Identification of targetable oncogenic mutations in non-small cell lung cancer (NSCLC) has been a major advance in cancer treatment. Laboratory techniques to assess human epidermal growth factor receptor 2 (HER2) positivity in NSCLC include immunohistochemistry (IHC) for protein overexpression, fluorescent in situ hybridization (FISH) for gene amplification, and next generation sequencing (NGS) for HER2 gene mutations. These tests have a controversial prognostic and predictive value, with an emerging association between HER2 gene mutations and treatment response to HER2 targeted therapy. We present a case of a woman with metastatic lung adenocarcinoma with HER2 positivity assessed by IHC and FISH, as well as a high gene copy number noted on NGS. She was observed to have significant disease progression following standard first-line platinum doublet chemotherapy. She was started on dual HER2 blockade in the second-line setting, which yielded a great response in the liver with stable disease elsewhere. To our knowledge, this is the first report describing successful use of dual HER2 blockade in metastatic HER2 positive NSCLC. We also review common laboratory techniques for determining HER2 positivity in NSCLC and their clinical applications.