The core of medicine is the diagnosis and treatment of diseases, and correct diagnosis is the prerequisite for any effective treatment. With the rapid development of science and technology, there are numerous diagnostic tools for diseases, and pathological diagnosis is the first one in terms of accuracy. When it comes to pathological diagnosis, many people find it unfamiliar. In a nutshell, pathological diagnosis is a direct judgment of a disease made by a pathologist using pathological theories and techniques, combined with personal professional experience, by observing the cells and tissue structure of the lesion with the naked eye and under a microscope, and by referring to the patient’s clinical data. Compared with the long history of human beings, the history of pathological diagnosis is not long. In the 17th century, there were ancient scholars who observed lesions with the naked eye and magnifying glass, but it was not until the mid-19th century when scholars began to observe the cells and tissue structures of lesions with microscopes that the era of pathology diagnosis was created. Today, the development of immunology, cytogenetics and molecular biology has further advanced the development of pathology. The results of pathology diagnosis are related to the clinician’s treatment plan and prognosis of the patient, and are of key, if not decisive, importance in summarizing the clinical work. Because of this, pathologists are known as “doctor’s doctor” (doctor’s doctor).