CD44, a multifunctional cell surface adhesion receptor, has been described to be highly expressed in non-NE SCLC cells,35 and is associated with the migration and invasion processes involved in the metastasis of this subtype (Supplementary Fig. S5c).36 Consistent with the results from GEMMs and human SCLC, the high expression of HES1 (Supplementary Fig. S5d), a transcriptional target of the NOTCH signaling pathway, together with the low expression of DLK1 (Supplementary Fig. S5e), indicated an activated NOTCH signaling pathway in this cell population. This evidence concerns the gene CD44 and small cell lung carcinoma.