Advanced gastric cancer is a systemic disease that requires adjuvant therapy targeted at eliminating disseminated tumor cells (DTCs). We investigated whether the apoptosis-inducing human monoclonal IgM antibody SC-1 was able to reduce the number of disseminated gastric cancer cells in blood and bone marrow. Human gastric tumor specimens with positive expression of the SC-1 receptor were transplanted in nude mice with metastasizing gastric cancer. After tumor growth (4-6 weeks) animals were randomly allocated to intraperitoneal 100 microg SC-1 (n=23) or 100 microg human IgM (n=23). One week later, animals were sacrificed and blood and bone marrow specimens were obtained. A nested RT-PCR for cytokeratin 20 (CK-20) from blood and bone marrow of mice was performed for detection of disseminated tumor cells. Animals receiving SC-1 had significantly fewer DTCs than did control animals (p=0.0011). None of the SC-1 mice had DTCs simultaneously in both blood and bone marrow versus four of the control animals (p=0.0363). The reduction of DTCs in SC-1 animals was due to reduction in bone marrow (p=0.032 compared to controls), but not in blood (p=0.1158). Treatment with SC-1 significantly reduced the number of DTCs in bone marrow in this animal model.