Free radicals can also be induced by oxidative stress. Low levels of antioxidants such as superoxide dismutase, catalase, ceruloplasmin may also indicate oxidative stress, as do elevated levels of tumor markers such as aspartate transaminase, alanine transaminase, alkaline phosphatase and total sialic acid in circulation. So any or all of these abnormal levels may be indicative of the presence of tumors, e.g., cervical carcinoma. HTH.