“…There are case reports of EP with a high Mib-1 proliferation index 15 or larger than 2 cm 9 as well as reports of chordoma smaller than 2 cm, 10, 13 with a low Mib-1 proliferation index, 8,16 or no associated bone involvement. 2,8,[17][18][19] Since EP and chordoma both derive from embryonic notochordal cells, share common ultrastructural characteristics as well as cell surface markers, and contain the same physaliphorous cells, [20][21][22] no distinguishing and specific pathologic marker is currently available. EP and chordoma are so similar on pathologic analysis that notochord remnant lesions may often be given an erroneous pathologic diagnosis of chordoma.…”