Initially diagnosed as chordoid meningioma at the 1st resection, with diffuse expression of NHERF1 microlumens and a low Ki-67 proliferation index (Figure 4B), the 3rd resection showed sarcomatous transformation of the recurrent tumor, absence of NHERF1 microlumens, and high mitotic and Ki-67 proliferation indices (Figure 4C). The gene discussed is MKI67; the disease is Chordoid Meningioma.