Since December 2019, outbreak of COVID-19 caused by a novel virus SARS-Cov-2 has spread rapidly around the world and became a pandemic issue. Cancer patients seem to be at higher risk of infection and evolution to severe forms related to immunosuppression, according to the first published data from Chinese experience. However, the role of confounding factors such as age and smoking habits cannot be independently assessed. Supplementary data from a large retrospective Italian cohort suggest that the proportion of cancer patients with severe form of COVID-19 could be lower than expected. In addition, the proportion of asymptomatic SARS-Cov-2 infected cancer patients is unknown. Based on academic and expert's recommendations, most of cancer units have already modified cancer treatment during the pandemic, in order to limit the number of outpatient visits / inpatient admissions and then reduce or avoid cross infection of COVID-19, although the negative impact on patient's outcome (cancer recurrence or mortality) has not been established. Thus, a large screening for SARS-Cov-2 infection in treated cancer patients could help to: - Define an accurate prevalence of COVID-19 immunization in this population - Aggregate data on the relationship between clinical characteristics in cancer patients and COVID-19 risk. - Provide information about asymptomatic COVID-19 cases. - Organize effectively cancer units to separate infected and non-infected patients.

The RT-PCR gold-standard test for COVID-19 on nasal and pharyngeal swabs has limitations, as the test is not universally available, turnaround times can be lengthy, and reported sensitivities vary. It does not provide information about immunization status. Serological assays may be important for understanding the epidemiology of emerging SARS-Cov-2, including the burden and role of asymptomatic infections. Thus, the development of new devices or techniques for accurate diagnosis of SARS-CoV-2 infections, of fast and safe use, that could be spread in the local hospitals and clinics, would be a major advance for identifying and treating patients. In addition, information about the immunization of fragile people, such as cancer patients, could help to plan a safe strategy for anti-cancer treatment schedule and for the end of quarantine.

Inclusion Criteria:

1. Age ≥ 18-years old;
2. Patient treated for histologically proven cancer;
3. Patient that require at least one visit for anti-cancer treatment in a one-day outpatient care units
4. Patients that have previously been tested positive with a RT-PCR test from nasal swab that have been authorized to come to the hospital (after recovery or a 14-days quarantine period, according to local guidelines) can be included. 5. Patient willing and able to provide written informed consent/assent for the trial;

6. Patient affiliated with a health insurance system.

Exclusion Criteria:

1. Patient not able to give free consent

2. Patient not able to understand the protocol;

3. Patient not able to undergo the COVID-19 test

4. Vulnerable persons as defined by article L1121-5 - 8:

   1. Pregnant women, women in labour or breast-feeding mothers, persons deprived of their freedom by judicial or administrative decision, persons hospitalized without their consent by virtue of articles L. 3212-1 and L. 3213-1 and who are not subject to the provisions of article L. 1121-8
   2. Persons admitted to a social or health facility for reasons other than research

5. Adults subject to a legal protection order or unable to give their consent.