The anaplastic lymphoma kinase gene(ALK) is mutated approximately 5% of non-small cell lung cancers. Testing for this gene is important because there are drugs known as ALK inhibitors that have been shown to significantly delay the progression of ALK-mutated lung cancers. There are a number of ways to test for the presence of the ALK gene in lung cancer biopsy tissue. One method involves making slides and staining them to detect the ALK protein. This is called immunohistochemistry. Another method called fluorescence in situ hybridization(FISH)is used to detect rearrangements of the ALK gene associated with lung cancer. Although both these tests are widely used to test for ALK gene abnormalities, the techniques may not always find the ALK gene mutation because they are not sensitive enough or not enough cancer cells are present in the lung biopsy.