Background It has been assumed that cancer patients, especially those undergoing chemotherapy, are at increased risk for infection and severe illness from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) compared to the general population. After the first alert message from the local healthcare service, a series of drastic measures were taken at our outpatient clinic to contain the spread of coronavirus disease 2019 (COVID-19). Methods In this retrospective study, all consecutive cancer outpatients completed a baseline SARS-CoV-2 test via real-time polymerase chain reaction (RT-PCR) from 15 March to 26 May 2020. In the later phase, after the peak of the pandemic, patients as well as healthcare workers were tested for anti-SARS-CoV-2 IgG antibodies. Results Between 15 March and 26 May 2020, 0.78% (N = 5/640) cancer patients tested positive for SARS-CoV-2 by RT-PCR. Between 22 June and 17 July 2020, anti-SARS-CoV-2 IgG antibodies were detected in 2 out of 250 (0.8%) cancer patients and 2 out of 36 (5.5%) healthcare workers. In only 1 out of 4 cancer patients with confirmed COVID-19 infection, could SARS-CoV-2 antibodies be detected. Conclusion Our findings suggest that the majority of our patients and healthcare workers had not been infected with SARS-CoV-2 and rapidly implemented measures were effective. Maintenance of preventive Data availability The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.