Carcinogenic risk of retained arsenic after successful treatment of acute promyelocytic leukemia with arsenic trioxide: a cause for concern?

surrounding the excised cancer exceeded that in the normal thyroid tissue of four other patients with thyroid cancer who had no known exposure to arsenic, and was considered to refl ect retention of arsenic for 10 years after completion of ATO administration that could have promoted the development of thyroid cancer. Th ere are a number of questions as to the extent to which these observations provide evidence of an unequivocal link between tissue retention of arsenic after ATO therapy and an increase in cancer risk. Th e arsenic concentration in thyroid tissue of the unexposed control subjects was highly variable, ranging from virtually negligible to approximately half that in the ATO trioxide treated patient, which in such a limited number of patients prevented statistically signifi cant confi rmation of a diff erence between arsenic concentrations in thyroid tissue of the patient and the subjects who had not