Stereotactic ablative radiation therapy versus conventionally fractionated radiation therapy for stage I small cell lung cancer

Background: The National Comprehensive Cancer Network (NCCN) recently revised recommendations for inoperable stage I small cell lung cancer (SCLC), having added stereotactic ablative radiotherapy (SABR)/chemotherapy to the historical paradigm of concurrent conventionally-fractionated radiation therapy (CFRT)/chemotherapy. Despite the conformality, convenience, and cost-effectiveness of SABR, the NCCN continues to recommend both CFRT/chemotherapy and SABR/chemotherapy primarily because these approaches have not been comparatively analyzed to date.

Methods: The National Cancer Database was queried for histologically-confirmed T1-2N0M0 SCLC; all patients received chemotherapy. Multivariable logistic regression ascertained factors associated with SABR/chemotherapy. Kaplan-Meier analysis assessed overall survival (OS); multivariable Cox proportional hazards modeling examined factors associated with OS. Survival was also calculated following propensity matching.

Results: Of 2,107 patients, 7.1% underwent SABR/chemotherapy, and 92.9% received CFRT/chemotherapy. The median (interquartile range) dose of SABR was 50 (48-54) Gy in 4 (3-5) fractions, and 55.8 (45-60) Gy in 30 (30-33) fractions for CFRT. Patients receiving SABR/chemotherapy were more often older, had T1 disease, treated at academic/integrated network facilities, and managed in more recent years (p < 0.05 for all). Respective median survival figures were 29.2 versus 31.2 months (p = 0.77), which persisted following propensity matching (25.4 versus 34.3 months, p = 0.85). On multivariable analysis, radiotherapeutic technique was not associated with OS (p = 0.95).

Conclusions: For stage I SCLC, SABR/chemotherapy affords statistically equivalent outcomes to CFRT/chemotherapy. Because randomized studies addressing this uncommon scenario would almost certainly suffer from inadequate accrual, these retrospective data should be strongly considered in efforts to institute SABR/chemotherapy as the preferred option for this population.