Benefit of adjuvant therapy in high-risk GIST: A large-scale real-world analysis of 2,166 patients (DEEPSARC study).

11533 Background: Real-life data on the impact of adjuvant treatment in GIST pts are limited. Methods: We conducted a retrospective study (Deepsarc) merging data from the NETSARC+ dataset of the French Sarcoma Group with the exhaustive health data from the national social security system (SNDS). Eligible pts were treated between January 1, 2012, and December 31, 2017 with localized GIST. The relation between overall survival (OS) and adjuvant therapy was studied univariate and multivariate, using different methods to address confounding factors. Results: A total of 2166 GIST pts were included, with a median age of 68.0 years (interquartile range (IQR): 58.0, 76.0), a sex ratio of 1.01. The two most common primary sites were gastric (1301, 60%) and small intestine (527, 24%). Median tumor size at diagnosis was 5.3 cm (IQR 3.6-8.1). Median mitotic count was 3.0 (IQR 1.0-5.0). According to Miettinen/AFIP classification, 331/1026 (32%) were high-risk, 192/1026 (19%) intermediate risk, and 503/1026 (49%) very low or low risk vs 490/912 (53%) high-risk, 193/912 (21%) intermediate risk, and 229/912 (25%) very low or low risk with Joensuu classification. From 2012 to 2017, the proportion of pts receiving adjuvant therapy remained remarkably stable at around one third of all GIST, with higher use in high-risk (70%; 231/331) than intermediate-risk (43%; 83/192) and low-risk pts (6%; 32/503). Pts receiving adjuvant therapy were younger (p<.001), with less comorbidities (p<.001), larger tumor (p<.001), higher mitotic count (p<.001), higher risk according to Miettinen/AFIP (p<0.001), or Joensuu (p<.001), higher rate of R1 resection (p=.019) and higher rate of tumor rupture (p=.001). Median follow-up was 5.0 years (4.8-5.2). Overall, the 5y OS rate was 81% [79-83%]. Regardless of risk, for the entire population, 5y OS rate of those receiving adjuvant therapy was 82% [79%-85%] and for those not receiving adjuvant therapy was 81% [78%-83%]. For both prognostic classifications, in univariate analysis, adjuvant therapy was associated with improved survival only for high-risk pts. Multivariate analysis propensity-score adjusted analyses for age, sex, social deprivation index, morbidity index, and tumor size (3 categories: ≤5/ 5-10/ >10 cm) highlights a benefit of adjuvant therapy for high-risk pts, according to both AFIP/Miettinen or Joensuu classifications (Table). No clear benefit was observed in intermediate-risk pts. Conclusion: This study confirms the benefit of adjuvant therapy for high-risk pts (according to AFIP/Miettinen or Joensuu), but not for other risk groups. Overall survival (risk of death) in high-risk GIST patients according to adjuvant therapy (reference = No adjuvant treatment), Deepsarc study (2012-2017), France. Risk classification N 1y HR* 95% CI** P -value Miettinen/AFIP 214 0.23 0.06 ; 0.92 0.017 Joensuu 312 0.49 0.24 ; 0.98 0.029 *HR = Hazard Ratio, **CI = Confidence Interval.