National Utilization of Imatinib in the Management of Resected Gastrointestinal Stromal Tumors.

ABSTRACT

BACKGROUND: Imatinib decreases recurrence risk and improves overall survival (OS) in localized gastrointestinal stromal tumors (GISTs); however, the extent to which patients receive appropriate treatment in the US has not been well characterized. METHODS: Patients with non-metastatic, resectable GIST were included in this study (National Cancer Database, 2010-2015). Those with a low-risk of recurrence were classified as receiving overtreatment or guideline-concordant treatment, while those with a high-risk of recurrence were classified as receiving undertreatment or guideline-concordant treatment. Multivariable logistic regression was used to determine factors associated with non-concordant treatment. The association between non-concordant treatment and OS was evaluated using multivariable Cox regression and propensity score matching. RESULTS: Among 3088 patients with high-risk GIST, 41% were undertreated, and among 3908 patients with low-risk GIST, 18.8% were overtreated. For patients with high-risk GIST, age > 60 years, African American race, and treatment at a community or comprehensive cancer program were associated with undertreatment. Among low-risk patients, small bowel primary, tumor size > 2 cm, and tumors with > 1 mitotic figure per 50 high-power fields were more likely to be overtreated. After propensity score matching, guideline-concordant therapy was associated with an 8.8% improvement in 5-year OS (81.9% vs. 73.1%, p = 0.002) for those with high-risk GIST and decreased risk of death (hazard ratio 0.63, 95% confidence interval 0.47-0.84). There was no statistically significant difference in survival for patients with low-risk GIST with the addition of imatinib overtreatment (overtreatment 93.9% vs. 89.6%, p = 0.053). CONCLUSIONS: Nearly 30% of GIST patients do not receive guideline-concordant treatment and future work is needed to understand the factors driving non-concordant treatment.