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Despite the advances in radiation techniques and chemotherapy, survival with current platinum-based chemotherapy and concomitant thoracic radiation remains dismal. Bortezomib, a proteasome inhibitor, modulates apoptosis and cell cycle through disruption of protein degradation. The combination of bortezomib and carboplatin/paclitaxel and concurrent radiation in unresectable stage III non–small-cell lung cancer was evaluated in this phase I/II study.Patients with histologic or cytologic confirmed stage III nonmetastatic non–small-cell lung cancer who were candidates for radiation therapy were eligible. In the phase I portion, patients received escalating doses of bortezomib, paclitaxel, and carboplatin concomitantly with thoracic radiation (60 Gy/30 daily fractions) using a modified 3 + 3 design. The primary endpoint for the phase II portion was the 12-month survival rate (12MS). A one-stage design with an interim analysis yielded 81% power to detect a true 12MS of 75%, with a 0.09 level of significance if the true 12MS was 60% using a sample size of 60 patients. Secondary endpoints consisted of adverse events (AEs), overall survival, progression-free survival, and the confirmed response rate.Thirty-one patients enrolled during the phase I portion of the trial, of which four cancelled before receiving treatment, leaving 27 evaluable patients. Of these 27 patients, two dose-limiting toxicities were observed, one (grade 3 pneumonitis) at dose level 1 (bortezomib at 0.5 mg/m2, paclitaxel at 150 mg/m2, and carboplatin at area under the curve of 5) and one (grade 4 neutropenia lasting ≥8 days) at dose level 6 (bortezomib 1.2 mg/m2, paclitaxel 175 mg/m2, and carboplatin at area under the curve of 6). During the phase I portion, the most common grade 3 of 4 AEs were leukopenia (44%), neutropenia (37%), dyspnea (22%), and dysphagia (11%). Dose level 6 was declared to be the recommended phase II dose (RP2D) and the phase II portion of the study opened. After the first 26 evaluable patients were enrolled to the RP2D, a per protocol interim analysis occurred. Of these 26 patients, 23 (88%) survived at least 6 months (95% confidence interval [CI], 70–98%), which was enough to continue to full accrual per study design. However, due to slow accrual, the study was stopped after 27 evaluable patients were enrolled (6—phase I RP2D; 21—phase II). Of these 27 patients, the 12MS was 73% (95% CI, 58–92%), the median overall survival was 25.0 months (95% CI, 15.6–35.8), and the median progression-free survival was 8.4 months (95% CI, 4.1–10.5). The confirmed response rate was 26% (seven of 27; 95% CI, 11–46%), consisting of four partial responses and three complete responses. Grade 3+ and grade 4+ AEs occurred in 82% and 56% of patients, respectively. One patient experienced grade 5 pneumonitis that was possibly related to the treatment. Grade 3 and 4 hematological toxicities were observed in 82% and 56% patients, respectively.The addition of bortezomib to concurrent carboplatin/paclitaxel and radiation seemed to be feasible, although associated with increased hematological toxicities. A favorable median overall survival of 25 months suggests a potential benefit for this regimen.