Adherence to Guidelines for Adjuvant Imatinib Therapy for GIST: A Multi-institutional Analysis

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Adjuvant imatinib therapy improves recurrence-free and overall survival following surgery for patients with high-risk GIST; however, the factors associated with use of adjuvant imatinib therapy are unclear, and adherence to adjuvant imatinib has not been investigated. We sought to determine the clinicopathologic predictors of therapy with adjuvant imatinib following surgical resection for GIST and to determine the utilization of adjuvant imatinib in patients who underwent surgical resection of primary GIST in 2009 or later as recommended by National Comprehensive Cancer network (NCCN) guidelines.

A multi-institutional cohort including 171 patients who underwent surgery for primary GIST at seven high-volume cancer centers in the USA and Canada between January 2009-December 2012 was used in this study. Receipt of adjuvant imatinib therapy was ascertained, and factors associated with imatinib therapy were analyzed.

Following surgery for primary GIST, tumor size (<5.0 cm: ref; 5.0-9.9 cm: odds ratio (OR) 2.36, 95 % confidence interval (CI) 0.74-7.55; >10.0 cm: OR 9.15, 95 % CI 2.28-36.75; p = 0.007), mitotic rate (≤5/50 mitoses per 50 high powered field [HPF]: ref; 6-10/50 HPF: OR 24.91, 95 % CI 3.64-170.35; >10/50 HPF: OR 5.80, 95 % CI 3.64-170.35; p < 0.001), and neoadjuvant therapy (OR 9.52; 95 % CI 2.51-36.14; p = 0.001) were associated with receipt of adjuvant imatinib therapy. Overall, 75 % of patients received appropriate treatment, 23 % of patients were undertreated, and 2 % of patients were overtreated as compared to NCCN guidelines. Adjuvant imatinib therapy was administered in only 53 % of patients for which the NCCN guidelines recommended adjuvant therapy.

The clinicopathologic factors associated with use of adjuvant imatinib therapy in patients following resection of primary GIST are consistent with established risk factors for recurrence. Adjuvant imatinib therapy remains underutilized in patients with intermediate and high-risk GIST and in patients who receive neoadjuvant therapy. Barriers to adjuvant imatinib therapy in this group of patients needs to be further explored.