The main characteristic of “IgG4-related disease” is that it “looks like a tumor but is not a tumor”. The most common manifestation is swelling of tissues or organs, or the formation of localized masses, which can occur anywhere in the body. The New England Journal of Medicine published an article titled “IgG4-related Diseases”, which gave a uniform name to a very difficult group of “anonymous” diseases. Medicine knows no bounds, and from time to time some very difficult diseases are presented to physicians. How difficult is it? “Anonymous” diseases! Doctors have no way to make a diagnosis and “shout” their name because the disease has not yet been named. In February of this year, the New England Journal of Medicine, the most important journal in the medical field, published an article entitled “IgG4-associated diseases”, which gave a uniform name to a very difficult category of “unnamed” diseases. Although “IgG4-associated disease” is a “new” disease recognized only in the 21st century, it is actually a long-standing and not uncommon disease in human history. At the end of the last century, various subtypes of the human immunoglobulin IgG came to the attention of researchers. The earliest interest in IgG4 came from gastroenterologists, who discovered around 2000 that an autoimmune pancreatitis was closely related to IgG4, a subtype of IgG. This pancreatitis presented with an enlarged pancreas and was often diagnosed as pancreatic cancer by ultrasound and CT or MRI, but a pathological biopsy could not find cancer cells. Several years later, physicians in various disciplines have also successively found that swelling, inflammation, fibrosis and other changes in various tissues and organs are associated with IgG4. The clinical manifestations vary greatly due to the location of the damage, but one common feature is that IgG4 is increased in the blood and pathological examinations reveal an increase in IgG4-positive cells. In the past decade, doctors have been describing these diseases under different names in international academic journals, and since 2010, more scholars have been using the term “IgG4-related diseases”. It was not until February of this year that the New England Journal of Medicine settled on a unified name for this type of disease. The “unknown” disease has since become a common rheumatology disease. The main characteristic of “IgG4-related disease” is that it “looks like a tumor, but is not a tumor”. The most common manifestation is the swelling of tissues or organs, or the formation of localized masses, which can occur in any part of the body. It is often misidentified as a tumor, no matter it is an ultrasound examination of hundreds of dollars or a CT or MRI examination of thousands of dollars. What’s worse, even PET-CT, which costs nearly 10,000 yuan for a single examination and is called the most authoritative test to determine tumors, often misclassifies IgG4-related diseases as malignant tumors. However, pathological biopsy denies the diagnosis of tumor. In the past, this kind of “John Doe” disease was investigated and investigated without a conclusion, not because the doctor was incompetent, but because the doctor could not “call” the name of this “John Doe”. These patients may have a good outcome if they see a rheumatologist with some experience and experience. More patients may be transferred from hospital to hospital and department to department and die without knowing what disease they have. IgG4-related diseases involving internal organs (such as pancreas, kidneys, liver, lungs, brain, intestines, and lymph nodes throughout the body) are mostly fatal if they are not diagnosed and treated in a timely manner. However, if timely diagnosis and appropriate immunotherapy are provided, most of them have a good prognosis, and half of them can reach a “cured” state with long-term drug withdrawal. These patients, who were already on the brink of death, were intercepted by doctors and survived or recovered. Although “IgG4-related disease” is a newly named disease, it is not uncommon in clinical practice, and if this test is carried out, it will not only save many desperate “tumor patients”, but also eliminate the cost of various tests due to unknown diagnosis. If this test is carried out, it will not only save many desperate “tumor patients”, but also eliminate the cost of various tests due to unknown diagnosis.