Objective: To investigate the association of the single nucleotide polymorphism (SNP) rs2252784 in the protein tyrosine phosphatase receptor type B (PTPRB) gene with familial glioblastoma multiforme (GBM). Material and Methods: Genomic DNA was extracted from the peripheral blood samples of 2 sibling GBM patients, their 6 family members, 2 formalin-fixed paraffin-embedded (FFPE) tumor tissues. A 400 bp region was amplified and the restriction fragment length polymorphism (RFLP) technique was used to identify the rs2252784 SNP in exon 2 of the PTPRB gene. The GBM cell line T98G was used to validate the findings obtained from the tumor samples. Results: The analysis of DNA obtained from the blood samples of both GBM patients showed a wild-type (WT) genotype. However, the results of the PCRRFLP analysis from FFPE tumor tissues showed that the first patient (proband) was heterozygous, and his sibling was homozygous for the rs2252784 variant. Discordant results between SNP analyses of the DNA samples isolated from the blood and FFPE tumor tissue were observed. The family members of the patients had either homozygous WT or heterozygous variants. Conclusion: The rs2252784 SNP was present in the tumor DNA of the patients but not in the DNA samples obtained from blood. This discrepancy might be the result of oncogenic DNA alterations associated with tumor formation. Paired analysis of tumors and blood samples from patients and patient-matched normal blood samples from GBM-affected families might provide additional insights into the underlying genetic alterations that occur during the development of a tumor in familial GBM.