For a study, researchers sought to study that concurrent chemoradiotherapy  (CCRT) is the gold standard of treatment for persons with recently discovered limited-stage small-cell lung cancer (SCLC). Even if an early response was attained, the prognosis was still poor due to SCLC’s aggressiveness and high likelihood of recurrence or relapse. As a result, there was a critical therapeutic need for this population. Therefore, patients with previously untreated limited-stage SCLC participated in the multicenter, phase 3, randomized, placebo-controlled, double-blind KEYLYNK-013 research (NCT04624204), which assessed the effects of adding pembrolizumab to CCRT followed by pembrolizumab with or without olaparib. CCRT (etoposide with carboplatin or cisplatin for 4 cycles and conventional thoracic irradiation) with pembrolizumab (Groups A and B) or CCRT plus placebo will be administered to eligible volunteers aged more or around 18 with newly diagnosed, pathologically proven, limited-stage (i.e., stage I-III) SCLC (Group C). Participants will either get a placebo, pembrolizumab plus olaparib, or pembrolizumab plus olaparib in the absence of disease progression (Group C). According to RECIST version 1.1, the 2 primary goals were overall survival and progression-free survival, which were selected by a blinded independent central review. At more than 150 locations, enrollment started in December 2020 and is still going strong. Important details on the effectiveness and safety of pembrolizumab plus CCRT and pembrolizumab with or without olaparib post-CCRT in patients with limited-stage SCLC will be revealed by KEYLYNK-013.