MYC and central nervous system cancer: We further examined the expression of pri-let-7a-1, pri-let-7f-1, pri-let-7d and MYC in three human GBM cell lines from high-grade tumors (U-373 MG, U-87 MG, and U-251 MG), one low-grade glioma (SW-1088), and a malignant neuroectodermal tumor (PFSK-1) by Real-Time PCR assays.