Prognostic Factors in Limited-Stage Small Cell Lung Cancer: A Secondary Analysis of CALGB 30610-RTOG 0538.

IMPORTANCE

The impact of patient-specific, disease-related, and social factors on outcomes in limited-stage small cell lung cancer (LS-SCLC) is not well defined. A post hoc secondary analysis of such factors from the Cancer and Leukemia Group B (CALGB) 30610-Radiation Therapy Oncology Group (RTOG) 0538 trial may impact future trial design.

OBJECTIVE

To assess the comprehensive demographic, disease-related, treatment-related, and social factors for potential associations with survival outcomes and understand whether specific subpopulations may benefit from radiotherapy (RT) dose escalation in LS-SCLC.

DESIGN, SETTING, AND PARTICIPANTS: This post hoc secondary analysis of a randomized clinical trial included 638 adults with LS-SCLC treated at 186 unique treatment sites with at least 1 accrual for all patients from March 15, 2008, to December 1, 2019; 313 patients were randomized to receive RT twice daily to a dosage of 45 Gy for 3 weeks and 325 to receive RT once daily to a dosage of 70 Gy for 7 weeks. Data were locked February 28, 2022, and analyzed from November 28, 2022, to June 4, 2024.

INTERVENTIONS

Twice-daily RT or once-daily RT.

MAIN OUTCOMES AND MEASURES

Multivariable Cox proportional hazards models evaluated the association of treatment groups and other risk factors with progression-free survival (PFS) and overall survival (OS). Patient-specific factors included age, sex, and Eastern Cooperative Oncology Group performance status. Disease-related factors included tumor, nodal, and overall cancer stages. Treatment-related factors included type of chemotherapy, timing of concurrent RT, RT technique, and prophylactic cranial irradiation. Social factors included marital status and treatment center accrual volume.

RESULTS

Among 507 patients (260 [51.3%] female and 247 [48.7%] male; mean [SD] age, 62.6 [7.9] years) included in the multivariate survival analysis, with a median follow-up of 4.7 (IQR, 3.7-7.1) years, female sex was associated with improved OS (hazard ratio [HR], 0.73 [95% CI, 0.58-0.91]; P = .006), while being 70 years or older was associated with decreased OS (HR, 1.50 [95% CI, 1.14-1.98]; P = .004). Neither age nor sex was associated with PFS. When compared with those with N1 disease, OS and PFS were worse in patients with N2 (HRs, 1.64 [95% CI, 1.19-2.26]; P = .002 and 1.36 [95% CI, 1.02-1.81]; P = .04, respectively) and N3 (HRs, 2.03 [95% CI, 1.40-2.93]; P < .001 and 1.63 [95% CI, 1.17-2.26]; P = .004) disease. Compared with stage II cancer, OS was worse for stage IIIA (HR, 1.65 [95% CI, 1.17-2.31]; P = .004) and stage IIIB (HR, 1.94 [95% CI, 1.34-2.83]; P < .001). Compared with high-volume accrual centers, treatment at low- or middle-volume accrual centers was associated with worse PFS (HRs, 1.94 [95% CI, 1.33-2.82; P < .001] and 1.44 [95% CI, 1.15-1.82; P = .002], respectively) and worse OS (HRs, 1.55 [95% CI, 1.03-2.32; P = .03] and 1.33 [95% CI, 1.04-1.70; P = .02], respectively).

CONCLUSIONS AND RELEVANCE

This secondary analysis of the CALGB 30610-RTOG 0538 randomized clinical trial of patients with LS-SCLC found associations between female sex or being younger than 70 years and improved overall survival and between advanced nodal stage or treatment at low- or middle-volume accrual centers and worse outcomes. These findings suggest that stratification by nodal stage, clinical stage, and age should be considered in future randomized trials.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00632853.