e18566 Background: Chronic myelomonocytic leukemia (CMML) is the most aggressive of chronic leukemias, with a short overall survival and a high transformation rate to acute leukemia. We investigated factors related to blastic transformation in Mexican population treated in a tertiary referral center Methods: Records of patients diagnosed with CMML between 2000-2015 were reviewed; patients with incomplete data were excluded. IBM SPSS Statics 21.0 software was used to perform statistical analysis. Results: 54 patients were included, with a median age of 71 years and an overall survival of 16 months. The rate of blastic transformation found was 33% (18 patients), with a time to progression of 9 (0-87) months. Comparing patients who didn’t underwent blastic transformation to those who did, those who progress to acute leukemia tend to be younger (58 vs. 71 years, p = 0.001), have a higher peripheral blood blast count (2% vs. 0%, p = 0.003), where more likely to have immature myeloid precursors circulating in peripheral blood (94% vs. 64%, p = 0.02). In multivariate analysis, age continued to be statistically significant (HR 0.97, 95% IC = 0.929-0.987). There where no statistical difference in the two groups regarding hemoglobin levels (8.2g/dL vs. 10.1g/dL) platelets count (115 X 109 vs. 93 X 109), absolute neutrophil count (5.83 X 109 vs. 5.18 X 109), absolute monocyte count (3.09 X 109 vs. 2.680 X 109), and bone marrow blast count (0 vs. 2%). Cytogenetic considered as high risk was not predictor of blastic progression. Intensive chemotherapy was offered to 7(38.9%) patients, with a complete response rate of 0%, the overall survival was 1.4 months (0-9). Conclusions: Contrary to other reported series;Mexican patients with CMML that progresses to overt acute leukemia were considerably younger, with a higher tumor burden and a very short overall survival. In this population, it is important to consider more aggressive treatments at diagnosis, focusing in high dose chemotherapy and hematopoietic stem cell transplantation in a short term ratter than watching and waiting or using agents that do not impact in disease natural history.