Isolated 5′ Signals Are an Atypical Pattern To Be Considered as Positive for ALK Rearrangement: A Brief Report of Three Cases and Review of the Literature1

Anaplastic lymphoma kinase ( ALK ) rearrangement is reported in 3% to 8% of patients with lung adenocarcinoma and can be detected by fluorescent in situ hybridization (FISH) or indirectly by immunohistochemistry. In FISH assay, isolated 5′ signal (loss of 3′ signal) is usually considered negative. We report three young nonsmoking patients with stage IV lung adenocarcinoma. Strong ALK expression in tumor cells detected by immunohistochemistry was observed in all cases, but FISH revealed an isolated 5′ signal pattern. Massive parallel “next-generation” sequencing was performed in two patients and confirmed ALK rearrangement. The three patients were treated and responded to crizotinib after 14, 10, and 31 months.