5528 Background: CTX constitutes a standard for locoregionally advanced HNC. IndCT may decrease distant failure rates (Brockstein Ann Oncol, 2003). The combination of these approaches has resulted in favorable early survival outcomes. CTX is limited by acute mucositis and long-term functional impairment. We examined the feasibility of lowering radiotherapy doses in sequential groups of patients (pts) to maintain high antitumor activity while decreasing toxicities. Methods: This was a 3-part, nonrandomized, phase II trial. Pts with stage IV (M0) HNC received 8 weeks of IndCT with carboplatin and paclitaxel (groups A & B ); carboplatin, AUC 2, and paclitaxel 135 mg/m2 weekly x 6; group C carboplatin AUC 6 day 1, and paclitaxel 100 mg/m2 days 1, 8, and 15 with cycle 2 beginning day 28. All pts received alternating week CTX with paclitaxel, infusional fluorouracil, oral hydroxyurea, and twice daily radiotherapy (T-FHX) (Kies JCO 2001). Radiotherapy to gross disease, high risk, and low risk microscopic disease consisted of group A (n = 68): 75, 60, 45 Gy; group B (n = 64): 75, 54, 39 Gy; group C (n = 90): 72, 51, 36 Gy. We have previously reported outcome data on groups A & B (Vokes JCO 2002 & Haraf CCR 2003). Results: A total of 222 pts were treated between 11/1998 and 2/2001. 74% were male, median age was 57. Best overall response (groups A/B/C): CR: 83/93/68%. With median follow-up time of 64/53/39 months; 3-year overall survival is 72%/67%/67% (logrank p = 0.76), progression-free survival 72%/65%/59% (logrank p = 0.44), time to progression (TTP, in which deaths prior to progression are censored unless due to treatment-related toxicity) 82%/86%/67% (logrank p = 0.019), and local control92%/97%/86% (logrank p = 0.10). Acute toxicities during concurrent chemoradiotherapy included grade 3/4 mucositis 72/2%; 65/11%; 57/8%; and dermatitis 47/15%; 19/26%; 28/2%. Conclusions: This 3-stage study suggests that acute toxicity can be reduced and high overall survival rates maintained while reducing doses of radiotherapy. The lower 3 year TTP rate in cohort C suggests a dose-response curve in the CTX setting. Schedule B may represent the best therapeutic index. Functional outcomes data are presented separately. [Table: see text]