All patients (9 out of 9 cases) with COVID-19-related pneumonia were seropositive. 5 patients (41,6%) did not present any risk factor (41.6%), 3 were obese (25%), 3 (25%) were dyslipidemic (25%), 3 had chronic bronchopathy (25%) and 1 (8%) ischemic heart disease. Seroprevalence of SARS-COV-2-specific antibodies in cancer patients To date, there are no data on seroprevalence in the cancer population. an overall seroprevalence (IgG or IgM positive) of 31.4%. The probability of SARS-CoV-2 seropositivity was comparable between men and women, type of treatment and cancer stage. The probability of seropositivity was significantly higher in cancer patients with pneumonia compared with cancer patients without pneumonia (Odds Ratio (OR) 7.65 [95% confidence interval (CI) 1,85C31,58]). Interpretation Our results show a higher rate of SARS-CoV-2 antibodies in cancer patients than in the general population. The role of those antibodies in the immune response against the computer virus contamination is usually unclear. Keywords: COVID-19, SARS-CoV-2, Cancer patients, Seroprevalence, Antibodies, IgG and IgM Introduction Coronavirus disease in 2019 (COVID-19) Peretinoin caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has emerged as a global pandemic [1]. COVID-19 was first reported in Wuhan, China, in December 2019, among a group of individuals presenting with atypical pneumonia of unknown etiology [2]. Published data suggests that patients with a history of or active malignancy are at increased risk of contamination and developing COVID-19 related complications [3], [4]. Data from China have shown that cancer patients infected with COVID-19 are at 3.5 times the risk of requiring mechanical ventilation or intensive care unit (ICU) admission, compared to the general population [3]. In a recent cohort study, 928 cancer patients (39% were on active anticancer treatment, and 43% had active cancer) were analyzed, with a 30-day all-cause mortality of 13%, associated with general risk factors and risk factors unique to patients with cancer [1]. Seroprevalence surveys are of utmost importance to assess the proportion of the population that has already developed antibodies against the computer virus and might potentially be guarded against subsequent contamination [5]. SARS-CoV-2 IgM/IgG assessments have been developed for the diagnosis and management of COVID-19 patients, identifying convalescent cases and Peretinoin sero-epidemiological surveillance [6]. In patients infected with SARS-CoV-2, IgM antibodies are detectable around 7?days postinfection and IgG antibodies usually take 2?weeks to develop [7]. Patients with cancer and COVID-19 have a low prevalence of IgG antibodies to SARS-CoV-2. Liu T et al [8] found that only 72.5% had IgG Peretinoin antibodies to SARS-CoV-2 after 21?days post-symptom onset, much lower than patients without cancer. Currently, the role of IgG antibodies to SARS-CoV-2 in the immune response against the virus infection is unclear. It is hard to interpret the finding of the low prevalence of IgG antibodies to SARS-CoV-2 in cancer patients. Since all the above serological tests have been developed rapidly and SCC1 under urgent market demands, they are poorly validated with clinical samples in everyday practice. Within several studies, these tests show divergence in sensitivity and specificity that may deviate from what the manufacturers report. Recent meta-analysis concludes that all methods yield high specificity with some of them (Enzyme-linked immunosorbent assay (ELISA) and Lateral Flow Immunoassays (LFIA)) reaching levels around 99% [9]. It is unknown whether there is a difference in the prevalence of antibodies to SARS-CoV-2 between cancer patients and other patients in the COVID-19 era. To date, the published data has analyzed the seroprevalence of COVID-19 infection in the general population [10], [11], [12], with values ranging between 1.8% and 10.9%, without specifying the cancer population. Since the start of the alert by COVID-19 and until June 21 st, 2020 (health alert center), 246,272 cases of SARS CoV-2 infection have been diagnosed by PCR in Spain [1], with 71,223 cases (28.92% cases registered in the country) diagnosed in the region of Madrid (Spain) [13]. ENE-Covid19 is a large population-based seroepidemiological longitudinal study, whose objectives Peretinoin are to estimate the prevalence of SARS-Cov2 infection by determining antibodies against the virus in Spain and evaluating its temporal evolution. The results presented in the first.