Table 1. Drug Acquisition and Treatment Cost Inputs.

Variable	First-line treatment					Fourth-line treatment
	Avapritinib	Imatinib	Sunitinib	Regorafenib	Nilotinib	Avapritinib	Regorafenib	Nilotinib	Sorafenib	Pazopanib
Duration of treatment, moa	29.5	6.4	6.4	6.4	6.4	3.7	1.8	1.8	1.8	1.8
Drug acquisition cost per month, $b	32 000	1404	15 023	19 493	27 557	32 000	19 493	27 557	20 148	13 913
Adverse event cost per month, $c	407	204	180	219	51	588	219	161	56	389
Monitoring cost per month, $d	176	191	195	176	189	176	176	189	183	189

Abbreviations: GIST, gastrointestinal stromal tumors; PDGFRA, platelet-derived growth factor receptor alpha.

^a The median progression-free survival associated with avapritinib for treatment of PDGFRA exon 18 was not reached in the most recent data cutoff for PDGFRA exon 18. In the absence of PDGFRA exon 18–specific median progression-free survival, the median progression-free survival was assumed to be the same as for PDGFRA exon 18 D842V, for which more recent data are available.²⁰ For first-line treatment, duration of treatment was assumed to be equal to median progression-free survival.^2,21,22

^b Costs presented in this table do not include the post-progression costs associated with each treatment line. Avapritinib drug acquisition for fourth-line treatment was assumed to be the same as for PDGFRA exon 18. Drug acquisition costs per month were extracted from the IBM Micromedex 2020.²³

^c Adverse event incidence rates were converted to monthly incidence rates using the formula: monthly rate = −ln (1 − [fraction of patients with AE/time in months]). Adverse event rates were obtained from prescribing information or clinical trials for GIST. For avapritinib, in accordance with the prescribing information, 44% of individuals were receiving treatment for at least 12 months and 56% for at least 6 months; a median duration of exposure of 6 months was assumed for avapritinib on a conservative basis. Adverse event costs are calculated as the median hospitalization cost from HCUPnet.²⁴

^d Monitoring requirements were calculated based on National Comprehensive Cancer Network–recommended testing procedures for GIST, with treatment-specific adaptations based on monitoring recommendations reported in the respective prescribing information. Monitoring costs were extracted from the 2019 Centers for Medicare & Medicaid Services Clinical Laboratory Schedule and the 2019 Centers for Medicare & Medicaid Services Physician Fee Schedule.^25,26