Transforming growth factor-α: a surrogate endpoint biomarker?

BACKGROUND: Dysplastic oral leukoplakia (DOL) has been the index lesion in prevention trials for upper aerodigestive tract squamous cell carcinoma (SCC). Vitamin A derivatives, including 13-cis retinoic acid (13-CRA), have been used to treat DOL and to reduce the risk of subsequent SCC. Results from a trial of 13-CRA in patients with DOL are presented here. Transforming growth factor-α (TGF-α) and the epidermal growth factor receptor messenger RNA (mRNA) expression were studied to validate their use as surrogate endpoint biomarkers in prevention trials for SCC. STUDY DESIGN: In a prospective, randomized, double-blind trial of 13-CRA in 28 patients with DOL, TGF-α and epidermal growth factor receptor mRNA expression were analyzed in sequential biopsy specimens of DOL and of adjacent normal-appearing mucosa, utilizing a quantitative, competitive, reverse transcriptase polymerase chain reaction and were compared using the Wilcoxon signed-rank test for paired comparisons. RESULTS: In biopsy specimens of DOL, TGF-α mRNA expression at baseline, but not baseline expression of epidermal growth factor receptor mRNA, was significantly elevated when compared with its expression in specimens from adjacent normal-appearing mucosa (p = 0.003). In patients randomized to 13-CRA who had ≥ 50% clearance of DOL during treatment, significant modulation of TGF-α mRNA overexpression was seen after 6 months of treatment (p = 0.016). TGF-α mRNA overexpression at baseline predicted a subsequent response to 13-CRA (p = 0.066). CONCLUSIONS: The full extent of the association between TGF-α overexpression and the development of SCC is unknown. Evidence is presented in this article that TGF-α overexpression mediates the relationship between 13-CRA and DOL, but there is no direct evidence that it mediates the relationship between 13-CRA and the prevention of SCC. Determination of the extent to which TGF-α overexpression mediates this relationship and complete validation of TGF-α’s role as a surrogate endpoint biomarker await the results of animal and human trials that utilize reduction in the incidence of SCC as their endpoint.