In vitro parameters and treatment outcome in head and neck cancers treated with surgery and/or radiation: Cell characterization and correlations with local control and overall survival

Abstract

Purpose: To determine whether in vitro parameters (surviving fraction at 2 Gy, alpha values, and calculated cell growth fraction) were predictive of the treatment outcome. Methods and Materials: Biopsies were obtained from patients with a head and neck tumor. In vitro parameters were determined using the CAM plate assay. Cell characterization by cytogenetic analysis was performed on 19 different cell cultures. In 25 additional cell cultures, cell clonogenicity was tested using the Courtenay Mills assay. Results: Biopsies were obtained from 156 patients with a head and neck tumor and the oropharynx was the predominant primary site. In vitro parameters were obtained in 113 cases (72%) (SF2 in 93 cases and calculated cell growth fraction in 103 cases). Cell characterization showed that cells in CAM plates were diploid with no clonal chromosome abnormalities and gave colonies in soft agar with a mean cloning efficiency of 1.610 −3. Only patients treated with surgery and/or radiation (76), were considered eligible for in vitro parameters and treatment outcome correlation studies. The mean follow-up is over 2 years (range 9–47 months). The local control rate was significantly higher ( p = 0.04) for patients with alpha values above the cut-off point of 0.07 Gy −1 (69% vs. 38% at 2 years). The local control rate was also significantly higher ( p = 0.04) for patients with calculated cell growth fraction values above the cut-off point of 0.06% (70% vs. 48% at 2 years). Moreover for these latter patients the overall survival rate was also significantly higher ( p = 0.004) (54% vs. 26% at 2 years). It is worth noting that alpha and calculated cell growth fraction values below the cut-off points identified a small group of patients (about 20%) who were at a significantly high risk of local failure. From a pragmatic point of view, as only radiosensitivity or calculated cell growth fraction values could be obtained in a certain number of experiments due to technical reasons, the treatment outcome of patients who had either alpha and/or calculated cell growth fraction values below the cut-off levels (about 30% of all patients) was analyzed. This group of patients fared significantly worse ( p = 0.02) in terms of local control (50% vs. 68% at 2 years) and ( p = 0.04) overall survival (36% vs. 50% at 2 years). Conclusion: These results suggest that in vitro parameters using the CAM plate assay, might be useful in predicting the treatment outcome of patients with a head and neck tumor treated with surgery and postoperative radiation, or radiation alone. However, they must be considered as preliminary because the cut offs used in the study were chosen for exploratory purposes. Only a multivariate analysis including all clinical and biologic factors will allow us to draw any firm conclusions.