Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) hereditary diffuse gastric cancer ?
    ### Response:
    Hereditary diffuse gastric cancer (HDGC) is an inherited disorder that greatly increases the chance of developing a form of stomach (gastric) cancer. In this form, known as diffuse gastric cancer, there is no solid tumor. Instead cancerous (malignant) cells multiply underneath the stomach lining, making the lining thick and rigid.
    