Stereotactic Radiotherapy In Oligometastatic (Om) Gastrointestinal (Gi) Tumors: A Single Institution Retrospective Analysis

825 Background: Metastatic GI cancers are mainly treated with systemic treatment (ST), in selected patients (pts), surgery is considered depending on pts characteristics and institutional preferences. Stereotactic Radiotherapy (SRT) is a growing treatment option in such landscape aiming to improve local disease control and maximize ST results for oligometastatic pts. Methods: This is a single center retrospective study. Data were collected from sequential pts with GI tumors who underwent SRT for OM-GI cancers from May 2014 to July 2019. Information was collected on pts characteristics, primary site, clinical staging at diagnosis, sites undergoing SRT, whether there was progression after the first SRT, time between the first SRT and progression and the last follow-up date. Results: 381 pts underwent SRT in our center, of these, 75 pts had OM-GI tumors and underwent 120 courses of SRT. 50,7% were women, the median age at diagnosis was 60 years and the median follow-up was 36 months. 76% had colorectal cancer (CRC) being 26% from the right, 26% from the left colon and 30% were from the rectum, in 18% of the patients we could not determine sidedness. 35% already had metastatic disease at diagnosis. The lung was the site with largest number of lesions treated with SRT (50), followed by central nervous system (CNS) (42), bones (32), liver (29) and lymph nodes (16). After a median follow up of 15.3 months, 11% of patients were progression-free and only 24% had progressed on treated lesions. The median progression free survival following SRT was 4.5 months (0.6-45.8 range) for distant metastasis and was not achieved for treated sites. Conclusions: This retrospective study adds to the previous body of evidence supporting the use of SRT to improve GI cancer management. Detailed information on pts characteristics, pathology, toxicity and previous treatments will be presented.