Diffuse low-grade gliomas (DLGG) (or WHO grade II gliomas, Louis et al., 2007) are rare tumors, with an incidence estimated at 1/105 person-year (Ostrom et al., 2015). They affect young people in their thirties or forties (Capelle et al., 2013). DLGG are characterized by a continuous growth and an unavoidable anaplastic transformation (Mandonnet et al., 2003). Epilepsy is the main presenting mode while neurological deficits are rare at diagnosis due to the brain plasticity allowed by the usually slow growth speed of these tumors. However, frequent alterations in cognitive functions (including mostly memory, executive functioning, and attention) have been described (Racine et al., 2015). The prognosis of DLGG is variable (Pignatti et al., 2002) and overall survival (OS) ranges from 5 years to 15 years according to several factors, including the tumor phenotype, the isocitrate dehydrogenase (IDH) mutation and the 1p19q codeletion, the tumor volume at diagnosis, and the tumor spontaneous growth speed (Capelle et al., 2013).~The prognostic impact of the extent of surgery has now been well demonstrated (Jakola et al., 2012; Duffau 2016) and surgery is now the first treatment option (Soffietti et al., 2010). In unresectable DLGG or in patients with a progressive disease after surgery (with no possibility of a second surgery), several treatment options have been investigated, including radiation therapy (RT) and chemotherapy, but to date the timing and choice of treatment remains controversial. RT can be efficient in DLGG, however, the EORTC 22845 phase III trial found that early RT has no impact on OS compared to late RT, despite an increased progression-free survival (PFS) (van Den Bent et al., 2005). Moreover, some evidence of late decreased neurocognitive functioning has been consistently reported following RT (Klein et al., 2002; Douw et al., 2009). Because of this potential neurotoxicity and the absence of a benefit on OS of early RT, many neuro-oncological teams now only offer RT to patients with a progressive disease after chemotherapy.~Temozolomide (TMZ), an orally administered drug, was shown to be efficient in DLGG, with a good tolerance (Hoang-Xuan et al., 2004; Ricard et al., 2007). However, data regarding the impact of TMZ on neuro-cognitive functioning and quality of life (QoL) are scarce. Only few studies have performed an extensive, longitudinal assessment of cognition and QoL in DLGG patients receiving TMZ (Liu et al., 2009; Blonski et al., 2012; Klein, 2015). Moreover, many studies did not take into account the other factors that can alter the cognition such as the tumor itself, the surgery, seizures, anti-epileptic drugs, but also the premorbid level of cognition and the psychopathological affects such as depression, anxiety, or anger (Klein, 2015). To date, there is only few data on these psychopathological aspects in DLGG patients, either at diagnosis or following chemotherapy or RT.~Studying QoL in patients DLGG receiving TMZ is complex because of the multiples interactions between tumor characteristics, neurocognitive functioning, treatments, environment and psychopathological context in which these patients experience symptoms. It is, however, important to accurately evaluate these aspects in consideration of the young age, generally preserved QoL at the time of diagnosis, possible implications of the disease on the professional (DLGG patients are often still active), social and familial domain, and relatively long survival of these patients. In the absence of a curative treatment for DLGG, preserving patients' QoL is indeed a major goal.
Studying QoL in patients DLGG receiving TMZ is complex because of the multiples interactions between tumor characteristics, neurocognitive functioning, treatments, environment and psychopathological context in which these patients experience symptoms. It is, however, important to accurately evaluate these aspects in consideration of the young age, generally preserved QoL at the time of diagnosis, possible implications of the disease on the professional (DLGG patients are often still active), social and familial domain, and relatively long survival of these patients. In the absence of a curative treatment for DLGG, preserving patients' QoL is indeed a major goal.