Relationship between tumour cell in vitro radiosensitivity and clinical outcome after curative radiotherapy for squamous cell carcinoma of the head and neck

Background and purpose: Clinically, it is recognized that individual tumour s respond differently to radiation treatment. Variation in tumour cell radi osensitivity is believed to be an important underlying factor. In the curre nt study, cellular in vitro radiosensitivity was estimated as the fraction of surviving cells after a radiation dose of 2 Gy (SF2) and related to clin ical outcome after curative radiotherapy. Patients and methods: Thirty-eight patients with squamous cell carcinoma of the head and neck were treated with curative radiotherapy alone. Pre-treat ment biopsies were disaggregated to form a single-cell suspension and cells were cultured in the modified Courtenay-Mills soft agar clonogenic assay. Directly from this assay and with no respect to cell type, overall SF2 was assessed. By collecting the obtained colonies on a preparation slide using a colony-filter technique, and with immunocytochemical staining, it was pos sible to measure the surviving fraction of tumour cells selectively as tumo ur cell SF2. Results: Experimentally, a broad inter-tumour variation was found for both tumour cell SF2 and overall SF2. Using weighted linear regression, it was d emonstrated that tumour cell SF2 and overall SF2 were two independent measu res of tumour radiosensitivity. In general, the measures of tumour radiosen sitivity were independent of patient sex and age, T- and N-category, diseas e stage, tumour size and plating efficiency. Among the 38 patients grouped in loco-regional failures and patients with loco-regional control, respecti vely, sex, age, total radiation dose, overall treatment time and tumour gra de were equally distributed. Advanced stage, lymph node involvement and tum our size correlated statistically significantly with poor loco-regional con trol. Neither tumour cell SF2, overall SF2, nor plating efficiency predicte d loco-regional tumour control probability. In a multivariate analysis with respect to the risk of loco-regional tumour failure, only disease stage yi elded independent prognostic significance. This significance suggests that this patient sample was representative for the patient population with head and neck cancer. Conclusion: In 38 patients with squamous cell carcinoma of the head and nec k, the estimated tumour radiosensitivities were not statistically related t o clinical outcome after curative radiotherapy alone. (C) 1999 Elsevier Sci ence Ireland Ltd. All rights reserved.