ERBB2 and non-small cell lung carcinoma: CXCR4 and its ligand, stromal-derived-factor-1 (SDF-1; also called CXCL12), may drive metastatic trafficking to the brain [36, 37]. The frequency of brain metastases at diagnosis was similar in NSCLC patients carrying HER2 mutations (19%), compared to patients with KRAS (24%) and EGFR mutations (31%) [35].