TCN1 and cancer: Several mechanisms can lead to high B12 levels: (i) excessive intake or administration, (ii) release from reservoirs (such as from the liver in cases of hepatic insufficiency and/or metastases), (iii) decreased vitamin B12 clearance, in cases of renal or hepatic insufficiency, (iv) an increase in vitamin B12 transporting proteins (transcobalamin or haptocorrin) produced by cancer cells, and (v) immune complexes, where vitamin B12 bound to immunoglobulins can falsely elevate measured levels [1,87].