(1) Nature and origin Pediatric tumors are in the process of growth and development, and there are congenital factors and metabolic functions of individual growth, so the types of pediatric tumors are significantly different from those of adults. Most of them are misshapen tumors rather than true tumors. They are tumor-like malformations, such as hemangiomas, lymphangioleiomas and multiple lipomas, formed by overgrowth and structural disorder of one or several tissues at the site of occurrence. Many tumors have the dual characteristics of tumor and malformation, such as teratoma and hemangioma. The histomorphological characteristics of pediatric benign tumors are more cellular components, deep nuclear staining, and active nuclear division; because their tissues are generally in immature state, they grow and proliferate faster. The prevalent tissues of pediatric malignant tumors are concentrated in the hematopoietic system, central and sympathetic nervous system, soft tissues, bone and kidney, all of which are of non-epithelial origin. Most of them originate from embryonic residual tissues and mesoderm and occur from immature cells, so they are mainly embryonic tumors and sarcomas. Their structures are similar to embryonic organs when they are first formed, with incomplete cell differentiation and rapid expansion; they are characterized by high malignancy, rapid growth, early metastasis and poor prognosis. (2) Morbidity In recent years, the incidence of pediatric malignant tumors has gradually increased. Among them, malignant lymphoma, embryonal tumor, hepatocellular carcinoma and adenocarcinoma of gastrointestinal tract all have obvious gender tendency and are mostly seen in males. The age distribution of malignant lymphoma, embryonal tumor, hepatoblastoma, osteosarcoma, thyroid cancer and gastrointestinal adenocarcinoma is decreasing, 42.9% of the cases occur within 3 years of age. This is in line with the characteristic that “youthful” malignant tumors are mostly seen in prepubertal period. Among them, nephroblastoma, malignant lymphoma and neuroblastoma ranked the first three. (3) Clinical characteristics The age of onset is mainly concentrated in early childhood within 5 years old. And the growth rate is rapid. For example, various types of malignant tumors that are more common in infants and young children may appear to be malignant and infiltrate and grow rapidly into the surrounding tissues, but never metastasize; some of them may recede naturally, and hemangiomas have such characteristics. Most malignant solid tumors are noted for their painless masses that grow rapidly within a short period of time, but their premonitory symptoms are not obvious, and there is rarely any clinically significant anemia or wasting until a more advanced stage when cachexia suddenly appears. Many tumors can invade or metastasize to adjacent tissues or lymph nodes at an early stage, or metastasize to the lung, bone and ilium or brain via blood flow. However, in 2% to 5% of cases, neuroblastoma may mature into a benign ganglioneuroblastoma. Although most teratomas are benign, 15% can be malignant. Some tumors are often associated with other malformations, such as nephroblastoma with aniridia, unilateral limb hypertrophy, sacrococcygeal teratoma combined with cleft palate and spinal art deformity, etc. Malignant tumors within 1 year of age are best treated. Any solid masses in pediatric patients must be treated as malignant, avoiding too much searching. After proper examination and preparation, they should be removed early and finally confirmed by pathological tissue examination and then given the necessary treatment. The recurrence of malignant tumor mostly occurs in six months after surgery, but the time of recurrence can be prolonged with the addition of chemotherapy, and if it does not recur for more than 3 years, there is hope for cure. (4) Staging and its significance Staging of tumor development according to the growth range and degree of spread of primary malignant tumor is an important guiding significance for the development of treatment plan, analysis of efficacy and estimation of prognosis. Internationally, there are different systems of respective staging methods. The TNM classification method of the International Association Against Cancer is based on preoperative clinical and radiological examination, with the intraoperative findings and histological examination as well as regional lymph node metastasis, and the various conditions are combined and divided into four stages. This method is also applicable to pediatric patients. However, many malignant tumors have their own clinical characteristics, and in order to facilitate clinical research, many groups have conducted more concise and practical clinical staging of various tumors, such as the Evans staging method for neuroblastoma. All staging methods must be determined after examination according to the prescribed items. The treatment plan is developed after staging, which facilitates the analysis and comparison of efficacy. Staging can be continuously improved and enhanced. (5) Tumor markers The detection of tumor markers (Chi) plays an important role in the early diagnosis and follow-up of tumor efficacy. Due to the physiological and pathological characteristics of pediatric patients, the ratio of tumor weight to body weight is greater than that of adults, and the diagnostic positivity rate of some tumor markers is significantly higher than that of adults, so the test is more clinically significant. In recent years, with the development of related disciplines, the research of tumor markers has progressed faster. At present, the markers commonly used for clinical efficacy monitoring are AFP, NSE, LDH, CEA and so on. Once the value of these markers is found to rise clinically, further examination is needed to clarify the recurrence and give appropriate treatment. (6) Comprehensive treatment The current treatment for malignant tumors is still centered on the so-called four major therapies, namely surgery, chemotherapy, radiotherapy and immunotherapy. Solid tumors are initially confined to specific tissues and organs, however, cancer cells will sooner or later shed from the primary tumor mass into the blood or lymphatic system to reach distant parts of the body and develop metastatic foci. Therefore, surgery and radiation therapy can only be effective when the primary tumor has not metastasized. Many human malignancies are often metastatic before they are clinically detectable, and microcellular metastases with cell counts below 108 are usually undetectable. Therefore, by the time the diagnosis is made clinically, it may be beyond the ability of surgical and radiological treatment. If, in this case, it is incorrectly assumed that the tumor remains localized, recurrence of the tumor after surgery and radiation therapy is most often attributed to metastatic dissemination prior to treatment. It is too late to apply chemotherapy after recurrence. The traditional treatment procedure of surgical resection followed by radiotherapy and finally chemotherapy when the lesion is advanced and incurable has been eliminated. In order to improve the cure rate of solid tumors, it is necessary to carry out the comprehensive design and rational selection of various anti-cancer therapies, that is, to combine chemotherapy with other therapies to develop a comprehensive treatment plan suitable for all stages of tumors. The general principle is that surgery is still the main treatment for those with limited lesions, while surgery and chemotherapy should be used for those with more than localized lesions. If the tumor is huge, chemotherapy can be used first, and then surgery can be performed after the tumor shrinks, which is called delay primary operation; or some of the tumor can be removed or biopsied during the first operation, and then second look operation can be performed after a period of chemotherapy. In advanced cases, the hope is that the primary site will be removed and other therapies will be used to improve the outcome. The main treatment for solid tumors is still surgery. The current progress of surgical treatment for solid tumors is to move from the pursuit of surgical safety to the pursuit of radical enlarged resection, combined surgery with other therapies and adequate reduction surgery if necessary, i.e., the three principles of safety, preservation of function and radicality are required. Extended surgery still refers to the resection of the primary tumor organ, the whole lymph node system, and the resection of surrounding suspicious tissues. Reduction surgery refers to the resection of as small an area as possible in order to preserve the function. Depending on the condition of the child, the nature of the tumor and the extent of its spread, the proper use of expansion and reduction surgery is a great advancement. This is based on the improved understanding of tumor pathophysiology, the development of various diagnostic methods, the emergence of new medical devices, advances in preoperative, intraoperative, and postoperative management, the application of nutritional therapy, and the evaluation of long-term outcomes, all of which play an important role in the improvement of surgical therapies. The treatment plan for pediatric malignant tumors should especially take into account the ability to save lives while preserving normal growth and development. Although only 2% of pediatric patients have malignant tumors, once a child’s life is saved from cancer, it can be preserved for life. Therefore, it is more important for medical personnel to treat pediatric malignant tumor, no matter it is early or late, they should always have a positive and optimistic attitude, use various methods to carry out comprehensive treatment, and strive for cure instead of palliation, and their efficacy will surely improve gradually and survival rate will rise. (7) Prognosis The prognosis of pediatric malignant solid tumors is closely related to pathological type, lesion location, clinical stage, age of onset and other factors. The 5-year survival rate was 100% for stage I cases, 74.5% for stage II, 44.5% for stage III, and no 5-year survival for stage IV and stage cases. Malignant tumors such as thyroid cancer, vaginal rhabdomyosarcoma and testicular embryonal carcinoma have better prognosis due to easy resection, late metastasis and barrier effect, while malignant tumors of liver and bone tissues have poor prognosis. With the continuous updating of malignant tumor diagnosis and treatment techniques and concepts, the survival rate of pediatric malignant born solid tumors has been increasing year by year. In the past 10 years, the 5-year survival rate has increased from 33.6% in the 1970s to 43.7% with the continuous improvement of preoperative chemotherapy, multiple radical resections and comprehensive treatment protocols.