Background: Total body irradiation (TBI)-based allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment for selected patients with acute myeloid leukemia (AML). Yet, secondary malignancies contribute to long-term morbidity and mortality with TBI potentially influencing these risks.
Methods: This retrospective study analyzed the cumulative incidences of secondary solid malignancies and precancerous lesions of 89 consecutive AML patients after TBI-based conditioning before 1st allo-HSCT between 2000 and 2016. TBI was performed with an average dose rate of 4 cGy/min and a twice-daily fractionation. Cause-specific hazard models analyzed risk factors for secondary malignancies/precancerous lesions and the competing risks of dying before developing secondary malignancies/precancerous lesions.
Results: The median patient age at TBI was 42.5 years (interquartile range, 32.5-51.2), while the median follow-up was 15.2 years (interquartile range, 13.0-18.2). Most patients received a myeloablative conditioning (MAC) containing 8 Gy (n = 47) and 12 Gy TBI (n = 11). Reduced-intensity regimens (RIC, 4 Gy TBI) were applied in 31 patients. Of note, patients receiving RIC were older than patients receiving MAC. The most common cancer types were non-squamous cell carcinomas (n = 14) after exclusion of a patient diagnosed with sarcoma within less than a year after TBI. The cumulative incidences of secondary malignancies and precancerous lesions were 8% (95%CI, 4-16), 14% (95%CI, 7-23), and 17% (95%CI, 9-27) at 10, 15 and 20 years, while the cumulative incidences of premature deaths were 59% (95%CI, 48-69), 59% (95%CI, 48-69), and 64% (95%CI, 49-76). In multivariate analyses, higher patient age at TBI was associated with lower rates of secondary malignancies/precancerous lesions, while higher patient age translated into a trend towards premature deaths (before patients could develop malignancies). Higher TBI doses, mainly applied in younger patients, translated into lower rates of secondary malignancies/precancerous lesions while lacking associations with mortality. Chronic GVHD requiring systemic immunosuppression was associated with premature deaths.
Conclusions: Although this study indicates an inverse relationship between TBI doses applied and treatment-related malignancies, confounding by competing risks is present. The age dependency may be explained by the fact that older patients had a lower life expectancy independent of malignancies, illustrating the pitfalls of competing risks.
Trial registration: The study was retrospectively registered.
Keywords: Acute myeloid leukemia; Allogeneic hematopoietic stem cell transplantation; Carcinogenesis; Low-dose radiotherapy; Secondary solid malignancies; Total body irradiation.
© 2024. The Author(s).