Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Primary gastrointestinal melanoma ?
    ### Response:
    Primary melanoma of the gastrointestinal (GI) tract refers to a melanoma starting in the stomach, intestines, salivary glands, mouth, esophagus, liver, pancreas, gallbladder, or rectum. Melanoma is a disease in which malignant (cancer) cells form in the melanocytes.
    