Overview: The incidence of leukemia in China is 3-4 per 100,000 population, of which chronic granulocytic leukemia (CML) accounts for 15% of leukemia patients with a natural course of 3-5 years. Chronic granulocytic leukemia, a malignant hematologic neoplasm of bone marrow origin, has a slow onset and can develop in all age groups, with a predominance in middle age. CML is divided into chronic phase, accelerated phase and acute phase, and most patients are in the chronic phase when found. Case: Six months ago, a 56-year-old female patient was found to have a high white blood cell count of >10,000 cells/microliter occasionally during a physical examination. She had no discomfort and after repeated examinations, infectious diseases were ruled out; several routine blood tests showed that the leukocyte count was always higher than normal, and only a slight thickening of the spleen was found on ultrasound examination. In order to find out the cause of the increased white blood cells, she came to the hematology department. After careful analysis of her previous test results, the doctor concluded that to clarify the cause of the leukocyte increase, a systematic examination of the patient’s hematopoietic function for abnormalities was needed, in addition to ruling out inflammatory infections as the cause. In the field of hematology, there is a group of diseases collectively known as “myeloproliferative disorders”, which include four specific diseases: chronic granulocytic leukemia, true erythrocytosis, primary thrombocytosis, and primary myelofibrosis. In the early stages of these diseases, there is no obvious not feeling, so they are often easily overlooked. To clarify the underlying cause of this patient’s morbidity, we recommended that she undergo a series of tests to clarify the diagnosis: bone marrow aspiration, karyotype analysis, and fusion gene testing. 1 week later, her test results showed a t(9:22) chromosomal translocation and a positive BCR/ABL fusion gene. Diagnosis and analysis: The actual implication of this result is that humans have 23 pairs of chromosomes, and her chromosome 9 and 22 each broke a small segment, and then during chromosome repair, the segment of 9 was attached to 22 and the segment of 22 was attached to 9, which also resulted in a new gene BCR/ABL. this new gene encodes a new BCR/ABL fusion This new gene encodes a new BCR/ABL fusion protein. This new gene encodes a new BCR/ABL fusion protein, which has a sustained, strong tyrosine kinase activity that causes cells to proliferate and divide, leading to an increase in white blood cells. Therefore, this patient was diagnosed with “chronic granulocytic leukemia”. Treatment: In the past, CML was treated with hydroxyurea, interferon, or a combination of low-dose chemotherapy to control the cell count. The latest international development is the use of imatinib mesylate (Gleevec, STI571) for targeted therapy. The main mechanism of this drug is to specifically bind to the patient’s BCR/ABL protein and inhibit the tyrosine kinase activity of this cancer protein, thereby causing apoptosis of CML leukemia cells and achieving disease remission. This therapeutic agent significantly extends the life span (survival time) of patients and has become the preferred method of CML treatment. Judgment of efficacy: Since the cause of CML is clear and mainly produces abnormal BCR/ABL fusion genes; the targeted drugs also target mainly BCR/ABL proteins, so the specific index for judging the efficacy of CML is the number of BCR/ABL fusion genes. In clinical practice, it is recommended to test the change in the number of BCR/ABL fusion genes at least once every 3-6 months after treatment with drugs. At present, we mainly test the number of fusion gene reduction at 3, 6, 12 and 18 months after drug administration, and compare the trend of BCR/ABL fusion gene change at the above time points, so as to judge the effectiveness of treatment. It also predicts the future survival time of patients based on the changes in the number of BCR/ABL genes. Detection and monitoring of fusion genes: For chronic granulocytic leukemia, nested polymerase chain reaction (n-PCR) and real-time fluorescence quantitative PCR techniques are mainly used to detect the copy number changes of BCR/ABL fusion genes. Our hematology department has carried out karyotype analysis techniques, as well as clinical genetic diagnosis techniques. The hematology laboratory has constructed and completed the cloning of more than 10 detection genes and plasmid construction of standards, designed more than 50 primers for leukemia genes and established a detection technology system that can provide accurate leukemia gene diagnostic techniques mainly for qualitative detection of leukemia fusion genes to assist in the diagnosis of leukemia; monitoring the response of leukemia patients to chemotherapy and other treatments and evaluating the efficacy. For patients with slow-growing leukemia, detection and monitoring of the copy number of the characteristic fusion gene BCR-ABL can determine the efficacy of treatment and long-term prognosis of patients. The application of leukemia gene diagnosis technology has enabled the treatment of some hematological diseases to enter the mode of “individualized treatment of leukemia based on molecular genotyping”, which has significantly improved the efficacy and shortened the treatment time for some patients.