In our case of CMTC, positivity for CD117 (with negativity for CK5/6, p63, and p40) would identify a tumor population devoid of terminal differentiation (stem cell type); this fact also agrees with the negativity for markers of complete follicular differentiation (negativity for NIS, thyroglobulin, and thyroglobulin mRNA), as well as complete intestinal differentiation (negativity for CK20, CEA and SATB2). The gene discussed is KRT5; the disease is neoplasm.