IGFBP4 and glioblastoma: Using the polymerase chain reaction, GBM cell lines were found to express mRNA for IGFBP genes: IGFBP-1 in 42%, IGFBP-2 in 65%, IGFBP-3 in 97%, IGFBP-4 in 3%, IGFBP-5 in 74%, IGFBP-6 in 94%, and IGFBP-7 in 87% of glioma cell lines [14].