Reduced bone marrow uptake of indium-111 labelled monoclonal antibody after radiotherapy.

Uptake of indium-111 in bone marrow is seen in patients who have received 111In-labelled antibody. We report a case in which 111In uptake was not seen in the area of previous irradiation whereas fairly high uptake was noted in other bone marrow areas. 111In-labelled monoclonal antibody, which reacts with mucin, was injected into a patient with cancer of the sigmoid colon who had received radiotherapy for uterine cervical cancer 5 years previously. Marked accumulation of the antibody was observed in the tumour. Uptake of 111In in bone marrow was also seen except in the previously irradiated pelvic region. This phenomenon supports the idea that bone marrow uptake of 111In is the result of transchelation of 111In from antibody to transferrin.