Microsatellite instability (MSI) is a tumor-agnostic marker of response to PD-1/PD-L1 blockade [29] and can be found in GEP mixed adeno-neuroendocrine carcinoma (MANEC), while it is rare in G1-G2 GEP-NET [50,51]. The gene discussed is PDCD1; the disease is neoplasm.