Ionizing radiation exposure after allogeneic hematopoietic cell transplantation

Severity of Chronic Graft-versus-Host Disease and Late Effects Following Allogeneic Hematopoietic Cell Transplantation for Adults with Hematologic Malignancy

The study aimed to determine the association of chronic graft-versus-host disease (cGVHD) diagnosis and severity with the development of subsequent neoplasms (SN) and nonmalignant late effects (NM-LE) in 2-year disease-free adult survivors following hematopoietic cell transplantation (HCT) for a hematologic malignancy. To do so, we conducted a retrospective analysis of 3884 survivors of HCT for hematologic malignancy in the Center of International Blood and Marrow Transplant Research database. We conducted a landmark analysis at the 2-year post-transplantation date, comparing first SN and NM-LE in survivors with and without cGVHD. The cumulative incidence (CuI) of SN and NM-LE were estimated through 10 years post-HCT in both groups, with death or disease relapse as a competing risk. Cox proportional hazards models were used to evaluate the associations of cGVHD and its related characteristics with the development of SN and NM-LE. The estimated 10-year CuI of SN in patients with GVHD (n = 2669) and patients without cGVHD (n = 1215) was 15% (95% confidence interval [CI], 14% to 17%) versus 9% (7.2% to 11%) (P < .001). cGVHD by 2 years post-HCT was independently associated with SN (hazard ratio [HR], 1.94; 95% CI, 1.53 to 2.46; P < .0001) with a standardized incidence ratio of 3.2 (95% CI, 2.9 to 3.5; P < .0001). Increasing severity of cGVHD was associated with an increased risk of SN. The estimated 10-year CuI of first NM-LE in patients with and without cGVHD was 28 (95% CI, 26% to 30%) versus 13% (95% CI, 11% to 15%) (P < .001). cGVHD by 2 years post-HCT was independently associated with NM-LE (HR, 2.23; 95% CI, 1.81 to 2.76; P < .0001). Multivariate analysis of cGVHD-related factors showed that increasing severity of cGVHD, extensive grade, having both mucocutaneous and visceral involvement, and receiving cGVHD treatment for >12 months were associated with the greatest magnitude of risk for NM-LE. cGVHD was closely associated with both SN and NM-LE in adult survivors of HCT for hematologic malignancy. Patients identified as having more severe involvement and both mucocutaneous and visceral organ involvement may warrant enhanced monitoring and screening for SNs and NM-LEs. However, caution is warranted when interpreting these results, as patients with cGVHD may have more vigilant post-transplantation health care and surveillance for late effects.

Radiation and leukaemia: Which leukaemias and what doses?

The cause(s) of most cases of leukaemia is unknown. Save for several rare inherited disorders the most convincingly-identified causes of leukaemia are exposures to ionizing radiations, to some chemicals and to some anti-cancer drugs. Data implicating ionizing radiations as a cause of leukaemias come from several sources including persons exposed to the atomic bomb explosions in Japan, persons receiving radiation therapy for cancer and other disorders, persons occupationally exposed to radiation such as radiologists and nuclear facility workers, cigarette smokers, and others. Although ionizing radiations can be a cause of almost all types of leukaemias, some are especially sensitive to induction such as acute and chronic myeloid leukaemias (AML and CML) and acute lymphoblastic leukaemia (ALL). Whether chronic lymphocytic leukaemia can be caused by radiation exposure is controversial. The mechanism(s) by which ionizing radiations cause leukaemia differs for different leukaemia types. I discuss these issues and close with a hypothesis which might explain why haematopoietic stem cells are localized to the bone marrow.