Do Tumor PD-L1 Expression and Neutrophil to Lymphocyte Ratio Influence the Efficacy of Stereotactic Radiosurgery for Brain Metastases from Non-Small Cell Lung Cancer?

Abstract

The immune system plays an important role in the pathogenesis and treatment of non-small cell lung cancer (NSCLC). In this study, we explore if immune parameters influence the presentation of limited brain metastases or the efficacy of stereotactic radiosurgery (SRS) for brain metastases from non-small cell lung cancer (NSCLC). We identified patients with NSCLC who were treated with SRS for brain metastases for NSCLC at our institution, underwent post-treatment brain MRI, and had immunohistochemical tumor PD-L1 testing between 2016 and 2017. Responses were quantified using percent change in tumor diameter. Pearson correlation coefficients were used to assess for associations between immune parameters (PD-L1 tumor proportion score and neutrophil-to-lymphocyte ratio[NLR]) and clinical findings. Logarithmic or square root transformations were applied as needed to facilitate parametric testing. Twenty-four patients who underwent 32 courses of stereotactic radiosurgery met eligibility criteria. Median tumor size before treatment was 0.9 cm (range: 0.2 to 3.4 cm). Thirty treatments were delivered in a single fraction (18-24 Gy), and two were delivered in 5 fractions (30-32.5 Gy). Median PD-L1 expression was 10%, and eight patients had high (≥50%) PD-L1 expression. Median NLR before corticosteroid initiation was 3.3. Immunotherapy was delivered prior to SRS in 9 cases. In 8 of those cases, immunotherapy was continued after SRS. In 2 cases immunotherapy was initiated after SRS and before follow-up MRI. One patient who received immunotherapy experienced mild blurry vision, but otherwise no toxicities were noted in the 30 days following SRS. Mean percent change in tumor diameter following SRS was -32% (range: -100% to +140%). PD-L1 expression was inversely associated with metastasis size (p=0.091). Median diameter was 1.3 cm for patients with PD-L1 expression below 10%, compared with 0.7 cm for patients with PD-L1 of at least 10%. NLR was positively associated with metastasis size (p=0.081). PD-L1 expression, NLR, and receipt of immunotherapy before or after SRS were not associated with response to SRS. Tumor and patient immune parameters may influence the presentation of limited brain metastases in NSCLC patients. We did not find that immune parameters or administration of immunotherapy influence radiographic response rates following SRS. Additional studies are required to determine if local management of brain metastases should be altered with the growing role of immunotherapy in the treatment of NSCLC. Moreover, immunotherapy delivered in conjunction with stereotactic radiosurgery appeared to be well tolerated.