BDNF and cancer: Clinical application of Val66Met SNP as a prognostic/predictive marker for assessing the risk of developing cancer-related fatigue has several advantages: (1) SNP detection can be easily performed requiring only a small sample of blood; (2) genotypic marker detection is affordable, reliable, and yields reproducible results; (3) using the functional Val66Met polymorphism provides a more accurate assessment for brain BDNF and bypasses the aforementioned disadvantage of measuring serum/plasma BDNF concentrations, which is largely attributable to platelet-derived BDNF.