PURPOSE:It is well known that tumor cells secrete endogenous tumor necrosis factor (en‐TNF) as a cytokine when stimulated with lipopolysaccharide (LPS). We, therefore, analyzed the biologic role of en‐TNF secreted by tumor cells themselves to learn the prognosis of patients and the susceptibility of tumors to biologic response modifiers in particular.METHODS:Patients with Dukes C colorectal tumors were studied after curative operation to determine the inducibility of en‐TNF by their primary cultured cells in response to LPS.RESULTS:Irrespective of the known clinicopathologic factors of the tumors, en‐TNF was produced in 21 of a total of 44 patients. The group of patients with clear en‐TNF production showed a significantly lower incidence of recurrence and/or metastasis and a higher survival rate than the group without en‐TNF production, suggesting a strong correlation between patient prognosis and inducibility of en‐TNF.CONCLUSION:Inducibility of en‐TNF by tumor cells themselves can be a novel prognostic factor for patients with colorectal tumor, especially of Dukes Stage C.