They proposed the following theories: free radicals cause toxicity, which is the main cause of cancer; uric acid protects against malignancy by inhibiting the formation of free radicals; and low serum uric acid in patients with oral cancer may be caused by interleukin-6 (IL-6) and tumor necrosis factor (TNF) secreted in patients with malignancy. This evidence concerns the gene TNF and lip and oral cavity carcinoma.