, and results in both the induction of apoptosis and the inhibition of cell growth.