Primary resistance to crizotinib treatment in a non-small cell lung cancer patient with an EML4-ALK rearrangement:a case report

Crizotinib,a small molecular tyrosine kinase inhibitor,manifests dramatic responses in patients with non-small cell lung cancer with echinoderm microtubule associated protein like 4-anaplastic lymphoma kinase(EML4-ALK)rearrangements.ALK gene point mutation is the primary mechanism of acquired crizotinib resistance;however,the intrinsic mechanism is not fully understood.Here,we report a patient with a low mutant allele fraction(MAF)of EML4-ALK rearrangement,who experienced primary resistance to crizotinib treatment.The patient was a 66-year-old Chinese man,who had a history of metastatic lung cancer and was treated with first-and third-generation epidermal growth factor receptor tyrosine kinase inhibitors(EGFR TKIs).After 14 months of osimertinib treatment,his disease progressed,and next-generation sequencing was performed from a liquid biopsy of the patient’s blood.An EML4-ALK rearrangement was found and crizotinib was administered.The patient’s lung lesions continued to progress after one month of crizotinib treatment,and pemetrexed-bevacizumab was initiated.After two cycles of chemotherapy,the metastatic cancers shrunk,and the patient maintained stable disease at his last follow-up.EML4-ALK rearrangements can happen in patients with EGFR-positive NSCLC,after acquired resistance to EGFR TKI treatment.The EGFR T790M and C797G mutations occur in cis is a critical mechanism of resistance to osimertinib therapy.The MAF of EML4-ALK rearrangements in cancer cells might be a predictive factor for crizotinib treatment.