Small-cell transformation of ALK -rearranged non-small-cell adenocarcinoma of the lung.

Anaplastic lymphoma kinase (ALK) gene rearrangements are present in ∼5% of non-small-cell lung cancers (NSCLCs). These rearrangements occur because of a chromosomal inversion within the short arm of Chromosome 2, which results in the formation of the echinoderm microtubule-associated protein-like 4 (EML4)-ALK fusion oncogene. Whereas NSCLC transformation to SCLC is a rare phenomenon described in epidermal growth factor receptor (EGFR) mutant cancers primarily after treatment with targeted therapy, it is exceedingly rare in ALK-rearranged adenocarcinomas. It is currently unclear what the therapeutic significance of the rearrangement is in this transformed tumor as there is a paucity of medical literature describing follow-up care and outcomes of patients in this rare scenario. We describe a unique case in which a patient with ALK-rearranged adenocarcinoma underwent small-cell transformation at a metastatic site with retained ALK rearrangement and was provided clinical follow-up after treatment with second-generation tyrosine kinase inhibiter (TKI) therapy.