Protein methylation has an important role in the regulation of chromatin, gene 
expression and regulation. The protein methyl transferases are genetically 
altered in various human cancers. The enzymes that remove histone methylation 
have led to increased awareness of protein interactions as potential drug 
targets. Specifically, Lysine Specific Demethylases (LSD) removes methylated 
histone H3 lysine 4 (H3K4) and H3 lysine 9 (H3K9) through 
formaldehyde-generating oxidation. It has been reported that LSD1 and its 
downstream targets are involved in tumor-cell growth and metastasis. Functional 
studies of LSD1 indicate that it regulates activation and inhibition of gene 
transcription in the nucleus. Here we made a discussion about the summary of 
histone lysine demethylase and their functions in various human cancers.