Cancer is still a big threat to the global healthcare system, notwithstanding the progress of various treatment methods. Traditional therapies including chemotherapy and radiotherapy are generally not specific and bring with them significant side effects. The personalized medicine approach, which is based on the individual's molecular and genetic profiles, is an upcoming strategy that offers the promise of more effective and safer cancer treatment. In the world of oncology precision medicine has brought about personalized methods, especially in cancer immunotherapy. This research aimed the efficacy of pembrolizumab treatment in patients with NSCLC in advanced stage as a singular therapy. The subjects of the study were 150 patients with an overall median age of 62, most of them male, with adenocarcinoma as their main histology, and stage IV as their primary trait. Objects with 35% response rate and 50% disease control rate have been treated with pembrolizumab. The progression-free survival was 8.5 months and overall survival was 18.9 months for the median. By and large, these adverse events were bearable, with the symptoms such as fatigue, diarrhoea and pruritus being the most common. This data points to the vital role of individualized immunotherapy in the treatment of NSCLC, showing that the use of pembrolizumab monotherapy is a valid option for patients with advanced disease. Additional studies are needed to maximize treatment protocols and develop diagnostic biomarkers to facilitate early detection and better patient outcomes.