APP and lung carcinoma: While our study does not support a role of amyloid precursor protein (APP) or Aβ in BACE1-mediated BM in our models, the importance of BACE1 in modulating EGFR signaling is clear, and future work to evaluate the utility of Aβ as a biomarker for lung cancer BM as a surrogate for BACE1 expression/activity is warranted.