The results of this study, based on dynamic monitoring of CSF IL-10 concentrations, are consistent with those of previous studies demonstrating IL-10 as a biomarker of PCNSL. Most importantly, for the first time, we demonstrated that CSF IL-10 changes display better performance in predicting disease relapse than conventional MRI.
Because patients with PCNSL commonly present with nonspecific neurologic symptoms, the diagnostic process may be delayed for months to years. Since 2012, several studies have evaluated the diagnostic value of CSF IL-10 concentration or the ratio of IL-10/IL-6[11, 12, 19]. Although IL-10 has been identified as a specific biomarker for PCNSL, its origin remains uncertain. Rubenstein et al. demonstrated IL-10 overexpression in lymphoma cells by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry analysis, while Sasayama confirmed the expression of IL-10 in CD68 + and CD163 + tumor-associated macrophages (TAMs) by double immunostaining analysis[11, 20]. Soussain reported a trend of lower IL-10 levels after corticosteroid treatment[16]. We also observed a rapid decrease IL-10 in levels several days after corticosteroid administration in our clinical practice; while IL-10 levels may sometimes decrease to the normal range, no change in the tumor is observed on computed tomography (CT) scan. This mismatch between CSF IL-10 decrease and CT scan findings hints that CSF IL -10 is not generated exclusively by tumor cells.
Based on our previous findings, we extended the cohort and performed dynamic surveillance of CSF IL-10 concentrations. Our data are consistent with those of previous studies showing elevated CSF IL-10 concentrations in PCNSL. There is a trend toward decreased sensitivity and specificity of CSF IL-10 when more PCNSL patients were enrolled, and a similar result was observed in our center. Song et al reported that the diagnostic sensitivity of 95.5% for CSF IL-10 concentration > 8.2 pg/mL in 22 PCNSL patients[12] decreased to 85% when the cohort was expanded to 40 patients. Meanwhile, the positivity rate in relapsed patients 78.9% (19/24), much lower than that in newly diagnosed patients. However, studies differ in IL-10 measurement methods and patient selection; furthermore, many factors can influence CSF IL-10 concentration, including corticosteroid use, disease status, and PCNSL subtype.
We explored new perspectives of CSF IL-10 in the subgroups. Pretreatment IL-10 concentration was associated with tumor burden, as the CSF cytology-positive and multi-lesion subgroups showed higher IL-10 levels. While the prognostic impact on outcome of CSF IL-10 concentration has been widely evaluated in previous studies, the results are controversial. Sasayama et al. reported that high pretreatment IL-10 levels were related to poor PFS, although the cutoff values were different. Nguyen-Them et. al did not observe a negative impact of pretreatment IL-10 level on PFS in a larger cohort and reported that persistent detectable CSF IL-10 at the end of treatment was a negative factor of PFS. The present study obtained results similar to those reported by Nguyen-Them et al in which only persistent detectable CSF IL-10 at end-induction was associated with poor PFS. The role of prognosis based on CSF IL-10 level requires evaluation in future studies with larger populations, a uniform method, and combined with other potential biomarkers of PCNSL.
The most impressive finding of the present study was that CSF IL-10 relapse was an earlier surrogate biomarker for disease relapsing, a result that, to our knowledge, has not been reported previously. Late relapse is common in PCNSL and more than 25% of patients relapse after 2 years. There remain no accurate factors to predict relapse. Song et al and Nguyen-Them et al reported the relationship between increased CSF IL-10 concentration and disease relapse/progression in occasional cases[12, 16]. We performed sequential monitoring by MRI and lumbar puncture in most patients. The data confirmed increased CSF IL-10 concentrations in patients with relapse. We observed that IL-10 relapse occurred a median of 67 days earlier than clinical and/or radiology relapse in 62.5% (10/16) of patients with relapse. This is an encouraging discovery, suggesting that CSF IL-10 is a potential candidate as a predictor of relapse. CSF IL-10 relapse is likely related to micro-lesions in the CNS that cannot be detected by MRI. In 2019, Grommes et al. evaluated the effects of CSF circulating-tumor DNA (ctDNA) and MRI on relapse in surveillance of nine patients with r/rCNSLs treated with ibrutinib plus high-dose methotrexate (MTX). ctDNA was analyzed using MSK-HemPACT, a custom FDA-authorized next-generation sequencing-based tumor sequencing assay. Only one of nine patients showed ctDNA relapse before MRI relapse and no superiority was found for ctDNA analysis compared to MRI monitoring. CSF IL-10 had a higher sensitivity than conventional MRI scans and novel NGS technology. While CSF IL-10 relapse is not definitive evidence of relapse, this discovery provides a new perspective for PCNSL follow-up. CSF IL-10 concentration can be used as a tool for minimal residual disease (MRD). The combination of CSF biomarkers and image surveillance can provide more accurate information on PCNSL relapse. CSF IL-10 monitoring by lumbar puncture is an invasive procedure that limits its use but that can be used to predict disease relapse.
The limitations in this study include the biases inherent to retrospective studies, the limited scale of the cohort, the heterogeneity of therapy regimens, and the lack of follow-up data. The higher proportion of patients with PVRL enrolled in this study may have affected the interpretation of the results. Six (10%) patients had PVRL subtype, five of whom showed sustained CSF IL-10 level at CR. Finally, lumbar puncture is an invasive procedure that is widely used in routine practice.
In conclusion, this study adds strong evidence to previous studies on the utility of CSF IL-10 levels in PCNSL diagnosis and prognosis. We defined IL-10 relapse and showed the correlation between IL-10 and disease relapse for the first time. CSF IL-10 showed relapse a median of 2-months earlier than MRI showed relapse in most patients, suggesting CSF IL-10 as a potential surrogate biomarker for PCNSL relapse. More research is needed to clarify the origin and impact of IL-10 in PCNSL pathogenesis. The potential role of IL-10 as a surrogate marker for relapse and therapeutic response in PCNSL should also be validated in an independent series along with other potential biomarkers.