Effects of hypovolemia and transfusion on tumor growth in MCA-tumor-bearing rats. Pretransplant blood transfusion has been shown to significantly affect the outcome of renal transplantation. Evidence regarding the association of blood transfusions with growth or recurrence of solid tumors is still conflicting both in clinical and in experimental studies, although diminished survival has been suggested in several studies. To determine the influence of blood transfusions and hypovolemia, as separate or combined factors, on tumor growth, we evaluated the weight of a subcutaneously implanted sarcoma (methylcholanthrene-induced) in 35 rats. After reaching 1% tumor burden (day 0), the animals were separated into two groups: hypovolemia (shed volume, 15 ml/kg) or normovolemia. These groups were further divided according to resuscitation: OO (no resuscitation), BL (receiving syngeneic blood stored in citrate phosphate dextrose for 4 days, 15 ml/kg), SL (receiving 0.9% sodium chloride, 45 ml/kg). Tumor dimensions were determined daily by external measurement, and tumor weight was calculated. Hypovolemia exerted a significant influence on tumor growth, independent of the resuscitation modality. The rats that received blood transfusions showed an increased rate of tumor growth, compared to the animals that received saline solution or no treatment. No interaction was noted between the effects produced by hypovolemia and blood transfusion. We conclude that the hypovolemic event enhanced tumor growth independently of the resuscitation, and transfusion of citrate phosphate dextrose-blood stored for 4 days did influence tumor growth in this model. We suggest that the effect of blood transfusion in patients with cancer has to be redefined to account for the influence of possible hypovolemic events. 