e13527 Background: The SARS-CoV-2 (COVID19) pandemic has had a huge impact on health care, leading to the declaration of a “state of alarm” in many countries. This situation has possibly conditioned the care of cancer patients, compromising hospitalization resources due to healthcare restraints. We aim to analyze the impact of the COVID19 pandemic on the hospitalization of cancer patients during the “state of alarm” in an Academic Hospital in Madrid, considered one of the most affected regions in the World during the first wave of the pandemic in Europe. Methods: Quasi-experimental study with similar controls collected in the same period of the previous year from cancer patients admitted to the Medical Oncology (MO) department of the Puerta de Hierro University Hospital in Madrid. Patients were selected from diagnoses coded by the ICD-10 obtained from discharge reports in the Admission Department. Cancer and viral pneumonia codes (excluding influenza) were analyzed. Admission to Internal Medicine (IM) department was also explored to describe hospitalization due to COVID19 pneumonia. We defined two groups: pandemic (03/14/20 - 06/20/20) and control (pre-pandemic) (03/14/19 - 06/20/19). Results: 74 cancer patients were admitted to MO department in 2020, while 162 admissions were recorded for the equivalent period in 2019 (- 54%). No differences were observed related to sex and age. In 2020, emergency and programmed admissions decreased by the same proportion, and no difference in mortality was observed. Admissions for all neoplasms decreased, but with higher magnitude in breast cancer. Viral pneumonia (no influenza) in cancer patients were mostly admitted to IM (96%) rather than MO department. 79 cases were identified in 2020, 22 in 2019 (p < 0.001), with a non-significant increase in mortality in patients with pneumonia: 25,3% in 2020 and 13,6% in 2019. Conclusions: The COVID 19 pandemic seriously impacted cancer hospitalization care, decreasing admissions to the MO department in half compared to the equivalent period. We observed a reduction in admissions through all neoplasias. Admissions due to viral pneumonia in cancer patients increased 3.5 times, mostly admitted to IM changing the dynamics of cancer hospitalization burden and compromising resources. A non-significant increase in mortality from viral pneumonia was observed. The analysis of hospitalizations through administrative data can allow better management of resources and facilitate rapid decision-making in a pandemic situation yet to be resolved.[Table: see text]