Background In cancer patients, allogeneic blood transfusion is associated with poorer prognosis, but the independent effect of the transfusion is controversial. Moreover, mediating mechanisms underlying the alleged cancer promoting effects of blood transfusion are unknown, including the involvement of donors’ leukocytes, erythrocytes, and soluble factors. Method Two syngeneic tumor models were used in Fischer 344 rats, the MADB106 mammary adenocarcinoma and the CRNK-16 leukemia. Outcomes included host ability to clear circulating cancer cells, and host survival rates. The independent impact of blood transfusion was assessed, and potential deleterious characteristics of the transfusion were studied, including blood storage duration, the role of erythrocytes, leukocyte, and soluble factors, and the kinetics of the effects. Results Blood transfusion was found to be an independent and significant risk factor for cancer progression in both models, causing up to four-folds increase in lung tumor retention, and doubling mortality rates. Blood storage time was the critical determinant of these deleterious effects, regardless of whether the transfused blood was allogeneic or autogenic. Surprisingly, aged erythrocytes (9 days and older), rather than leukocytes or soluble factors, mediated the effects, which occurred in both operated and non-operated animals. The effects of erythrocytes transfusion in the MADB106 model emerged immediately, and dissipated within 24 hours. Conclusions In rats, transfusion of fresh blood is less harmful than transfusion of stored blood in the context of progressing malignancies. Further studies should address mediating mechanisms through which erythrocytes’ storage-duration can impact the rate of complications while treating malignant diseases and potentially other pathologies.

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These findings suggest that the working conditions of anesthesiologists are associated with specific immune alterations, including a shift towards a Th2 cytokines' dominance, and an elevated pro-inflammatory cytokine response. A reduced Th1 profile has been related to increased susceptibility to infections, and high pro-inflammatory cytokine levels were recently proposed as etiological factors in cardiovascular diseases and in depression.