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A455Objectives: Regorafenib is indicated in the treatment of locally advanced, nonresectable gastrointestinal stromal tumors (GIST) that did not respond to prior imatinib mesylate and sunitinib malate. The objective of this study is to evaluate the cost-effectiveness of regorafenib compared to standard care, since no other third line treatment is available, in metastatic/inoperable GISTs in Turkey. MethOds: A Markov model taking transitions of patients between three health states of "progression-free", "progressed" or "dead" was adapted to Turkish settings. Clinical transition inputs between health states and safety data were mainly derived from GRID study. Economic inputs were based on the experts' opinion addressing local treatments, routine monitoring and adverse event management algorithms. The incremental cost-effectiveness ratios (ICER) were calculated per quality adjusted life years (QALY) gained. Analyses were conducted from the Turkish Payer Social Security Institution perspective. All costs were calculated in Turkish Liras (TL). The cost effectiveness (CE) threshold defined by World Health Organization (WHO) for developing countries as ICER 1-3 fold of annual income per capita was calculated based on the Turkish 2014 annual income per capita of 10,404.00 USD and converted to TL using TL/USD currency rate of 2.28 (end of 2014). Results: Total costs associated with regorafenib and standard care are 22,902 and 1,692 TL, respectively. On the other hand, QALYs gained with regorafenib (2.714) was almost twice compared to standard care (1.402), with an ICER of 16,481 TL/year. This additional cost of treatment is below the lower margin of CE threshold that was 23,721.00 TL. cOnclusiOns: Regorafenib is a costeffective treatment option in metastatic/inoperable GISTs in Turkey. Compared to standard care, the additional cost of treatment is below the CE threshold.