EGFR and squamous cell carcinoma: Interestingly, considering that EGFR mutation is much more common in lung adenocarcinoma than squamous cell carcinoma, our findings linking DRD1 and EGFR signaling suggest that DRD1's regulation of EGFR is a possible mechanism for DRD1 levels being more prognostic in lung adenocarcinoma than squamous cell carcinoma.