Tumor Shrinkage With Combination of Alectinib and Trastuzumab in a Patient With ALK-Rearranged Non-small Cell Lung Cancer Harboring HER2-Amplification as an Acquired Resistance Mechanism to ALK Inhibitor Therapy.

Clinical Practice Points • HER2 amplification is an acquired resistance mechanism in ALK-rearranged non–small cell lung cancer. • FISH analysis revealed a minor subclone of HER2-amplified cells before becoming the dominant resistance mechanism. • Combination of HER2 and ALK therapies may be an effective treatment approach for ALK-rearranged NSCLC with acquired HER2 amplification.