Liu, et al.: Antitumor Studies of Earthworm Fibrinolytic Enzyme Component A on MCF-7Earthworm fibrinolytic enzyme from Chinese earthworm Eisenia foetida was isolated to investigate its antitumor activity in breast cancer cells. The protein isolated was characterised as earthworm fibrinolytic enzyme using the fibrin plate method. The molecular weight of earthworm fibrinolytic enzyme component was determined to be 25 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis assay using a standard protein ladder. Earthworm fibrinolytic enzyme can markedly inhibit the growth and migration of MCF-7 cells in a dose and time-dependent manner. In addition, MCF-7 cells treated with earthworm fibrinolytic enzyme (40 μg/ml) began to undergo apoptosis after 24 h. Expression of focal adhesion kinase and CD44v6 measured using reverse transcription polymerase chain reaction and Western blot was down-regulated in a concentration-dependent manner (20-80 μg/ml), resulting in the suppression of MCF-7 cells adhesion. The obtained earthworm fibrinolytic enzyme displayed an antitumor effect on MCF-7 cells in vitro, revealing the therapeutic potential of E. foetida.