1.What is cancer? In medical science, malignant tumors that originate from epithelial tissue are called cancer. If it occurs in squamous epithelial cells, it is called squamous epithelial cell carcinoma, or squamous carcinoma for short. It often occurs in the parts of the body covered by the original squamous epithelium, such as skin, mouth, lips, cervix, vagina, esophagus, larynx, penis, etc. Adenocarcinoma occurs in glandular epithelial cells. It is mostly found in the stomach, intestines, breast, liver, thyroid, salivary gland, bronchus and uterine body. If malignant tumors grow in these organs of human body, they are called skin cancer, stomach cancer, esophageal cancer, intestinal cancer, etc. respectively. Cancer is mostly found in middle-aged and elderly people above 40 years old. From the metastasis route, cancer is mostly metastasized through lymphatic tract. 2.What is tumor? Tumor is a new organism generated by overgrowth or abnormal differentiation of a certain cell group under the long-term effect of certain adverse factors, which forms a lump in the local area. However, unlike normal tissues and cells, it does not grow according to the normal cellular metabolic law, but becomes unrestrained and uncontrolled, resulting in abnormal cellular form, function and metabolism, which can destroy the structure of normal tissues and organs and affect their functions. Malignant tumor cells can also infiltrate and spread to other organs and tissues, and continue to multiply, causing great threat to human body or life. Although lumps are often formed in the process of human growth, they are not always tumors. Therefore, the nature of the mass must be identified in order to achieve correct diagnosis and treatment. 3.What is sarcoma? Malignant tumors originating from mesenchymal tissue (including connective tissue and muscle) are called “sarcoma”. Most of them occur in skin, subcutaneous, periosteum and both ends of long bones. If fibrosarcoma grows rapidly, there is often necrosis and bleeding in the late stage of the tumor, and the cut surface is gray-red and uniformly fine like raw fish. Osteosarcoma is more common in young people and is most common at the ends of the long bones of the extremities, especially at the lower end of the femur, upper end of the tibia and upper end of the humerus. Osteosarcoma develops rapidly and has a short course. It starts to grow in the cortex and gradually develops into the bone marrow cavity, sometimes breaking through the periosteum and invading the surrounding soft tissues, which can easily cause pathological fractures. Smooth muscle tumor, lymphosarcoma, synovial sarcoma, etc. are also common. Bloodstream metastasis can occur at an early stage. 4.What is benign tumor? The cells of some tissues in the body proliferate abnormally and grow swollen, like ballooning, and grow slowly. As the tumor increases continuously, it can squeeze the surrounding tissues, but does not invade the adjacent normal tissues, and the tumor is mostly spherical and nodular. It is easy to be excised cleanly during surgery and does not metastasize, so there is rarely recurrence. This kind of tumor only has the effect of extrusion and obstruction to the local organs and tissues, and generally does not destroy the structure and function of organs, and necrosis and bleeding rarely occur. After surgical resection, after pathological examination, it can be found that the tumor cells are well differentiated, similar to normal tissue cells, without nuclear division or sparse nuclear division, and without pathological nuclear division. 5.Can tumors be prevented? Can tumors be prevented? Hegson and Richard Doyle have estimated that 80% of tumors are preventable. Doyle has estimated that 80%-90% of human tumors are caused by external environmental factors. The environment here refers to the effect of direct exposure to certain specific carcinogenic substances (chemical, physical, biological) and poor lifestyle (diet, smoking, childbirth) on cancer. Therefore, avoiding exposure to carcinogenic substances and changing poor lifestyle may be effective in preventing the occurrence of cancer. Cervical cancer used to account for more than 60% of gynecological tumors and is the gynecological malignancy with the highest incidence in China. The occurrence of cervical cancer is related to early and close childbirth and unclean sexual life. Before the occurrence of cervical cancer, there are often changes such as chronic cervicitis, cervical erosion, polyps, papilloma, acromegaly and cervical epithelial atypical hyperplasia. Accordingly, China’s health administrative departments actively promote late marriage and less childbearing, strengthen premarital sexual health education, advocate the habit of washing the external genitalia of both spouses before sex, and widely carry out cervical smear screening, so that the incidence of cervical cancer has dropped significantly in recent years. Due to the long-term and regular insistence of Shanghai textile workers on census and treatment of precancerous lesions, the survey of female workers aged 20-55 from 1958 to 1980 showed that the incidence of cervical cancer dropped by 91.6%, the age of cancer patients found in the census was postponed by 8.7 years, the proportion of early-stage cancer increased significantly, and no advanced cancer was found in the last 7 years, and the 5-year survival rate and 20-year survival rate of the 520 cases of cervical cancer detected were 95.9 percent respectively. The 5-year survival rate and 20-year survival rate of 520 cases of cervical cancer detected were 95.9% and 86.1%, respectively. The incidence and mortality rates of cervical cancer were significantly reduced. Cigarette smoking has been recognized as the most important risk factor for lung cancer. Cigarette smokers have a higher risk than cigar or pipe smokers, and those who smoke cigarettes without a filter or high-tar cigarettes have a higher risk than those who smoke filtered or low-tar cigarettes. The risk of lung cancer increases with the number of years of smoking and the amount of cigarettes smoked per day. In areas where the smoking habit of the population has been formed for a long time, the attributable risk of smoking to the lung cancer population is generally above 80%, and this indicator was 70% to 80% for men in Shanghai in the 1980s. The risk of lung cancer decreases significantly after quitting smoking. It has been reported that the incidence of lung cancer in smokers is 20 times higher than that in non-smokers, and 2.5 years after quitting, the incidence of lung cancer is about 10 times higher than that in non-smokers, 7.5 years after quitting is 5 times, and 15 years after quitting is less than 2 times. This indicates that the incidence of lung cancer can be effectively reduced by eliminating the carcinogenic factors in cigarette smoke through preventive measures. 6.Can tumors be hereditary? Tumors are hereditary, but the degree of hereditary tendency varies, and in fact, all human tumors show a high tendency to occur in a certain population. For example, the incidence of nasopharyngeal cancer among Chinese is much higher than that of Japanese and Americans. In China, the incidence rate of nasopharyngeal cancer is the highest among Cantonese, and the incidence rate of nasopharyngeal cancer among Cantonese who have moved to Shanghai for more than 10 years is still 3.64 times higher than that of local residents in Shanghai; conversely, the incidence rate of nasopharyngeal cancer among foreigners who have moved to Guangdong is still much lower than that of local Cantonese. Studies have shown that some cancers are associated with a genetic alteration, and the most common gene mutation and alteration in human cancers is the oncogene p53. p53 mutations or alterations have been reported in 70% of colon cancers, 30% to 50% of breast cancers, 50% of lung cancers, and all small cell lung cancers. Tumor susceptibility genes are present in certain cancer patients. For example, women with the breast cancer susceptibility gene BRCAl on chromosome 17 have a much higher risk of developing breast cancer than women without the BRCA1 gene. Certain childhood tumors, such as retinoblastoma, neuroblastoma, nephroblastoma, and leukemia, are seen in both parent and child generations, and patients have genetic defects that are autosomal dominant; this hereditary cancer is the best example of how tumors can be inherited. Patients usually develop the tumor at an early age, often in infancy, often bilaterally or multiple times, and there is no significant gender difference. When more members of a family develop the same tumor or tumors, the family is called a cancer family. The first and most detailed cancer family in the world is called “G family” according to the first letter of their surname. From 1895 to 1976, a total of 5 surveys, 7 generations, 10 clades and 842 descendants were conducted over 80 years. It was found that there were 7 high cancer clades among the 10 clades, and the cancer incidence rate was as high as 35%, and the incidence rate was similar for men and women, and the age of incidence was mostly 40 to 50 years old. Stomach and intestinal cancers were more common in men and endometrial cancers in women. It is very common for both parents and children to have cancer. Among 95 cancer patients in the offspring, 72 (76%) of them have one parent who has also suffered from cancer. 7.Application of PET/CT in tumor diseases Malignant tumor is one of the major diseases that endanger human health and cause human death, and there are more than 1.6 million new cancer patients in China every year, and the number of people suffering from cancer is increasing year by year. The occurrence and development of malignant tumors often start from the change of proto-oncogene, and then go through metabolic abnormalities, functional abnormalities, anatomical abnormalities, and finally clinical symptoms appear. PET/CT has unique advantages in the early, qualitative and localized diagnosis of tumors, which is an indispensable tool for early diagnosis and scientific and effective treatment. ◆PET/CT, if used as a health checkup, can detect hidden early tumor lesions and make them curable. ◆For clinical suspicion of tumor lesions, PET/CT can make differential diagnosis and distinguish benign and malignant lesions. For patients with confirmed malignant tumors, PET/CT can accurately detect metastatic lesions throughout the body and guide the treatment plan. For patients with clinically detected metastases but unknown primary tumor foci, PET/CT can help detect the primary tumor foci. For patients with confirmed malignant tumors, PET/CT can detect residual lesions after surgery, radiotherapy or chemotherapy, monitor the efficacy of treatment, and adjust the treatment plan at the right time. ◆For confirmed malignant tumor lesions, PET/CT can precisely spatially localize, implement and optimize radiotherapy (e.g. χ, γ-knife) plans. ◆For scar, residual or recurrent foci after tumor treatment, PET/CT can effectively identify them.