This test detects the presence of the BCR-ABL fusion gene, which results from the Philadelphia chromosome translocation t(9;22)(q34;q11). It is a qualitative molecular test, meaning it determines whether the fusion gene is present or absent, without measuring the amount. The test is commonly performed on blood or bone marrow samples and is primarily used in the diagnosis of Chronic Myeloid Leukemia (CML) and certain types of Acute Lymphoblastic Leukemia (ALL). Detection of the BCR-ABL fusion gene confirms the presence of Philadelphia chromosome-positive leukemia and helps guide targeted therapy with tyrosine kinase inhibitors.