The new 2016 WHO
brain tumor classification defines different diffuse
gliomas primarily according to the presence or absence of IDH mutations ( IDH-mt) and combined 1p/19q loss. Today, the diagnosis of
anaplastic oligodendroglioma requires the presence of both IDH-mt and 1p/19q co-deletion, whereas
anaplastic astrocytoma is divided into IDH wild-type ( IDH-wt) and IDH-mt
tumors. IDH-mt
tumors have a more favorable prognosis, and
tumors with low-grade histology especially tend evolve slowly. IDH-wt
tumors are not a homogeneous entity and warrant further molecular testing because some have
glioblastoma-like molecular features with poor clinical outcome. Treatment consists of a resection that should be as extensive as safely possible,
radiotherapy, and
chemotherapy. Trials of patients with newly diagnosed grade II or III
glioma have shown survival benefit from adding
chemotherapy to
radiotherapy compared with initial treatment using
radiotherapy alone. Both
temozolomide and the combination of
procarbazine,
lomustine, and
vincristine provide survival benefit. In contrast, trials that compare single modality treatment of
chemotherapy alone with
radiotherapy alone did not observe survival differences. Currently, for patients with grade II or III
gliomas who require postsurgical treatment, the preferred treatment consists of a combination of
radiotherapy and
chemotherapy. Low-grade
gliomas with favorable characteristics are slow-growing
tumors. When deciding on the timing of postsurgical treatment with
radiotherapy and
chemotherapy, both clinical and molecular factors should be taken into account, but a more conservative approach can be considered initially in some of these patients. The factor that best predicts benefit of
chemotherapy in grade II and III
glioma remains to be established.