NRG1 and neoplasm: The NRG1-HER3-PI3K signaling pathwayhas been identified to playa role in promoting brain metastasis outgrowth and therapy resistance,making the targeting of HER3 in combination with a standard systemicdrug a logical approach.17 However, itis possible that the HER3-targeted nanomedicine employed here maynot have adequately suppressed HER3-PI3K signaling in tumor regionsthat have poor drug access.