This Phase 2 study is conducted to assess the efficacy and safety of DS-1001b in patients with chemotherapy- and radiotherapy-naive IDH1 mutated WHO grade II glioma.

Inclusion Criteria:

• Has a histopathologically documented IDH1 mutated WHO grade II glioma according to the 2016 WHO classification.
• Has confirmed IDH1 mutation at the R132 locus by testing at the central laboratory conducted during the screening period.
• Has no prior anticancer treatment (including chemotherapy and radiotherapy) for glioma except craniotomy or biopsy.
• Has at least 1 measurable and non-enhancing lesion.
• Has an interval of at least 90 days from the latest surgery.
• Has no sign of malignant transformation including the appearance of enhancing lesions and/or rapid growth of non-enhancing lesions.
• Has an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 to 1.

Exclusion Criteria:

• Has had a histopathological diagnosis of WHO grade III or IV glioma.
• Has had a contrast enhancing lesion on brain MRI.
• Has received a prior treatment with any mutant IDH1 inhibitor.
• Has received other investigational products within 28 days before the start of the study drug treatment.
• Has an active infection requiring systemic treatment.
• Has multiple primary malignancies.
• Has a history of clinically significant cardiac disease.
• Is a pregnant or lactating woman.

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.