Antioxidants are chemicals that neutralize particles called free radicals that can damage DNA. Preventing such damage may help lower cancer risk for some people. However, tumors themselves can contain high levels of free radicals; by eliminating these free radicals, antioxidants may help cancer cells grow. In a laboratory, lung cancer cells treated with the antioxidants vitamin E and acetylcysteine (ACC) multiplied faster than untreated cells. Vitamin E and ACC also increased tumor growth and decreased survival time in mice with lung cancer. The so-called 'tumor suppressor' protein p53 can sense certain free radicals to detect cells with DNA damage and stop their growth. Antioxidants may interfere with this cancer-suppressing mechanism by reducing free radical levels. Taking antioxidants may therefore not be recommended for lung cancer patients and smokers.