Increased risk of myeloid leukaemia in patients with ankylosing spondylitis following treatment with radium-224

Objective. To investigate long-term health effects in AS patients treated with 224 Ra.Methods. A prospective epidemiological study has been carried out on 1471 AS patients treated with repeated intravenous injections of 224 Ra between 1948 and 1975. These patients have been followed together with a control group of 1324 AS patients not treated with radioactive drugs and/or X-rays. Numbers of malignancies expected in a normal population were computed from German and Danish cancer registry data.Results. After a mean follow-up time of 26 yrs in the exposed group or 25 yrs in the control group, causes of death have been ascertained for 1006 exposed patients and 1072 controls. In particular, 19 cases of leukaemia were observed in the exposure group (vs 6.8 cases expected, P < 0.001) compared to 12 cases of leukaemia in the control group (vs 7.5 cases expected). Further subclassification of the leukaemia cases demonstrated a high increase of myeloid leukaemia in the exposure group (11 cases observed vs 2.9 cases expected, P < 0.001), especially a high excess of acute myeloid leukaemias (7 cases observed vs 1.8 cases expected, P = 0.003), whereas in the controls the observed cases are within the expected range (4 myeloid leukaemias vs 3.1 cases expected).Conclusions. The enhanced leukaemia incidence in the exposed group is in line with results from experiments in mice injected with varying amounts of the bone-seeking α-emitter 224 Ra. In these studies, in animals exposed to lower doses of 224 Ra, i.e. at doses lower than those found to induce osteosarcomas, an increased risk of leukaemia was observed.