Thiotepa is an antineoplastic agent of the alkylating agent class. Belonging to the nitrogen mustard family, it is highly toxic, and "according to the Fourth Annual Report on Carcinogens (NTP 85-002, 1985), thiotepa may reasonably be anticipated to be a carcinogen. It causes skin, gastrointestinal, CNS, and bone marrow damage. "
It disrupts DNA replication and transcription of RNA, with an overall suppression of nucleic acid activity. Thiotepa also possesses some immunosuppressive activity. While it is no longer a first-line agent for any cancer, it has a role in the management of effusions from metastatic tumors. Sclerosing agents are often used for treating effusions, thiotepa may be preferred due to its direct effects against neoplasms.