(P 221) SURGICAL OUTCOMES OF NEOADJUVANT THERAPY FOR GASTROINTESTINAL STROMAL TUMORS: A SINGLE INSTITUTION ANALYSIS

Objective: Gastrointestinal stromal tumors (GIST) are rare mesenchymal tumors which are often treated with tyrosine kinase inhibitors, such as imatinib, in both the neoadjuvant and adjuvant settings. Surgery is the mainstay of treatment. Neoadjuvant therapy (NAT) is often used to downsize tumors prior to surgery. However, there is little data regarding the effect of NAT on the extent of surgery performed or on postoperative outcomes. We analyzed the effect on NAT on postoperative complications as well as on the use of minimally-invasive and multi-organ resection.

Methods: We performed a retrospective analysis of 180 patients with pathologically confirmed GIST who underwent surgical resection at Fox Chase Cancer Center between 2004-2020. Demographic and clinical variables such as tumor size, tumor location, type of surgery, mutational status, and postoperative outcomes were collected. They were compared using both Mann-Whitney and Fisher’s exact tests. The association between NAT and post-operative complications was calculated using the Fisher’s exact test. Secondary outcomes including recurrence free survival (RFS) and overall survival (OS) were analyzed using Kaplan-Meier methods and Cox Proportional Hazards models.

Results: Of the 180 patients included, 74 received NAT, of which 90.5% received imatinib. The median duration of therapy was 5 months (mean = 8.7 months). 50 of the 74 NAT patients had mutations, with 71% with KIT mutations and 8.7% with PDGFRA mutations. NAT patients had a larger preoperative tumor size, with a mean size of 11.5 cm versus 5.28 cm in no-NAT (p< 0.000001). There were no significant differences in mean age, ASA status, or tumor location between the two groups . 83.7% of NAT patients underwent open surgery compared to 47.2% of no-NAT patients . 57 of 180 patients had multi-organ resection, the majority of which received NAT (OR=2.78, 95% CI: (1.36, 5.74), p=0.0025 ). The rate of any postoperative complication (as defined by ACS-NSQIP) was 31.1% in NAT vs. 15.1% no-NAT (Fisher’s exact test p=0.016, OR=2.52 (95% CI: 1.16,5.62)). This was not significant after multivariable logistic regression (p= 0.21). The most common complications were anastomotic leak (NAT) and surgical site infection/pneumonia (no-NAT). There was no statistically significant difference in OS or RFS between NAT and no-NAT patients after adjustments for confounders (median OS 124 versus 161 months, p=0.72; RFS p= 0.5).

Conclusion: Patients with larger GISTs were more likely to receive NAT and have higher rates of open and multi-organ resection. This is likely due to selection bias. Nonetheless, NAT was safe and effective without an increased risk of postoperative complications and with comparable OS and RFS. Further research is needed to assess the effect of NAT on these outcomes based upon mutational status and primary site, as well as in relation to trends over time.

CTOS2022_GIST_Table1.docx