The present invention relates to methods for preventing the development of cancer or neurodegenerative diseases by administering N-Acetylcysteine (NAC), melatonin, or a combination thereof. The present invention also relates to methods for diagnosing cancer and/or neurdegenerative disease by detecting or determining the amount of dopamine metabolites, 4-CE, 2-CE, methylation of CE or CE-Q conjugates.
