Stage IV ERBB2-Mutated Lung Adenocarcinoma Responding to HER2-Targeted Therapy

What happened, in summary

A 67-year-old Asian woman who had never smoked was diagnosed with Stage IV lung adenocarcinoma with biopsy-proven involvement of both lungs. Molecular testing identified an ERBB2 exon 20 insertion. She first received carboplatin and pemetrexed for 3 months, followed by 6 months of pemetrexed maintenance. When the cancer progressed, she started trastuzumab plus docetaxel. This combination produced a partial response and controlled the disease for 8 months before another progression. Her treatment was then changed to afatinib. Imaging after 1 month showed a response, but she could not continue the drug because her insurance denied coverage. She therefore returned to trastuzumab-based therapy. Her course included measurable disease control with both chemotherapy and HER2-directed treatment, while access to medication directly influenced the next treatment decision.