Although the underlying mechanisms of fatigue have been studied in several disease conditions (Bower et al., 2002; Brola et al., 2007), the etiology, mechanisms, and risk factors remain elusive, and this symptom remains poorly managed. Fatigue is conceptualized as a multidimensional symptom which incorporates temporal, sensory, cognitive/mental, affective/emotional, behavioral, and physiological dimensions (Voss, et al., 2006). We recently observed increased levels of neutrophic factors (brain-derived neurotrophic factor (BDNF)), glial-cell line derived neurotrophic factor (GDNF) and synaptosomal-associated protein (SNAP) from the serum samples of fatigued prostate cancer men receiving external beam radiation therapy, suggesting that fatigue may be a component of depression and the N-methyl-D-aspartate (NMDA) receptors may be involved in fatigue intensification during cancer therapy. Ketamine is an NMDA receptor antagonist and has been reported to treat acute depression (Berman et al., 2000; Prommer, 2012; Aan Het Rot et al., 2012). Depression and cancer-related fatigue (CRF) are highly correlated during cancer therapy (Portenoy and Itri, 1999; Roscoe et al., 2002, Servaes et al., 2002, Aan Het Rot et al., 2012).