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MINI 38 - Biology and Prognosis (ID 167)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Thymoma, Mesothelioma and Other Thoracic Malignancies
- Presentations: 1
MINI38.12 - Multiplex Immunofluorescence Identifies Differences in Immune Microenvironment & Prognostic Biomarkers between Mesothelioma Subtypes (ID 3217)
18:30 - 20:00 | Author(s): S. McGregor
Malignant mesothelioma (MM) is a universally lethal disease, which develops in the pleura, peritoneum, pericardium, and tunica vaginalis. MM is commonly associated with a prominent inflammatory reaction, including extensive macrophage infiltration. Early reports indicate presence of tumor infiltrating lymphocytes (TILs), PD-L1 expression (Kindler et al ASCO 2014), and activity of anti-PD-1 therapy (Alley et al AACR 2015). However, quantitative evaluation of multiple immune markers in a large mesothelioma cohort and evaluation of prognostic and biologic implications has not been reported.
We performed multiplex immunofluorescence (IF) staining and automated, quantitative density assessments in a clinically annotated cohort of 109 malignant mesotheliomas (58 epithelioid, 43 biphasic, 8 sarcomatoid). Staining for PD-1, PD-L1 (immune checkpoint), FOXP3 (T-regulatory cells), and CD8 (TILs) was performed using a quantitative, multiplex IF system (TissueFax), and a multi-tumor-validated, quantitative StrataQuest analysis algorithm in order to identify specific immune cells and respective densities. Gene expression data (TCGA) was analyzed to confirm individual correlations. Staining for CD206 (macrophages) is ongoing.
PD-L1 density correlated with more aggressive histology, and was highest in sarcomatoid (median density score of 3016), and biphasic (2720) tumors compared with epithelioid tumors (1740). Using a cutoff of 5% PD-L1 density by area 19% of epithelioid, 38% of sarcomatoid, and 44% of biphasic tumors were deemed PD-L1 positive. PD-L1 expression exhibited a bimodal distribution (peaks at both high and low PD-L1 densities). Also with the biphasic tumor cohort expression of PD-L1 correlated with worse outcome (P=0.02), while PD-1 and CD8 did not have prognostic implications (and could not distinguish histologic subtypes). By contrast in epithelioid MM CD8 infiltration density showed a trend towards improved prognosis (P=0.06) (and correlated with PD-1 expression), while PD-L1 expression was not prognostic. Interestingly, PD-1/CD8 and PD-L1 expression did not correlate regardless of histology (R=0.02-0.08), suggesting macrophage-driven PD-L1 expression. Gene expression data supported this hypothesis and staining for M2-related macrophage markers is ongoing. In epithelioid tumors FOXP3 T-regulatory cell density showed a trend towards worse prognosis (P=0.07). In biphasic and sarcomatoid tumors prognosis was poor regardless of FOXP3 expression. Data on stromal versus tumor expression patterns is being processed.
In mesothelioma CD8, PD-1, PD-L1 and FOXP3 are widely expressed, with 19% of epithelioid, and 38-44% of sarcomatoid and biphasic tumors showing elevated PD-L1 density. PD-L1 expression correlates with a worse prognosis by subtype and in the biphasic tumor population. In epithelioid tumors PD-1 may indicate better outcome. PD-1 and PD-L1 expression do not correlate with each other in malignant mesothelioma, which relates to pro-tumorigenic macrophages leading to potentially interferon gamma independent PD-L1 expression.
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