2012/08/31 12:34

Case study 9 (methods)

EGFR (epidermal growth factor receptor) mutations are the best predictor of response to EGFR inhibitors in lung cancer. However, the cost and complexity of molecular techniques to detect these mutations have prevented most individuals in the pathology community from testing for these mutations in newly diagnosed cases of lung adenocarcinoma. What is the MOST promising strategy to implement EGFR testing in a wider patient distribution?

Choices
    •    Immunohistochemistry for total EGFR expression
    •    Chromogenic or fluorescein in situ hybridization analysis for EGFR
    •    MicroRNA
    •    Isolation of circulating tumor cells
    •    Immunohistochemical stains for mutant EGFR protein
    •    
Explanation
Immunohistochemical analysis is a technology available in the vast majority of pathology laboratories. Recently commercially available antibodies that detect specific EGFR mutants have become available. These are a pair of antibodies that detect L858R mutation in exon 21 and 15 base-pair deletions in exon 19—the most common mutations encountered in the EGFR genes. These antibodies have been tested in an experimental setting1 with good results. They showed a positive predictive value of 100% (no false-positives were detected); however, these antibodies cannot detect other uncommon mutations or deletions in the gene. Thus, a negative result does not exclude the possibility of mutated EGFR.
Reference
    1.    Brevet M, Arcila M, Ladanyi M. Assessment of EGFR mutation status in lung adenocarcinoma by immunohistochemistry using antibodies specific to the two major forms of mutant EGFR. J Molec Diagn. 2010;12:169-176.


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What is the BEST method for the diagnosis of EML4-ALK (echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase) translocation used today?

1. Fluorescence insitu hybridization (FISH)
2. Immunohistochemistry
3. Direct sequencing
4. Micro RNA
5. PCR

Explanation:

Specific detection of ALK-rearrangement is best done by FISH. The same commercially available probe used for the detection of ALK translocation in ALK-rearranged anaplastic large-cell lymphoma can efficiently detect ALK translocations in pulmonary adenocarcinoma.

In contrast, the antibody used to detect ALK rearrangement in lymphoma does not work in pulmonary adenocarcinoma. Currently, there is no commercially available antibody that can be used for the diagnosis of ALK translocation in lung cancer, but there are some antibodies being used experimentally that appear to have good specificity and hopefully will become available commercially in the near future. This would enable most pathologists to test for rearranged ALK in their samples. ALK rearrangement also can be detected by PCR-based techniques; however, there are at least 11 variants of EML4-ALK fusion genes, making a PCR-based diagnosis very challenging.

EML4-ALK translocation can be seen in approximately 5% of pulmonary adenocarcinomas, and this percentage can be enriched in tumors showing a histologic pattern of solid adenocarcinoma with at least 10% of signet ring cells. This translocation can be targeted by a specific drug that is undergoing clinical trials (crizotininb).1

Reference
    1.    Takaaki S, Rodig SJ, Chirieac LR, Jänne PA. The biology and treatment of EML4-ALK non-small cell lung cancer. Eur J Cancer. 2010;46:1773-1780.


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