Historically we used to classify lung cancer into two large groups called small cell carcinoma and non-small cell carcinoma. We did that for over 50 years, I think, because we had only two groups of treatments for these two particular types of lung cancers.
Now we are learning that approximately 54% or 55% of lung cancers, especially the subtype called adenocarcinoma, have some mutations, some genomic changes, that are called driving mutations, the ones that drive the behaviour of the cancer. One of the most common ones is EGFR. This is a receptor on the surface of the tumour that changes the behaviour of the tumour cells to make them divide uncontrollably and therefore be more able to grow and to metastasize.
We test for this particular EGFR biomarker because several groups of drugs called EGFR tyrosine kinase inhibitors have been developed and are available on the market, including on the Canadian market, for lung cancer patients, but only for those who present this particular mutation.
Testing for EGFR and ALK is completely different. The testing is done at different levels. For example, EGFR mutation testing is a molecular test. It's a test that looks at the DNA signature of the tumour, at the EGFR gene, to identify this particular mutation that makes the tumour more susceptible to certain drugs.
ALK or ALKi, which is a rearrangement in the tumour's genomic signature, is identified in the laboratory through completely different types of tests that we call immunohistochemistry and fluorescence in situ hybridization.
One aspect I would like to bring up, which I think will be of interest to this committee, is the fact that the drug that helps the patients with ALK rearrangement, called crizotinib, was first approved in the United States by the FDA for patients who have the ALK rearrangement only according to this particular fluorescence in situ hybridization test. Now, this is a highly specialized test. It is expensive. It is time-consuming, and it requires technical and professional expertise. Knowing that you cannot really screen a large number of lung cancer patients to identify a relatively small number of them—we're talking about 5% of lung cancer patients—who have this ALK rearrangement, in Canada we worked together at the national level to design a type of testing that used immunohistochemistry as a screen, followed by confirmation through this more specialized fluorescence in situ hybridization or FISH test. This particular exercise allowed us to screen using a much faster and less expensive test like immunohistochemistry to identify the 95% negative patients, and to confirm only the 5% positive ones using the more expensive test. This is a type of testing that later on was also implemented in other countries like Japan and France and many other European countries that really took into consideration the balance between the scientific reality and the reality of their health care system.