Despite high radiosensitivity, SCLC is prone to systemic recurrence. Considering the studies on NSCLC, whether further escalation of the RT dose can improve the prognosis of SCLC, requires further study. Many patients with SCLC have concomitant diseases and reduced lung function. Therefore, reducing lung exposure using proton beam therapy (PBT) may be a valid option for high-risk patients. In this issue of the Radiation Oncology Journal, although Seo et al. [4] applied PBT to a group with significantly poorer lung function, oncological outcomes and toxicity profiles were similar to those of the control group. While the literature on PBT for LS-SCLC is limited, this study is valuable in clinical and research terms.

Welsh et al. [5] conducted a phase I/II study, applying chemoradiation and pembrolizumab for LS-SCLC. Grade ≥2 pneumonia occurred in 15%, and median progression-free and overall survival were favorable at 19.75 months and 39.5 months, respectively. Unfortunately, a recent phase II randomized study (STIMULI trial) adding nivolumab and ipilimumab to standard treatment for LS-SCLC failed to demonstrate its benefit, resulting in an increase in grade ≥3 toxicities (62% vs. 25%) [6]. Nonetheless, the efficacy of various immunotherapeutic agents is being evaluated for LS-SCLC [7], hopefully achieving encouraging results as in NSCLC. If potential toxicities can be reduced using PBT, the effectiveness of immunotherapy in treating LS-SCLC may be revealed in the future.

Seo et al [4]. reported the safety and efficacy of PBT in patients with high-risk LS-SCLC. These results may expand the role of RT in high-risk groups of LS-SCLC and help demonstrate the effectiveness of novel agents.