Immunohistochemistry as Effective as DNA Hybridization for Detecting ALK Rearrangement in Lung Cancer Patients

The ALK gene can be oncogenic in three ways: by forming a fusion gene with any of several other genes, by gaining additional gene copies, or with mutations of the actual DNA code for the gene itself. The EML4-ALK (echinoderm microtubule-associated protein-like 4 anaplastic lymphoma kinase) fusion gene is responsible for approximately 3%–5% of cases of NSCLC. The standard tests used to detect this gene in tumor samples is fluorescence in situ hybridization (FISH), and Reverse Transcriptase-PCR (RT-PCR). The FISH technique utilizes a DNA probe labeled with a fluorescent dye that is hybridized with target DNA, usually chromosome preparations on a microscopic slide. It is used to precisely map genes to a specific region of a chromosome in prepared karyotype, or can enumerate chromosomes, or can detect chromosomal deletions, translocations, or gene amplifications in cancer cells.

As IHC is a less complex and less costly technology than FISH, investigators at the Chinese University of Hong Kong SAR (China) evaluated its practical usefulness for detection of ALK rearrangement in NSCLC ADCs. They tested 373 lung ADCs for ALK rearrangement by IHC and FISH. Multiplex RT-PCR was performed to confirm the fusion variants.

Results showed that 22 of 373 lung ADCs (5.9%) were positive for ALK immunoreactivity. ALK-positive tumor cells demonstrated strong and diffused granular staining in the cytoplasm. All the ALK IHC-positive cases were confirmed to harbor ALK rearrangement, by either FISH, or RT-PCR. Two cases that were positive for ALK protein expression by IHC, but negative by FISH were shown to harbor EML4-ALK variant 1 by RT-PCR. None of the ALK IHC-negative cases was FISH-positive.

These results allowed the investigators to conclude that, "IHC can effectively detect ALK rearrangement in lung cancer. It might provide a reliable and cost-effective diagnostic approach in routine pathologic laboratories for the identification of suitable candidates for ALK-targeted therapy."

The study was published in the July 2013 issue of the Journal of Thoracic Oncology.

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