On thorotrast leucaemia. Evolution of clone of bone marrow cells with radiation-induced chromosome aberrations

Results are presented of chromosome studies of bone marrow cells from a 62-year-old woman. The patient had been given 40 ml of Thorotrast in connection with a neuro-radiological examination 34 years earlier. Clinically, the patient was now considered to be in an incipient myeloid leucaemic phase. Ninety-seven per cent of the bone marrow cells belonged to a clone with characteristic marker chromosomes induced by radiation. Few data are available on chromosome analysis of bone marrow cells from Thorotrast patients. Therefore, the results of the present study are compared with data from chromosome analyses of 32P-treated patients with polycythaemia vera, in whom large clones were found in the bone marrow. The results of chromosome analysis of bone marrow cells from the Thorotrast patient support previous hypotheses concerning the carcinogenesis in radiation-induced leucaemia in patients with polycythaemia vera, treated with 32P. In the latter patients, the clone cells are pressumed to represent cell populations with selective qualities, originating from radiation-damaged cells, which possibly possess an increased tendency to malignant transformation because of a more pronounced sensitivity to carcinogenic agents. The cells might also be potentially malignant and manifest themselves as leucaemic cells, if the patient's immunological defence mechanism is broken.