In addition, SCLC ITH was further complicated by heterogeneous expression of MHC-I in SCLC cell populations, as HLA-A, HLA-B, and HLA-C were low in six clusters and high in five clusters according to our scRNA-seq data, and the observation that SCLC cancer cells express MHC-I molecules was confirmed by our spatial proteomics data. Here, HLA-B is linked to small cell lung carcinoma.