Different histopathology but the same clonality: ALK rearrangement in a patient with metastatic non-small-cell lung cancer.

EML4-ALK rearrangement is detected in 2% to 7% of lung adenocarcinomas, these tumors are sensitive to crizotinib. The histologic feature of ALK translocated non-small-cell lung cancer (NSCLC) has been studied, presence of signet-ring cells was a powerful histologic indicator of ALK rearrangement, and this characteristic histology was present both in primary sites and metastases. However, the case we discribed here has different histomorphology in primary sites and metastases, but has the same genotype which both present ALK rearrangement, while absent of EGFR mutation, KRAS mutation and ROS1 rearrangement. This histologic heterogeneity may be a supplement of the histologic feature of ALK rearranged tumor. Moreover, genomic analysis can help distinguish clonal tumors from independent primaries.