Data collection
Data collected included demographics, PD-L1 status, metastatic sites, description of first-line treatment, date of progression as determined by radiology reports, and date of death or last follow-up. Peripheral blood samples were collected from patients included in the study the day of first-line chemotherapy administration at baseline and the day of first immunotherapy infusion upon progression. Of interest were the following hematological and biochemistry parameters: absolute neutrophil count (ANC), absolute lymphocyte count (ALC) and platelet count (APC), which enable calculation of the NLR (neutrophil to lymphocyte ratio: ANC/ALC) and the PLR (platelet to lymphocyte ratio: APC/ALC). NLR1 and PLR1 were calculated before the first cycle of chemotherapy, and NLR2 and PLR2 were calculated before the first pembrolizumab infusion. ΔNLR (NLR2-NLR1) and ΔPLR (PLR2-PLR1) were calculated. An NLR>5 was considered high in accordance with earlier reports [19-21]. The median value of NLR2 was 4.8. The median value (174) of the PLR was used to group cases into two categories of low (≤median) and high (>median) PLRs.
The tumor PD-L1 protein expression was analyzed by immunohistochemistry of tumor cells in archived biopsy samples of tumors, and the cutoff for positivity was 1%. In addition, we subdivided the positive group into expression categories: expression in 50%, expression in 25-49%, and expression in 1-24%.