A methylated derivative of carmustine with antineoplastic activity. As an alkylating agent, semustine forms covalent linkages with nucleophilic centers in DNA, causing depurination, base-pair miscoding, strand scission, and DNA-DNA cross-linking, which may result in cytotoxicity. or A substance that has been studied in the treatment of some types of cancer. Semustine damages the cell’s DNA and may kill cancer cells. It is a type of alkylating agent and a type of nitrosourea.