PURPOSE: A Phase I/II clinical study using pulsed low-dose paclitaxel and radiation for thoracic malignancy was conducted. The study was based on preclinical research of the effects of paclitaxel on apoptosis and the cell cycle in human cancer cell lines. EXPERIMENTAL DESIGN: Three human epithelial cancer cell lines were investigated for preclinical study. Cells were analyzed for apoptosis and cell cycle characteristics after paclitaxel treatment. The Phase I/II clinical trial for non-small cell lung cancer used pulsed low-dose paclitaxel three times/week with the starting dose of 15 mg/m(2). Daily thoracic radiotherapy was delivered in 1.8 Gy/fraction to 60-65 Gy for gross disease and to 45-58 Gy for microscopic disease. Timing of radiotherapy was delayed to allow for a minimum of 4 h for cell cycle progression. RESULTS: Forty-one patients have enrolled and 33 completed treatments. Seventeen patients completed the Phase I study, with an average primary tumor shrinkage of 83 +/- 8% (95% confidence interval). Tumor response rate was 100% for the Phase I study. Overall local control was 98%, and the survival rate was 46% at 1 year, 33% at 2 years, and 18% at 3 years. Toxicity was low with 3 of 18 patients having grade 3 pneumonitis and 3 of 18 patients having grade 3 esophagitis. There was no grade 4 pneumonitis, esophagitis, or hematological toxicity. CONCLUSIONS: Pulsed low-dose paclitaxel radiosensitization for non-small cell lung cancer resulted in a superior local control rate and comparable survival rate when compared with chemoradiation regimens using systemic dose chemotherapy. The regimen is associated with low toxicity and deserves additional investigation, particularly in patients with poor performance or older age, who cannot tolerate standard chemoradiation regimens.