Materials and Methods
Patient selection
In this retrospective cohort study, we reviewed the cases of 167
patients from five centers in Bulgaria with metastatic NSCLC treated
with pembrolizumab after progression upon first-line platinum-based
chemotherapy between April 2017 and February 2020. The procedure was
approved by the Scientific Research Ethics Committee at the Hospital
“Nadezhda” in Sofia. The eligibility criteria were as follows: (1) age
≥18 years old, (2) histologically confirmed diagnosis of NSCLC in the
metastatic stage, (3) wild-type epidermal growth factor
receptor/anaplastic lymphoma kinase, (4) Eastern Cooperative Oncology
Group-Performance status (ECOG-PS) < 2, (5) disease
progression after receiving one prior platinum-based systemic therapy
for metastatic disease with measurable disease lesions, (6) available
blood cell count and blood samples, and (7) available computed
tomography (CT) scans. Immunotherapy were administered after at least 3
weeks after previous treatment. Patients were excluded if they had brain
metastases (since corticosteroid use may compromise therapy), autoimmune
disease, symptomatic interstitial lung disease, systemic
immunosuppression, or prior treatment with immune-stimulatory antitumor
agents, including checkpoint inhibitors. Patients did not show any
clinical or computed tomography signs of active infection. Tumor PD-L1
status was assessed. Pembrolizumab was initially administered via 2
mg/kg intravenous (i.v.) injection over 60 minutes every 3 weeks and
later via 200 mg i.v. injection (flat dose) every 3 weeks.