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Background: Stromal tumors of the digestive tract are uncommon malignant diseases, are subclassified as leiomyosarcomas and Gastrointestinal Stromal Tumors (GIST) depending on the molecular expression of tyrosine kinase receptor KIT (CD117). GISTs represent 1% of malignant tumors affecting this anatomical site. Localized tumours diseases are reasonably well controlled by surgical resection and several criteria define the need for adjuvant therapy. In the case of metastatic disease a poor prognosis has been reported with systemic treatment based on chemotherapy. Recently, significant advances have been shown since tyrosine kinase inhibitors (TKIs) were introduced, with median overall survival close to 5 years. Unfortunately in Mexico, even though the therapy has been long used there are no published data of the experience in the treatment of these tumors. Methods: We used an electronic data base to obtain clinical, radiological and histological data of patients diagnosed with GIST and treated in the oncological center of the Mexican Institute of Social Security, patients were subclassified by stage, symptoms at diagnosis as well as the initial and subsequent systemic treatment. Finally we made an analysis for progression free survival and overall survival identifying prognostic factors. Results: We obtained information of 71 patients with metastatic, non-resectable or recurrent GIST, treated with a TKI, we observed a predominant relation for women (60.4%) with median age of 58 years.Stage at diagnosis was predominantly metastatic (46.5%), most frequently affected sites were lung, liver and retroperitoneum. Median progression free survival was 30.6 months and overall survival was 81.3 months.All patients were initially treated with imatinib at a dose of 400 mg per day. Treatment was well-tolerated in most cases. Conclusions: Metastatic GIST evaluated in our center shows a different affection in gender and age, and our population shows a different response to TKIs, compared to those reported in other series with superior overall survival. Poor prognosis is associated with lung affection. Biological studies will be started for the molecular evaluation of these tumors.

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e13104 Background: In Mexico, The Instituto Mexicano del Seguro Social (IMSS) is a tripartite contribution which provides care to more than 74 million beneficiaries, which represents more than 50% of the general population of the country. Although Mexican breast cancer statistics have been reported, it is imperative to know the updated statistics on the epidemiology in our Institution. The aim of this study is to describe the survival outcomes and the clinical-pathological characteristics of patients with breast cancer. Methods: Records of breast cancer patients treated at the Oncology Hospital from Centro Medico Nacional Siglo XXI of IMSS, from January 2012 to December 2020 were included. We analyzed clinical and demographic characteristics of the population, as well as survival outcomes at 5-years. Results: A cohort of 5,264 patients was included. Median follow up was 54.9 months. Forty-three percent (n = 2,274) were diagnosed in early-stage breast cancer (I–IIA), 43.1% (n = 2,269) in stages IIB-III, and 7% (n = 383) in stage IV. The most common immunophenotype was hormone receptor (HR) positive, HER2-negative (70.8%, n = 3,726). HER2-positive represents 19.3% (n = 1011), among HR-positive were 12.4% (n = 650) and HR-negative, 6.9% (n = 361). 527 patients (10.1%) were triple negative. At 5-years, disease-free survival was 74.9% (95% CI, 73.5 to 76.3) and overall survival was 90.4% (95% CI, 89.4 to 91.3). High histologic grade (HR 1.51; 95% CI, 1.33 to 1.7; p < 0.001) and lymphovascular invasion (HR 1.84; 95% CI, 1.62 to 2.1; p < 0.001) were associated with higher risk of recurrence. Adjuvant chemotherapy was significantly associated to a 42% reduction in the risk of recurrence, HR 0.58 (95% CI, 0.49 to 0.69; p < 0.0001), and 54% in the risk of death, HR 0.46 (95% CI, 0.33 to 0.63; p < 0.0001) in stage III. Lobular histology was also associated with worse survival, HR 1.41 (95% CI, 1.069 to 1.859; p = 0.015). Conclusions: An update of breast cancer Mexican patients treated at IMSS is presented. We highlight the impact of adjuvant treatment and pathological risk factors for recurrence and death. This work can contribute to evaluate areas for improvement in management and outcomes in our population.

514 Background: Gastroenteropancreatic neuroendocrine tumors (GEP NET´s) are infrequent tumors, with a variety of symptoms depending of the kind of peptide they secrete as well as the affected organs. Long acting somatostatin analogues have shown an adequate rate of symptom control in functional tumors, they also have demonstrated antiproliferative effect, which is translated in a significant improvement of progression free and overall survival Methods: In this retrospective analysis of patients with metastatic GEP NET treated with long acting somatostatin analogues as first line, treated between 2005 and 2015, we evaluated clinical and pathological features, symptoms, disease control and survival adjusted with OMS classification Results: Our cohort included 95 patients with a mean age of 53 years. Primary affected sites were midgut (29.4%), followed by pNET (17.%), stomach (14.7%), and primary unknown in 14%. 20% of cases were functional tumors with diarrhea as the most common symptom in 70% and flushing in 50%. Considering the whole cohort the most prevalent symptom was abdominal pain in the 50% of cases. The OMS classification showed low grade tumors in 65% and 35% intermediate grade. Most common metastatic organ sites were; liver only 35%, liver and other 30%, peritoneum 10% and lymph nodes in 6%, non-specified sites in 19%. Somatostatine analogues used in first line were octreotide in 80% and lanreotide in 20%. Survival results demonstrated a progression free survival for the whole cohort of 84months. No differences between lanreotide and octreotide were observed. Conclusions: This study represents the first Mexican cohort of patients with GEP NET’s treated with somatostatin analogues with a long follow up.