SLC44A4 and small cell lung carcinoma: To investigate the differences in gene expression between H128-LM cells and other cell types, we initially analysed RNA-seq data from SCLC brain metastases available in the Gene Expression Omnibus (GEO) database (Series GSE 161,968) and found that SLC44A4, OCLN, IGF2, SLC47A1, and SLC28A3 were significantly upregulated in patients with brain metastases (Fig. 4D).