ALK immunohistochemistry is highly sensitive and specific for the detection of ALK translocated lung adenocarcinomas: lessons from an audit of lung cancer molecular testing

: Background The approval of novel targeted treatments for epidermal growth factor receptor (EGFR)-positive and anaplastic lymphoma kinase (ALK)-positive non-small cell lung cancer has led to the increased requirement for mutation testing. Results We report our experience of ALK testing with immunohistochemistry (IHC) and fluorescence in-situ hybridisation (FISH) and present the prevalence of EGFR, Kirsten rat sarcoma 2 viral oncogene homolog (KRAS) and ALK mutations. From January 2011 to May 2014, we found mutation rates of EGFR, KRAS and ALK to be 10.4% (67/643), 35.8% (86/240) and 2.3% (7/304), respectively. ALK-rearrangements were found to be associated with never smokers (p < 0.001) and younger patients (≤ 50 years old) (p < 0.001). ALK IHC protein expression in tumour cells is 100% sensitive (7 IHC+/7 FISH+) and 96.6% specific (113 IHC-/117 FISH-) for ALK-rearrangements by FISH. ALK-rearranged tumours were wildtype for EGFR and KRAS. Conclusion Our findings support the use of ALK protein expression and KRAS mutation testing as part of the molecular diagnostic algorithm for lung adenocarcinomas.