Identification of anaplastic lymphoma kinase fusions in clear cell renal cell carcinoma

As one of the most common types of renal cancer, clear cell renal cell carcinoma (ccRCC) in advanced stages constitutes a continued major challenge for uro-oncologists, as the identification of novel driver mutations and the development of novel targeted therapies against them remain an unmet need. Aberrations in anaplastic lymphoma kinase (ALK), a rational therapeutic target, as verified in lung cancer with ALK rearrangement, have been implicated in the pathogenesis of multiple human cancers. In the present study, we screened ALK expression in 87 pathologically defined ccRCCs via immunohistochemistry (IHC) using a newly developed rabbit anti-human ALK monoclonal antibody (clone D5F3). Four patients tested positive for ALK expression, as confirmed by IHC. Among them, 2 patients were further confirmed with fluorescence in situ hybridization (FISH) assay with the use of the Vysis LSI ALK dual color break-apart probe. Furthermore, we detected the existence of the echinoderm microtubule-associated protein-like 4/anaplastic lymphoma kinase (EML4-ALK) (E13:A20, variant 1) fusion gene in tumors from these two patients by using rapid amplification of cDNA ends (RACE)-coupled PCR sequencing and RT-PCR. Notably, we first showed that enforced EML4-ALK expression could significantly promote in vitro proliferation, clonogenic colony formation and apoptosis resistance in HK2 immortalized normal renal tubal epithelial cells and their in vivo outgrowth when injected into immunocompromised nude mice. Importantly, this pro-tumorigenic effect was completely abolished by the ALK-specific inhibitor crizotinib, indicating the potential effectiveness of ALK-specific inhibitors in treating ALK-rearranged ccRCC patients. Our data revealed that ALK fusions exist in adult ccRCC, providing a rationale for ALK inhibitor therapy in selected patients with ccRCC.