IMPORTANCE OF OVERALL TREATMENT TIME FOR THE OUTCOME OF RADIOTHERAPY OF ADVANCED HEAD AND NECK-CARCINOMA - DEPENDENCY ON TUMOR DIFFERENTIATION

Purpose: Accelerated repopulation of tumor cells during radiotherapy h as been suggested as an important cause of treatment failure in squamo us cell carcinoma of the head ind neck. Due to tumor heterogeneity, no t all tumors may benefit from accelerated radiotherapy at the expense of a lower total dose. This analysis evaluates the impact of histologi cal differentiation on loco-regional control in relation to treatment duration. Patients and methods: A total of 501 patients with advanced supraglottic and pharyngeal squamous cell carcinoma with known histopa thological grading were treated with planned split-course (191 patient s) or continuous radiotherapy (310 patients) in two consecutive random ized controlled trials, irradiation was given 2 Gy per fraction, 5 fra ctions per week to a dose of 66-68 Gy in 9.5 or 6.5 weeks, respectivel y. Results: Overall, split-course and continuous treatment resulted in a 5-year loco-regional control of 30% and 41% (P = 0.007), respective ly. However, the detrimental effects of split-course were only found i n moderately and well-differentiated tumors, where the 5-year tumor co ntrols were 38% and 21% after continuous and split-course treatment, r espectively (P = 0.001). In contrast, in poorly differentiated tumors loco-regional control was obtained in 44% of the cases for continuous and 40% for split-course treatment (P = 0.63). Conclusions: It is sugg ested that the ability to accelerate repopulation may be lost by dedif ferentiation, and that prolongation of the overall treatment time only lead to reduced loco-regional control in well to moderately different iated tumors. (C) 1997 Elsevier Science Ireland Ltd.