PURPOSE: A prolonged carcinostatic agent useful as a suture for operation, capable of releasing a toxic carcinostatic agent to a cancerous tissue securely and slowly, not accumulating a high polymer substance in the body, comprising an absorbable high polymer compound containing the carcinostatic agent.

CONSTITUTION: A prolonged carcinostatic agent in any type comprising an absorbable high polymer compound such as collagen, polyglycolic acid, polyvinyl alcohol, gelatin, etc. containing a carcinostatic agent such as 5-fluoro-2'-deoxyuridine, etc. The carcinostatic agent is used as a suture after operation of cancer extraction as a filament, or it in the form of a toothbrush is inserted into a solid cancer. Consequently, the carcinostatic agent can be securely medicated to the cancerous tissue, and the release concentration and rate of the carcinostatic agent can be controlled by the high polymer compound. The high polymer compound is absorbed in the body after the release of the carcinostatic agent, and does not remain for a long time.