Lymphoma and multiple myeloma in cohorts of persons exposed to ionising radiation at a young age.

There is limited evidence that non-leukaemic lymphoid malignancies are radiogenic. As radiation-related cancer risks are generally higher after childhood exposure, we analysed pooled lymphoid neoplasm data in nine cohorts first exposed to external radiation aged <21 years using active bone marrow (ABM) and, where available, lymphoid system doses, and harmonised outcome classification. Relative and absolute risk models were fitted. Years of entry spanned 1916-1981. At the end of follow-up (mean 42.1 years) there were 593 lymphoma (422 non-Hodgkin (NHL), 107 Hodgkin (HL), 64 uncertain subtype), 66 chronic lymphocytic leukaemia (CLL) and 122 multiple myeloma (MM) deaths and incident cases among 143,136 persons, with mean ABM dose 0.14 Gy (range 0-5.95 Gy) and mean age at first exposure 6.93 years. Excess relative risk (ERR) was not significantly increased for lymphoma (ERR/Gy = -0.001; 95% CI: -0.255, 0.279), HL (ERR/Gy = -0.113; 95% CI: -0.669, 0.709), NHL + CLL (ERR/Gy = 0.099; 95% CI: -0.149, 0.433), NHL (ERR/Gy = 0.068; 95% CI: -0.253, 0.421), CLL (ERR/Gy = 0.320; 95% CI: -0.678, 1.712), or MM (ERR/Gy = 0.149; 95% CI: -0.513, 1.063) (all p-trend > 0.4). In six cohorts with estimates of lymphatic tissue dose, borderline significant increased risks (p-trend = 0.02-0.07) were observed for NHL + CLL, NHL, and CLL. Further pooled epidemiological studies are needed with longer follow-up, central outcome review by expert hematopathologists, and assessment of radiation doses to lymphoid tissues.