Adding Atezolizumab to Stereotactic Body Radiation Therapy Does Not Improve Survival in Early-Stage Lung Cancer... Monotherapy Recommended
Background
For patients with early-stage Non-Small Cell Lung Cancer (NSCLC) who are unable to undergo surgery due to advanced age or cardiopulmonary disease, Stereotactic Body Radiation Therapy (SBRT), which delivers high-dose radiation focused on the lesion, has become a standard treatment. While local control rates at the tumor site are excellent, reaching around 90%, the suppression of distant metastasis or recurrence remains an area of uncertainty. As the mechanism where radiation triggers a systemic immune response by releasing antigens during the cancer cell death process was revealed, the combination of radiation and immunotherapy has emerged as a major topic in oncology over the past decade. This bolstered the hypothesis that administering Immune Checkpoint Inhibitors (ICI) would extend survival by suppressing potential micrometastases. Researchers from SWOG and NRG Oncology, collaborative groups under the National Cancer Institute (NCI), initiated large-scale clinical trial designs to demonstrate efficacy in real-world patient populations.
Key Findings
The phase 3 randomized clinical trial (SWOG/NRG S1914) published in the international journal The Lancet was conducted on 417 high-risk early-stage NSCLC patients who were inoperable or refused surgery. The research team randomized patients into an SBRT monotherapy group (207 patients) and an SBRT plus atezolizumab group (210 patients). The combination group received 1,200 mg of atezolizumab every 3 weeks for up to 8 cycles, comprising one cycle of neoadjuvant therapy prior to SBRT, concurrent therapy during radiation treatment, and seven cycles of adjuvant therapy post-treatment. The primary endpoint of the study was Overall Survival (OS), with Progression-Free Survival (PFS) and the frequency of adverse events set as key secondary endpoints.
However, the interim analysis results deviated completely from existing expectations. This is because no clinical improvement was observed in either OS or PFS compared to monotherapy, despite the addition of atezolizumab. The 2-year overall survival rate for both groups recorded the same figure of approximately 82%. The risk of disease progression also showed no significant difference between the two treatment groups. The independent data monitoring committee reached a futility conclusion, stating that the possibility of proving treatment efficacy was slim, leading to the early termination of the trial.
In terms of safety indicators, the burden associated with combination therapy was clearly evident. The incidence of Grade 3 or higher severe adverse events remained at the 2-3% level in the SBRT monotherapy group, but soared to 12% in the atezolizumab combination group. With overlapping immune-related side effects, the toxicity risk for patients increased more than fourfold. This provided clinical evidence that the expected systemic anticancer synergy did not materialize, while the frequency of complications increased.
Implications and Outlook
These findings demonstrate that biological mechanisms identified in preclinical stages do not necessarily translate directly into clinical outcomes for patients. It has clarified that SBRT monotherapy remains a well-established standard of care for patients with early-stage NSCLC. Even if immune checkpoint inhibitors have become standard for advanced or metastatic lung cancer, it shows that in early stages with relatively low tumor burden, systemic immune stimulation does not translate into significant survival benefits.
The academic community points out that precise target selection based on biomarkers must precede indiscriminate combination therapy. Rather than applying immunotherapy uniformly to all early-stage patients, the logic is to select a subgroup with a high risk of minimal residual disease by precisely measuring circulating tumor DNA (ctDNA) in the blood or PD-L1 expression levels within tumor tissue. Furthermore, considering the characteristics of the target group, which consists of many elderly patients with comorbid cardiopulmonary diseases, redesigning dosing cycles and durations to minimize treatment toxicity remains a key task for future research.
Radiotherapy and immunotherapy combination has been a field of intense investigation globally over the past decade. The phase 3 randomised clinical trial (SWOG/NRG S1914) in The Lancet by Megan E Daly and colleagues,1 conducted in the USA, evaluated whether adding perioperative atezolizumab (neoadjuvant, concurrent, and adjuvant) to stereotactic body radiation therapy (SBRT) improved outcomes in high-risk, medically inoperable early-stage non-small-cell lung cancer (NSCLC). Its primary objective was to compare overall survival between patients assigned to atezolizumab plus SBRT (n=210) or SBRT alone (n=207).
Clear evidence has been established to support the unwavering recommendation of SBRT monotherapy for early-stage lung cancer patients who are not candidates for surgery, in frontline medical oncology and radiation oncology clinical practice. This result effectively eliminates the risk of patients being exposed to unnecessary immune-mediated pneumonitis or endocrine toxicity by preventing the routine off-label addition of immunotherapy that was previously attempted outside clinical trials. Particularly for elderly patients with chronic obstructive pulmonary disease (COPD) or cardiovascular disease, it provides practical benefits by reducing the risk of hospitalization and treatment discontinuation due to severe complications, while simultaneously alleviating the burden of high out-of-pocket drug costs. Instead of expending resources on early combination therapy, clinicians can adopt a tailored strategy that involves follow-up after radiation therapy and initiates systemic therapy only upon detection of molecular genetic signs of recurrence.