In this patient, while being clonally related to the adenocarcinoma and not showing any coding mutations in MHC-I genes, the transformed SCLC exhibited substantially reduced expression of components of the MHC-I APP, including the MHC-I heavy chain, β2-microglobulin, and the immunoproteasome component LMP7 (encoded by PSMB8) (Figures 6E and S6D). This evidence concerns the gene APP and small cell lung carcinoma.