Prognostic value of tumor immune biomarkers in biopsies from patients with refractory solid cancers

PD-L1 and tumor-infiltrating lymphocytes play a key role in the immune escape of cancer, although their prognostic value remains unknown in patients with refractory solid cancer compared to other known prognostic estimation methods. In this ancillary study, we assessed the prognostic value of previously-defined prognostic scores (such as the Royal Marsden Hospital (RMH) score) and of PD-L1, CD3, CD8 and FOXP3 expressions based on immunohistochemistry (IHC) and RNA sequencing (RNAseq) of tumor samples from patients included in the personalized-medicine MOSCATO-02 trial. We collected biopsies with successful IHC analysis from 266 patients treated between April 2016 and September 2017, among whom 170 (63.9%) also had a matched RNAseq. We used a Random Forest model to identify the best prognostic factor, and a Lasso-penalized Cox model to validate the findings. We found that the RMH score was the strongest prognostic factor, with high scores associated with a higher risk of death (Hazard Ratio (HR)=1.29; CI95%[1.19-1.21]). The PD-L1 expression score obtained from IHC analyses was the second-best performing predictor, with the 1+ score (low expression) linked to a lower risk of death (HR=0.564; CI95%[0.539-0.580]). Other tested variables, including primary tumor type and subsequent treatments received following biopsy, were not found significantly linked to prognosis. We found modest correlation between IHC and RNAseq expressions of immune genes, but RNAseq related better to prognosis. Overall, our study supports the use of the RMH score and the assessment of PD-L1 expression in IHC to estimate prognosis in patients with advanced cancer.