Detection of ALK re-arrangement in non-small cell lung carcinoma: correlation of results by FISH and D5F3 immunohistochemistry

Activating mutations or translocations of the anaplastic lymphoma kinase gene (ALK) have been identified in approximately 5% of non-small cell lung cancers. To determine patients’ eligibility for crizotinib, a tyrosine kinase inhibitor therapy, accurate assessment of ALK rearrangement is required. Fluorescence in situ hybridisation (FISH) analysis is the gold standard for detection of ALK rearrangement, however it is time consuming and expensive as an initial screening method. Reliable triage by ALK immunohisto-chemisty (IHC) would be clinically advantageous, however there has been some concern regarding preservation of antigenicity in pre-cut slides. We compared detection of ALK rearrangment by IHC (Cell Signalling Clone D5F3) and FISH (Vysis ALK break apart probe) on 52 selected cases of non-small cell lung carcinoma. Of eight cases found to be positive by FISH, seven showed positive staining by IHC. No false positive IHC results were found (98% overall concordance). ALK reactivity was preserved in control sections prepared over 3 weeks prior to staining. ALK IHC with antibody D5F3 therefore would appear to be a reliable triage method for detecting ALK gene rearragement, although occasional cases may show discordance; if there is strong clinical suspicion of an ALK-rearranged tumour, FISH testing should not be refused.