OBJECTIVES: Gastrointestinal stromal tumors (GIST) are rare but costly tumors with an estimated incidence of 1.5/100 000/year in Europe. Granting reimbursement requires locally adapted cost effectiveness data in Turkey. This study was conducted to estimate the costs-of disease and direct cost components of metastatic/inoperable GISTs that did not respond to prior imatinib mesylate and sunitinib malate.  METHODS: Bayer Turkey Market Access team organized an “expert panel” composed of oncologists to discuss the local treatments, routine monitoring and adverse event management algorithms in metastatic/inoperable GIST patients. The panel reviewed the global and local literature and guidelines and also discussed the spectrum of frequently performed local clinical practices. All cost components, including medications, hospitalization, out-patient follow-up procedures and rehabilitation services were reviewed. End of 2014 local prices for medications and procedures were used as sources. Based on the answers of the physicians, the cost of healthcare resources regarding the conditions described were calculated from the perspective of the Turkish payer (SSI – Social Security Institution). RESULTS: In metastatic/inoperable GIST patients, treatment should be continued indefinitely, since treatment interruption is generally followed by relatively rapid tumor progression in almost all cases, even when lesions have been previously surgically excised. The cost of routine monitoring in the follow-up of metastatic/inoperable GIST patients was estimated to be 62.40 TL/month during progression-free and post-progression periods, while it was 490.00 TL/month during the terminal phase. The greatest cost is estimated for hospitalization in the intensive care unit ranging from 200.00 to 800.55 TL per incident. The most common adverse reactions were listed as hand and foot skin reaction (4%) and diarrhea (6.7%).    CONCLUSIONS: The costs of the disease, which therefore are quite high, estimated here will provide the most reliable data reflecting current figures to Public Stakeholders. Despite these high expenditures, those treatments’ efficacy is not clinically proven.