UBB and medullary thyroid gland carcinoma: These findings lend some support to the suggestion that the UBB, C-cells, and MTC all derive from the same cell type and may lend credence to the postulation that the UBB may be the stem cell of the thyroid and the cell of origin for tumors of C-cells, some thyroid epithelial tumors, and mixed thyroid follicular epithelial and medullary tumors.