Increased Concentration of Transcobalamin I in a Patient with Metastatic Carcinoma of the Breast

A patient with metastatic carcinoma of the breast and increased plasma cobalamin binding capacity (about 50 nmol/1) is described. The binding protein was identified as transcobalamin I (TCI) by DEAE cellulose ion-exchange chromatography, Sephadex G200 gel filtration and agar gel electrophoresis. Although the total plasma cobalamin concentration (about 20 nmol/1) was elevated, the patient complained of neurological symptoms in accordance with a functional vitamin B12 deficiency. Hence, an inactivation of the coenzyme is suggested by the demonstration of considerable amounts of 5'-deoxyadenosylcobalamin bound to the plasma TCI. Both urinary excretion of FIGLU and methylmalonic acid were within the reference ranges. Reported cases of increased cobalamin binding in patients with nonhaematological malignancy are reviewed. Further investigations to characterize the function of the cobalamin dependent metabolic pathways are necessary to determine the importance of the increased transcobalamin binding in these patients.