A Case of Lung Adenocarcinoma Response to Alectinib Harboring a Rare EML4-ALK Variant, Exon 6 of EML4 Fused to Exon 18 of ALK.

More than 20 types of ALK fusion variant subtypes have been identified, including different fusion partner genes or EML4-ALK fusions with different breakpoints. However, different ALK fusions show different sensitivities to ALK-tyrosine kinase inhibitors (ALK-TKIs) and the emergence of rare fusions brings great challenges to the target therapy in clinic. We report a rare EML4-ALK (E6;A18) fusion in a patient with lung adenocarcinoma that responded well to alectinib. This is the second case of this rare variant reported but the first report of response to an ALK-TKI. This evidence is the first to show that alectinib may be effective for this rare fusion type of non-small cell lung cancer, and these findings have important implications for drug selection in patients with this subtype. Further studies are needed to understand the function of this variant.