Introduction: Clinical and laboratory parameters associated with response for patients with advanced pre-treated malignant pleural mesothelioma (MPM) are lacking. We aimed to identify prognostic and predictive markers among patients with relapsed MPM who were randomised into the ETOP 9-15 PROMISE-meso phase III trial, evaluating pembrolizumab and chemotherapy.

Methods: Baseline clinical and laboratory parameters were investigated for prognostic or predictive value on progression-free survival (PFS) and overall survival (OS) in a retrospective analysis, based on the full cohort of 144 MPM patients. These consisted of immune-inflammatory indexes (neutrophil-lymphocyte ratio [NLR], systemic immune-inflammatory index [SII], lactate dehydrogenase [LDH]) along with other already known prognostic baseline characteristics and laboratory values. Cut-offs were chosen independently of outcome. Based on Cox multivariable analysis for PFS in the whole cohort, a risk factor model was built to illustrate the prognostic stratification of patients by the combination of the derived independent prognostic factors, taking into account the EORTC score, a validated prognostic score in MPM. All models were stratified by histology and adjusted by treatment.

Results: In the stratified multivariable analysis in the whole cohort, high SII (hazard ratio (HR) 2.06; 95%CI 1.39-3.05) and low haemoglobin (HR 1.62; 95%CI 1.06-2.50) were associated with worse PFS. Based on these two prognostic factors, a mesothelioma risk score (MRS) was constructed with three PFS risk prognosis categories: favourable, intermediate and poor with 0, 1 and 2 risk factors, respectively (corresponding percent of cohort: 24%, 34% and 42% and median PFS: 5.8, 4.2 and 2.1 months). The derived MRS stratified the prognosis for PFS and OS, overall and within each of the EORTC groups. No significant predictors of treatment benefit were identified.

Conclusions: The proposed MRS is prognostic of patient outcome and it fine-tunes the prognosis of patients with pre-treated MPM alone or when used with the already established EORTC score.