PTGS2 and Erythema: Aligned with the oral mucosal erythema, erosions, and ulcerations in 5-FU treated mice (group C), the present study demonstrates that expression of Cyclooxygenase-2 (COX-2), a key inducible enzyme upregulated by inflammatory stimuli, was upregulated in the oral and intestinal mucosa of mice treated with 5-FU (Fig. 8).