During the dose escalation stage, all subjects will take GT0918 oral administration once daily on an empty stomach (fasted state) for 28 consecutive days. The first dosing cycle will be followed by at least a 7-day off-treatment period (for PK analysis); however, no off-treatment period will be scheduled between subsequent treatment cycles. If individual subjects on GT0918 show an objective response or stable disease (SD) according to Response Evaluation Criteria in Solid Tumors (RECIST v1.1) criteria and who is expected to benefit from continued treatment in the opinion of the investigator, they may continue to receive additional cycles of GT0918 in the absence of untoward or serious toxicity; however, no subject is permitted to start a subsequent cycle after each bi-monthly disease evaluation until it is confirmed that disease progression has not occurred. A subject without disease progression may continue GT0918 treatment with the approval of the investigator; treatment can continue until a subject experiences an intolerable adverse event (AE) or disease progression, withdraws consent or until termination of the study by the sponsor. A total of 6 cycles of GT0918 is planned; however, subjects without progressive disease (PD) have the option to continue with their assigned dose in a 6-month Extension Study. At the end of total 6 cycles of GT0918 or additional extension cycles, a post-treatment period of 4 weeks will commence that concludes with an end-of-study visit.