Proton-Beam Therapy in Limited-Stage SCLC Shows Promising Efficacy

Proton-beam therapy (PBT) was found to be safe for patients with limited-stage (LS) small-cell lung cancer (SCLC) in the first prospective registry study of the therapy, with only a small number of high-grade toxicities.

“Radiation therapy is essential for the management of limited-stage SCLC,” wrote study authors led by Jean-Claude M. Rwigema, MD, of the Hospital of the University of Pennsylvania in Philadelphia. “When it is given with concurrent chemotherapy, radiation therapy can result in substantial toxicities.” PBT can reduce the exposure to nearby organs at risk in non–small-cell lung cancer, and is under substantial investigation in that setting; before the new study, though, only a six-patient case series had examined its use in SCLC.

The trial included 30 consecutive patients with limited-stage SCLC, treated with a median PBT dose of 63.9 cobalt gray equivalents. Most patients received concurrent cisplatin/etoposide chemotherapy (70%), and some received carboplatin/etoposide (30%). Patients had a median age at diagnosis of 68 years, most were female (70%), and most were white (86.7%). The results of the study were published online ahead of print in Cancer.

Among 27 patients evaluable for initial treatment response, 11 (40.7%) experienced a complete response; another 15 patients (55.6%) had a partial response, and one patient (3.7%) had stable disease. The 1-year local control rate was 85%, and the 2-year rate was 68.6%; the median recurrence-free survival duration was 14.3 months. The median overall survival in the study was 28.2 months, and the 1- and 2-year overall survival rates were 71.5% and 57.6%, respectively.

For comparison, the researchers generated clinical backup intensity-modulated radiotherapy (IMRT) plans for each patient. PBT resulted in significantly reduced doses to the spinal cord (P = .004), lung (P = .002), and heart (P < .001), but not to the esophagus (P = .22), compared with IMRT.

PBT was generally well tolerated in the study. Grade 2 or higher pneumonitis occurred in 13.3% of patients, after a median of 5.2 months from treatment initiation; only one such case was a grade 3 event. Grade 2 esophagitis occurred in 43.3% of patients. One patient treated with twice daily PBT experienced grade 3 pericardial effusion, and one other experienced grade 4 esophagitis; a case of grade 3 anorexia was the only other grade 3 or higher non-hematologic toxicity.

“PBT as part of a combined modality therapy for LS-SCLC is feasible and safe, with preliminary evidence showing encouraging efficacy in comparison with photon radiation,” the authors concluded. “Additional comparative studies of PBT and photon therapy in LS-SCLC appear warranted.”