<B>The RB1 Problem</B> 

Patients of leiomyosarcoma have been known to have abnormalities with the RB1 gene. A similar problem occurs within other sarcomas but mostly in leiomyosarcoma, malignant fibrous histiocytoma (MFH) and rhabdomyosarcoma. 

<B>How RB1 works</B> 

The result of cell division should be a cloned cell that has the exact same DNA as its parent cell. Cell division is normally allowed to proceed only once the DNA has been proof read and is confirmed to be an exact match. The proof reading is done by enzymes who can repair DNA that hasn't been accurately copied. If the newer DNA is not an exact mirror of the older DNA then enzymes will remove the newer DNA allowing the older DNA to be recopied. 

The cell knows that it is still proof reading by the presence of the Rb protein that is created by the RB1 gene. The Rb protein is like a switch telling the cell to wait until proof reading is completed. When the cell has completed the proof reading phase and corrected all the errors, the Rb protein is phosphorylated allowing the cell to continue on to the next phase of cell division. 

This diagram shows the cascading events leading to the phosphorylation of Rb protein. 
