Caveats and Pitfalls of SOX1 Autoantibody Testing With a Commercial Line Blot Assay in Paraneoplastic Neurological Investigations.

Raquel Ruiz-García,Josep Dalmau,Marta Español-Rego,Milagros García-Ormaechea,Francesc Graus,Isabel Illa,Lidia Sabater,Luis Querol,Eugenia Martínez-Hernández

doi:10.3389/fimmu.2019.00769

Abstract

SOX1 autoantibodies are considered markers of small cell lung cancer (SCLC) and paraneoplastic neurological syndromes (PNS) and are usually determined by commercial line blot in many clinical services. Recent studies suggested that SOX1 autoantibodies also occur in patients with neuropathies unrelated to SCLC, questioning the value of SOX1 autoantibodies as paraneoplastic biomarkers. Here, we compared the specificity and sensitivity of a commercial line blot (Euroimmun, Lübeck, Germany) with those of an in house cell-based assay (CBA) with HEK293 cells transfected with SOX1. Overall, 210 patients were included in the study, 139 patients with polyneuropathies without SCLC, and 71 with disorders associated with SOX1 autoantibodies detected with the in-house CBA. Forty one of these 71 cases had been referred to our laboratory for onconeuronal antibody assessment and 30/71 were patients with known PNS and SCLC. None of the patients with polyneuropathies had SOX1 autoantibodies by either line blot or CBA (specificity of the immunoblot: 100%; 95%C.I.: 97.8–100). Among the 71 patients with CBA SOX1 autoantibodies, only 53 were positive by line blot (sensitivity: 74.6%; 95%C.I.: 62.9–84.2). Lung cancer was detected in 37/41 (90%; 34 with SCLC) patients referred for onconeuronal antibody assessment and 34 of them also had a PNS. Our study confirms the association of SOX1 autoantibodies with SCLC and PNS. The line blot test misses 25% of the cases; therefore, to minimize the frequency of false negative results we recommend the use of a confirmatory test, such as CBA, in patients suspected to have a SCLC-related PNS.

Highlights

SOX1 autoantibodies are serological markers of small cell lung cancer (SCLC).They occur in up to 15% of patients with SCLC independently of the presence of a paraneoplastic neurological syndrome (PNS) [1, 2]
Sera from 210 patients were investigated for the presence of SOX1 autoantibodies by a commercial line blot of recombinant SOX1 and a cell based assay (CBA) of HEK293 cells transfected with SOX1, and the findings were used to calculate the sensitivity and specificity of the commercial line blot test
No clinical differences were noted between these patients and the 18 (25.4%) cases that were SOX1 autoantibody negative by line blot (Table 1)

Summary

Introduction

SOX1 autoantibodies are serological markers of small cell lung cancer (SCLC).They occur in up to 15% of patients with SCLC independently of the presence of a paraneoplastic neurological syndrome (PNS) [1, 2]. The frequency of SOX1 autoantibodies increases to 60% in patients with SCLC and paraneoplastic cerebellar degeneration (PCD) or Lambert-Eaton myasthenic syndrome (LEMS) [3, 4]. SOX1 was first identified as the antigen recognized by anti-glial nuclear antibodies (AGNA) which were characterized by immunohistochemistry showing a characteristic pattern of reactivity with the nuclei of Bergmann glia cells [5]. Unlike other onconeural antibodies, screening by immunohistochemistry is not recommended for the detection of SOX1 autoantibodies because the sensitivity is low compared with that of immunoblot of recombinant SOX1 protein [3]. Recent studies using immunoblot or ELISA suggested that SOX1 autoantibodies can occur in serum of patients with idiopathic polyneuropathies questioning the value of SOX1 autoantibodies as biomarkers of PNS associated with SCLC [9, 10]

Methods

Results

Conclusion