Because recent evidence revealed that PD-1 and PD-L1 levels in several tumors may be relevant prognostic factors [17,28,29,30], our investigation aimed to discover if soluble forms of immunomodulatory molecules, such as PD-1, PD-L1, BTN3A1, and pan-BTN3As, may be helpful in predicting the survival of metastatic GIST (mGIST) patients, in order to obtain significant information about the clinical evolution of disease. Here, BTN3A1 is linked to gastrointestinal stromal tumor.