Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Skin Cancer ?
    ### Response:
    Once cancer has been found, the doctor will need to determine the extent, or stage, of the cancer. Through staging, the doctor can tell if the cancer has spread and, if so, to what parts of the body. More tests may be performed to help determine the stage. Knowing the stage of the disease helps you and the doctor plan treatment.
    