Impact of splenectomy and immunochemotherapy on survival following gastrectomy for carcinoma: covariate interaction with immunosuppressive acidic protein, a serum marker for the host immune system. Tumor Marker Committee for the Study Group of Immunochemotherapy with PSK for Gastric Cancer.

The role of the spleen in tumor immunology is still controversial in that it can either enhance or suppress the antitumor immune response depending on the tumor-bearing host. To clarify this biphasic effect of the spleen, a clinical evaluation of splenectomy in conjunction with immunotherapy and the host immune status was performed in gastric cancer patients. The effect of splenectomy and immunotherapy in 253 gastric cancer patients enrolled in a prospective randomized trial (SIP) was analyzed using the Cox's proportional hazards model in terms of the covariate interaction of the preoperative immunosuppressive acidic protein (IAP) level. In patients with high IAP levels (>580 microg/ml) with predicted negative antitumor immune reactions, splenectomy improved the prognosis. In patients with lower IAP values, conversely, the preservation of the spleen and immunotherapy demonstrated a significant benefit to survival. The spleen was shown to have a biphasic activity in terms of its antitumor immune response depending on the IAP level of the patient. The effect of immunotherapy is significantly influenced by the activity of spleen cells. The preoperative IAP level is therefore considered to be a possible indicator for the effectiveness of splenectomy and immunotherapy in curatively resected gastric cancer patients.