• Low dose total body irradiation added to allo-HCT conditioning does not further increase the risk of subsequent malignancy

  • A greater number of pre-transplant chemotherapy cycles are associated with an increased risk of subsequent malignancy after allo-HCT.

Subsequent malignancies (SM) present a significant burden of morbidity and are a common cause of late mortality in survivors of allogeneic HCT (hematopoietic cell transplant). Previous studies have described total body irradiation (TBI) as a risk factor for the development of SM in allo-HCT survivors. However, most studies of the association between TBI and SM have examined high dose TBI regimes (typically ≥600cGy) and thus little is known about the association between low dose TBI regimens and risk of SM. Thus, we set out to compare the cumulative incidence of SM in Albertan patients who received busulfan/fludarabine alone versus busulfan/fludarabine plus 400 cGy TBI. Of 674 included patients, 49 patients developed a total of 56 malignancies at a median of 5.9 years post-transplant. The cumulative incidence of SM at 15 years post-HCT in the entire cohort was 11.5% (95% CI 8.5-15.6%): 13.4% (95% CI 9.1-19.3%) in the no-TBI group and 10.8% (95% CI 6.6-17.4%) in the TBI group. In the multivariable model, TBI was not associated with SM, while number of pre-HCT cycles of chemotherapy was. The standardized incidence ratio for the entire cohort, as compared to the age, sex and calendar-year matched general population was 1.74. Allo-HCT conditioning that includes low dose TBI does not appear to increase risk of SM as compared to chemotherapy-alone conditioning.

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