To the Editor:
It is postulated that blood transfusion has been associated with cancer promotion because of the adverse effect of blood transfusion on the immune system. In contrast to a number of cited studies, Weightman et al. found no association between transfusion of up to six units of blood and long-term survival in cardiac surgery patients.1They attributed this discrepancy, at least in part, to their multivariate analysis that included anemia as a risk factor.
Because cardiopulmonary bypass (CPB) causes a state of temporary immunodeficiency, it has been suggested that CPB negatively affects the host defense against malignancy. Platell2found that the cancer-specific survival rates of patients with colon cancer were reduced after surgery with CPB. Thus, as an alternative explanation for their discrepancy, I hypothesize two related possibilities that will need to be tested. Perhaps, the incremental adverse effect of blood transfusion on the immune system in patients who have been on CPB is not enough to make a measurable effect on tumor promotion and long-term outcome until a sufficiently large number of packed erythrocytes have been transfused. Second, if CPB and blood transfusion affect the immune system in a similar manner, there may be no incremental adverse effect on the immune system until a sufficiently large number of packed erythrocytes have been transfused. Consistent with the notion that an adverse effect on the immune system causes reduced long-term survival (although at odds with other studies that have compared long-term results of off-pump vs. CPB cardiac surgery), Weightman et al. reported a reduced hazards ratio of 0.63 for patients who were underwent off-pump surgery where, presumably, there is less immunosupression, although this finding (possibly because of a small sample size) was not statistically significant.
Albert Einstein Medical Center, Thomas Jefferson School of Medicine, Philadelphia, Pennsylvania. rothj@einstein.edu
