Immunoglobin G / total antibody testing for SARS-CoV-2: a prospective cohort study of ambulatory patients and health care workers in two Belgian oncology units comparing 3 commercial tests

van Dam, Peter; Huizing, Manon; Roelant, Ella; Hotterbeekx, An; De Winter, Fien HR.; Kumar-Singh, Samir; Moons, Pieter; Amajoud, Zainab; Vulsteke, Christof; Croes, Lieselot; Janssens, Annelies; Berneman, Zwi; Prenen, Hans; Meuris, Leander; Berghe, Wim Vanden; Smits, Evelien; Peeters, Marc

BACKGROUND: Coronavirus disease (COVID-19) is interfering heavily with the screening, diagnosis and treatment of cancer patients. Better knowledge of the seroprevalence and immune response after Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection in this population is important to manage them safely during the pandemic. METHODS: 922 cancer patients, 100 non-cancer patients and 94 healthcare workers (HCW) attending the Multidisciplinary Oncology Unit of Antwerp University Hospital from 24(th) of March 2020 till 31(st) of May 2020, and in the Oncology Unit of AZ Maria Middelares Hospital Gent from 13(th) of April 2020 till 31(st) of May 2020 participated. The Alinity® (A; Abbott) and Liaison® (D; Diasorin) commercially available assays were used to measure SARS-CoV-2 IgG, while total SARS-CoV-2 Ig was measured by Elecsys® (R; Roche) RESULTS: In the overall study population IgG/total SARS-CoV-2 antibodies were found in respectively 32/998 (3.2%), 68/1020(6.7%), 37/1010 (3.7%) and of individuals using the A, D or R test. Forty six out of 618 (7.4%) persons had a positive SARS-CoV-2 polymerase chain reaction (RT-PCR) test. Seroprevalence in cancer patients (A:2.2%, D:6.2%, R:3.0%), did not significantly differ from that in non-cancer patients (A:1.1%, D:5.6%, R:0.0%), but was lower than the HCW (A:13%, D:12%, R:12%; respectively Fisher’s exact test p=0.00001, p=0.046, p=0.0004). A positive SARS-CoV-2 RT-PCR was found in 6.8% of the cancer patients, 2.3% of the non-cancer patients and 28.1% of the HCW (Fisher’s exact test p=0.0004). Correlation between absolute value of the different Ig tests was poor in the cancer population. Dichotomizing a positive versus negative test result, the A and R test correlated well (kappa 0.82 p McNemar test=0.344), while A and D, and R and D did not (respectively kappa 0.49 and 0.57; result significantly different p McNemar test=<0.0001 for both). The rate of seroconversion (>75%) and median absolute antibody levels (A: 7.0 vs 4.7; D 74.0 vs 26.6, R: 16.34 vs 7.32; all > P Mann Whitney test=0.28) in cancer patients and HCW with a positive RT-PCR at least 7 days earlier did not show any differences. However, none (N=0/4) of the patients with hematological tumors had seroconversion and absolute antibody levels remained much lower compared to patients with solid tumors (R: 0.1 vs 37.6, p 0.003; D 4.1 vs 158, p 0.008) or HCW (all p<0.0001). CONCLUSION: HCW were at high risk to be infected by SARS-CoV-2 during the first wave of the pandemic. Seroprevalence in cancer patients was low in the study period. Although Ig immune response in cancer patients with solid tumors does not differ from healthy volunteers, patients with hematological tumors have a very poor humoral immune response. This has to be taken into account in future vaccination programs in this population. SARS-CoV-2 antibody tests have divergent results and seem to have little added value in the management of cancer patients.