SARS-CoV-2 antibody seroprevalence in cancer patients on systemic antineoplastic treatment in the first wave of the COVID-19 pandemic in Portugal

At the time of the first wave of the COVID-19 pandemic cancer patients were considered to be at high risk of serious illness and had a higher exposure risk since they needed frequent and non- deferrable hospital visits. Serologic tests were not routinely used and seroprevalence in this population was unknown.

A single-center cross-sectional study was developed to determine the seroprevalence of anti- SARS-CoV-2 antibodies (Abs) in cancer patients undergoing systemic antineoplastic treatment. One hundred patients were consecutively recruited in a two-week period (6th to 20th May, 2020) and serum samples were tested for the presence of IgM and IgG Abs directed against both spike and nucleocapsid SARS-CoV-2 proteins in two distinct timepoints (at recruitment and four to eight weeks later). IgG positive results were subject to confirmation, in the same serum sample, using two distinct assays.

At the time of the first study visit, no patient had a previously confirmed diagnosis of COVID-19, one reported previous contact with a COVID-19 patient and all had a baseline SARS-CoV-2 negative RT-PCR. Two patients tested positive for SARS-CoV-2 IgG in the first study visit, which was not confirmed in either of the two confirmatory assays. Seventy-two patients were tested at the second study visit, all with negative IgG test. IgM was persistently positive at both study visits in one patient and was positive in another patient at the second study visit, both with negative RT-PCR and serum IgG. No patient tested RT-PCR positive within the study timeframe.

No evidence of prior or acute SARS-CoV-2 infection was documented in this cohort of cancer patients undergoing systemic treatment and no additional exposure risk was documented compared to general population seroprevalence studies. The study was inconclusive regarding the role of SARS-CoV-2 serology in cancer patients in the early phase of the pandemic. This study did show that, with adherence to recommended preventive measures, it was safe to maintain systemic cancer therapy.