What Is Cancer Etiology?

In medicine, cancer refers to malignant tumors that originate from epithelial tissues, and is the most common type of malignant tumors. Correspondingly, malignant tumors originating from mesenchymal tissue are collectively called sarcomas. A few malignant tumors are not named according to the above principles, such as nephroblastoma and malignant teratoma. Generally speaking, "cancer" generally refers to all malignant tumors. Cancer has biological characteristics such as abnormal cell differentiation and proliferation, uncontrolled growth, invasion, and metastasis. Its occurrence is a multi-factor, multi-step complex process, which is divided into three processes: carcinogenesis, cancer promotion, and evolution. Infection, occupational exposure, environmental pollution, unreasonable diet, and genetic factors are closely related.

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    Basic Information

    English name
    cancer
    Visiting department
    Oncology
    Multiple groups
    Irregular life, smoker, drinker
    Common causes
    Not fully understood
    Common symptoms
    Local symptoms such as lump, pain, ulcer, bleeding, obstruction

    Causes of cancer

    The cause of malignant tumors is not fully understood. The factors that are more clearly related to cancer can be divided into two categories: exogenous and endogenous:
    Exogenous factor
    (1) Living habits Bad living habits such as smoking are closely related to the occurrence of cancer. About one-third of patients who die from cancer are related to smoking, and smoking is a major risk factor for lung cancer. Ingestion of large amounts of strong alcohol can lead to the occurrence of oral, throat, and esophageal malignancies. High-energy high-fat foods can increase the incidence of breast cancer, endometrial cancer, prostate cancer, and colon cancer. Drinking contaminated water and eating mildew food can induce liver cancer, esophageal cancer, and gastric cancer.
    (2) Environmental pollution and occupational pollution of air, drinking water and food can cause serious harm to human beings. The World Health Organization has published environmentally-related carcinogens including: arsenic, asbestos, benzidine, 4-aminobiphenyl, chromium, estradiol, radioactive tritium, coal tar, mineral oil, estrogen coupling, etc. . These chemical or physical carcinogens in the environment enter the body through the body's surface, breathing, and digestive tract, causing cancer.
    (3) Natural and biological factors Natural factors can also cause cancer, for example, ultraviolet rays can cause skin cancer under certain conditions. Biological factors are mainly viruses, of which 1/3 are DNA viruses and 2/3 are RNA viruses. DNA viruses such as Epstein-Barr virus are associated with nasopharyngeal carcinoma and Burkitt lymphoma, human papillomavirus infection is associated with cervical cancer, and hepatitis B virus is associated with liver cancer. RNA viruses such as T-cell leukemia / lymphoma virus are associated with T-cell leukemia / lymphoma. In addition, bacteria, parasites, and fungi can cause cancer under certain conditions. For example, Helicobacter pylori infection is related to the occurrence of gastric cancer. Schistosomiasis in Egypt has been proven to induce bladder cancer. Aspergillus flavus and its toxins can cause liver cancer.
    (4) Chronic irritation and trauma Traumatic and local chronic irritation such as burns, deep scars and chronic skin ulcers can all become cancerous.
    (5) Iatrogenic factors such as ionizing radiation, such as X-rays, radionuclides, can cause skin cancer, leukemia, etc .; cytotoxic drugs, hormones, arsenic agents, immunosuppressants, etc. are all carcinogenic.
    2. Endogenous factors
    (1) Genetic factors The truly directly inherited tumors are only a few uncommon tumors. The role of genetic factors in the development of most tumors is to increase the body's tendency to develop tumors and susceptibility to oncogenic factors, the so-called genetic susceptibility. , Including chromosomal instability, genetic instability, and microsatellite instability. For example, those with familial colonic adenoma polyps, because of the presence of APC gene mutations in germline cells, most have colon cancer after age 40; Brca-1 and Brca-2 mutations are associated with the occurrence of breast cancer, with an incidence rate of more than 80%.
    (2) Immune factors Congenital or acquired immune deficiency is prone to malignant tumors. For example, patients with gamma protein deficiency are susceptible to leukemia and lymphoid hematopoietic tumors. The incidence of malignant tumors in AIDS (AIDS) patients is significantly increased. However, most malignant tumors occur in people with "normal" immune function. The main reason is that tumors can escape the surveillance of the immune system and destroy the immune system. The mechanism is not completely clear.
    (3) Endocrine factors Abnormal hormone levels in the body are one of the tumor-causing factors, such as estrogen and prolactin are related to breast cancer, and growth hormone can stimulate the development of cancer.

    Clinical manifestations of cancer

    The clinical manifestations of malignant tumors vary depending on the organ, location and degree of development, but malignant tumors often have no obvious symptoms in the early stage, and often have no specificity even if they are symptomatic. When patients have specific symptoms, the tumor often belongs to Late. The clinical manifestations of cancer are generally divided into two aspects: local manifestations and systemic symptoms.
    Local manifestations of cancer
    (1) Mass A malignant proliferation of cancer cells can be touched on the body surface or deep with your hands. Thyroid, parotid, or breast cancer can be touched shallowly under the skin. Tumor metastasis to lymph nodes can cause lymph node enlargement, and some superficial lymph nodes, such as neck lymph nodes and axillary lymph nodes, are easily touched. As for gastric cancer and pancreatic cancer in the deep parts of the body, they can only be touched by pressing hard.
    (2) Pain Swelling or ulceration of the tumor, infection, etc. can cause peripheral nerves or nerve trunks to be stimulated or compressed, and local pain may occur. The appearance of pain often indicates that the cancer has entered the middle and advanced stages. At first, it is mostly dull or dull, which is obvious at night. It gradually increased and became intolerable later, day and night, especially at night. Analgesics are generally ineffective.
    (3) Ulcers Tumors on the body surface or gastrointestinal tract, if they grow too fast, can cause tissue necrosis due to insufficient blood supply or ulceration due to secondary infection. For example, some breast cancers can have crater-like or cauliflower-like ulcers in the breast, secrete bloody secretions, and have a foul odor when they are infected.
    (4) Bleeding The cancer tissue invades blood vessels or the small blood vessels of the cancer tissue rupture. Such as lung cancer patients can have hemoptysis or blood in sputum; gastric cancer, esophageal cancer, colon cancer can vomit blood or blood in the stool, urinary tract tumors can appear hematuria, cervical cancer can have vaginal bleeding, liver cancer rupture can cause intra-abdominal bleeding.
    (5) Obstruction Obstruction of cavity organs caused by rapid growth of cancer tissue. Dyspnea and atelectasis can occur when the obstruction is in the respiratory tract; esophageal cancer obstructs esophagus and swallows difficult; biliary tract cancer can block the common bile duct and cause jaundice; bladder cancer blocks the urethra and dysuria; etc. gastric cancer with pyloric obstruction Causes epigastric fullness and vomiting after a meal.
    (6) Other intracranial tumors can cause a variety of neurological symptoms such as visual impairment (oppression of the optic nerve), facial paralysis (oppression of the facial nerve); bone tumors invading the bone can cause fractures; liver cancer caused by a decrease in plasma albumin and ascites. Corresponding symptoms can occur in tumor metastasis, such as regional lymphadenopathy, and cancerous pleural effusion caused by lung cancer pleural metastasis.
    2. Systemic symptoms
    Most of the early malignant tumors have no obvious systemic symptoms. Some patients may have non-specific symptoms such as weight loss, loss of appetite, cachexia, excessive sweating (night sweats at night), anemia, and fatigue. In addition, about 10% to 20% of tumor patients will develop systemic and systemic symptoms that are not related to metastasis and consumption before or during the onset of the disease, which is called para-tumor syndrome. Manifestations include tumor fever, cachexia, hypercalcemia, abnormal antidiuretic hormone secretion syndrome, and carcinoid syndrome.
    3. Tumor metastasis
    Cancer cells can metastasize to nearby and distant tissues and organs by direct spreading, lymphatic, hematological, and implantation. The direct spread is caused by the invasive growth of cancer cells, which is continuous with the primary lesion, such as rectal cancer and cervical cancer invading the pelvic wall; Lymphatic metastasis is mostly regional lymph node metastasis, but skipped non-regional lymph nodes may also occur And metastasis to the distant place; hematogenous metastasis of tumor cells through the systemic circulatory venous system, portal vein system, paravertebral venous system and other tissues and organs; implantation metastasis is tumor cells in the body cavity or cavity organs Metastases are most commonly implanted into the pelvic cavity for gastric cancer.

    Cancer screening

    Tumor marker
    Although tumor markers lack specificity, they still have some value in assisting diagnosis and judging prognosis. Mainly include enzymatic examination, such as alkaline phosphatase, which can be significantly increased in patients with liver cancer and osteosarcoma; glycoproteins, such as lung cancer serum acid glycoprotein, can be increased, digestive system tumor CA19-9, etc .; tumor-associated antigens For example, carcinoembryonic antigen (CEA) may increase in gastrointestinal tumors, lung cancer, breast cancer, and alpha-fetoprotein (AFP) may increase in liver cancer and malignant teratoma.
    2. Genetic testing
    Including the detection of gene expression products, gene amplification detection and gene mutation detection, can determine the presence of specific genes in tumors or cancers to make a diagnosis.
    3. Imaging examination
    (1) X-ray examination Including fluoroscopy and plain radiographs, such as certain peripheral lung cancer and bone tumors, specific shadows can appear on plain radiographs; radiographic examinations, such as upper gastrointestinal radiography, may find esophageal and gastric cancer, and barium enema can show colon cancer Etc .; special X-ray imaging, such as molybdenum photography, is used for breast cancer examination.
    (2) Ultrasound is simple and non-invasive. It is widely used in liver, gallbladder, pancreas, spleen, kidney, thyroid, breast and other parts. Ultrasound-guided biopsy of the tumor can be performed with high success rate.
    (3) Computed tomography (CT) examination is often used for the diagnosis and differential diagnosis of intracranial tumors, parenchymal organ tumors, parenchymal masses and lymph nodes. CT examination has high resolution and clear imaging, and early tumors of certain specific organs can be found without symptoms. Low-dose spiral CT can reduce the radiation dose to the human body, and the sharpness of the image can meet the clinical needs, so that large-scale screening of high-risk populations of tumors in specific parts can be achieved, such as early screening of lung cancer, which has been achieved With good results.
    (4) Radionuclide imaging According to the different uptake of different elements by different tumors, different radionuclides are used to image the tumors. The positive rate of bone tumor diagnosis is high, and it can also be used to display thyroid tumors, liver tumors, and brain tumors.
    (5) Compared with CT, magnetic resonance (MRI) has better contrast resolution, no bone artifact interference, and can display any cross section, which is the first method to check the central nervous system and spinal tumors. It is also valuable for observing the relationship between tumors and blood vessels, mediastinal tumors and enlarged lymph nodes, and pelvic tumors.
    (6) Positron emission tomography (PET) uses positron nuclides as tracers. The gamma photons generated by positrons are used to reconstruct a tomographic image of the tracer in the body. Imaging technology has a high accuracy in the qualitative diagnosis of solid tumors and the examination of metastases.
    4. Endoscopy
    It is the application of endoscopic and endoscopic techniques to directly observe tumors or other lesions in cavity organs and body cavities, and can take tissue or cells for histopathological diagnosis. Commonly used are gastroscopy, bronchoscopy, colonoscopy, proctoscope, laparoscopy , Thoracoscope, hysteroscope, colposcopy, cystoscope, ureteroscope, etc.
    5. Pathological examination
    Pathological examination is currently a means of confirmatory diagnosis.
    (1) Clinical cytology examination Including cytological examination of natural exfoliated cells such as sputum, urine sediment, pleural effusion, peritoneal effusion, and vaginal smear; mucosal cell examination, such as esophageal mesh, stomach Mucosal eluate, cervical scraping, and brushing of cells on the surface of the tumor under endoscope; fine-needle aspiration cell examination, such as aspirating tumor cells with a needle and a syringe for smear staining. Cytological examination is simple and widely used, but in most cases, only qualitative cytological diagnosis can be made, and sometimes the diagnosis is difficult.
    (2) Histopathological examination According to the different parts, size, and nature of the tumor, different methods of taking materials were taken. Superficial tumors of the cavity organ mucosa are often obtained for pathological examination during endoscopic examination; puncture biopsy should be performed for tumors located in the deep or large and complete surface; partial tumor tissues are removed for rapid pathological examination during surgery . Pigmented nodules or moles are generally not excised or biopsied, and they should be completely removed. Various biopsies have the potential to promote the spread of malignant tumors and need to be performed shortly before or during surgery.

    Cancer diagnosis

    According to the different parts and properties of the tumor, comprehensive analysis of the clinical manifestations and signs of patients, combined with laboratory examinations and imaging, cytopathological examinations can usually make a clear diagnosis. In addition to clarifying the presence or absence of malignant tumors, their scope and extent should be further understood in order to formulate treatment plans and assess prognosis. However, there is still no ideal specific early diagnosis method, especially for the early diagnosis of deep tumors.

    Cancer staging

    The staging of malignant tumors helps to rationally formulate treatment plans, correctly evaluate efficacy and judge treatment prognosis. The TNM staging method proposed by the International Anti-Cancer Alliance is a widely used staging method. In the TNM staging system, T is the primary tumor, N is the lymph node, and M is the distant metastasis.
    T stage (Tumor) represents the degree of tumor development can be divided:
    T X cannot find the primary tumor or define the stage;
    T 0 has no primary tumor;
    Tis carcinoma in situ;
    T 1 -T 4 according to tumor size and growth and spread;
    N stage (LymphNode) indicates that according to the impact of lymph nodes:
    N X cannot determine the stage of lymph node impact;
    N 0 cancer cells without local lymph node metastasis;
    N 1 -N 3 lymph node metastasis;
    M staging (Migration) is divided into:
    M X cannot determine the stage of distant metastasis;
    No remote transfer occurred at M 0 ;
    M 1 has generated a remote transfer;
    Different T, N, and M combinations are diagnosed at different stages, and the TNM staging criteria for various tumors are agreed by professional conferences.
    The treatment and prognosis of some tumors are related to pathological grade or depth of invasion, so other staging methods can also be used.

    Cancer treatment

    There are many types of malignant tumors, with different types of properties, different tissues and organs involved, different stages of disease, and different responses to various treatments. Therefore, most patients need comprehensive treatment. The so-called comprehensive treatment refers to the comprehensive use of surgery, chemotherapy, radiotherapy, immunotherapy, traditional Chinese medicine treatment, interventional treatment, microwave treatment and other means according to the patient's physical condition, the pathological type of the tumor, and the scope of the invasion. Rates and improve the quality of life of patients.
    Surgical treatment
    In theory, cancer can be cured if the tumor cells are completely removed by surgery. For early or early solid tumors, surgical resection is still the preferred treatment. According to the purpose of surgery, it can be divided into the following types:
    (1) Radical surgery Because the malignant tumor grows fast and there is no envelope on the surface, it has no obvious boundary with the surrounding normal tissues, local infiltration is obvious, and it can be metastasized through lymphatic vessels. Therefore, surgery should completely remove the tumor and a certain range of normal tissues and lymph nodes that may be affected. This surgery is suitable for patients with limited tumor range, no distant metastasis, and good constitution. According to the scope of resection, it is divided into tumor resection, extensive resection, radical surgery and enlarged radical surgery.
    (2) Palliative surgery The tumor has a wide range, and advanced patients who have metastasized and cannot undergo radical surgery. In order to reduce pain, maintain nutrition and prolong life, you can only remove some tumors or perform surgery to reduce symptoms, such as fistula Surgery, short circuit of digestive tract and other operations. Advanced tumors can be used for major resection of tumors to reduce tumor burden and lay the foundation for future radiotherapy, chemotherapy or other treatments. Such as advanced ovarian cancer can palliative resection of most ovarian tumors, two operations after chemotherapy, removal of residual lesions, can significantly extend the survival of patients.
    (3) Diagnostic Surgery Specimens for pathological examination of tumors are obtained through different surgical methods, such as puncture and material extraction or small pieces of tissue cut during the operation. For deep visceral masses, open chest, laparotomy, or craniotomy examinations are required. After the intraoperative pathological examination is confirmed, the surgical operation is performed immediately.
    (4) Preventive surgery Used for precancerous lesions to prevent it from developing malignant or developing advanced cancer. For example, patients with familial colonic polyposis can benefit from prophylactic colectomy because such patients do not remove the colon. About half can develop colon cancer after the age of 40, and almost 100% can develop colon cancer after the age of 70. Cervical conical resection can be performed when the cervical dysplasia is severe to prevent the occurrence of cervical cancer. BRCA1 and BRCA2 have mutations in hereditary breast cancer family members that can be used for preventive resection of both breasts.
    (5) Surgery for metastatic foci. For a single metastatic foci such as lung, liver, bone, etc., resection treatment can still strive for 5-year survival rate. If the primary lung cancer has only a single metastatic lesion of the bone, and the primary lung cancer can be completely resected, the resection of the primary and metastatic lesions can be performed simultaneously or successively.
    2. Chemotherapy
    Cancer is treated with drugs that kill cancer cells. Because the biggest difference between cancer cells and normal cells is the rapid cell division and growth, the principle of anticancer drugs is to inhibit the growth of cancer cells by interfering with the mechanism of cell division, such as inhibiting DNA replication or preventing chromosome separation. . Most chemotherapeutic drugs are not specific, so they will kill normal tissue cells that undergo cell division at the same time, so they often hurt healthy tissues that need to be divided to maintain normal functions, such as intestinal mucosal cells. However, these tissues usually repair themselves after chemotherapy. Because some drugs can be used in combination for better results, chemotherapy often uses two or more drugs at the same time, which is called "combined chemotherapy". Most patients receive chemotherapy in this way.
    3. Radiotherapy
    Also called radiation therapy and radiation therapy, it uses radiation to kill cancer cells and shrink tumors. Radiation therapy can be via external radiation therapy or in vivo approach radiation therapy. Because cancer cells grow and divide faster than normal cells, by destroying the cell's genetic material by radiation, it can prevent the cells from growing or dividing, and then control the growth of cancer cells. However, the effect of radiation therapy can only be limited to the area under irradiation. The goal of radiation therapy is to destroy all cancer cells as much as possible, while minimizing the impact on nearby healthy tissue. Although radiation can cause damage to both cancer cells and normal cells, most normal cells can recover from the damage of radiation therapy.
    4. Targeted therapy
    Targeted therapy has been effective in treating certain types of cancer since the late 1990s. It can treat cancer as effectively as chemotherapy, but the side effects are much reduced compared with chemotherapy. It is also a very active research area at present. The principle of this treatment is to use small molecules with abnormal or dysregulated proteins that specifically fight cancer cells, such as tyrosine phosphatase inhibitors, to treat non-small cell lung cancer with EGFR (epidermal growth factor receptor) sensitive mutations. The effect is significant, but the emergence of drug-resistant genes is currently the main obstacle to further improve the effect.
    5. Immunotherapy
    Immunotherapy uses immune mechanisms in the human body to fight tumor cells. There are already many immunotherapies under study to fight cancer. At present, cancer vaccine therapy and monoclonal antibody therapy are more advanced, and immune cell therapy is the latest development of treatment technology in recent years.
    6. Traditional Chinese Medicine and Chinese Medicine Treatment
    Cooperating with surgery and radiotherapy and chemotherapy can reduce the toxic and side effects of radiotherapy and chemotherapy, promote patient recovery and enhance tolerance to radiotherapy and chemotherapy.
    7. Gene therapy
    Through the method of introducing foreign genes into the human body to correct gene defects, the concept of gene therapy for malignant tumors has been expanded from correcting genetic defects to introducing foreign genes into the human body, and finally achieves direct or indirect suppression or killing of tumor cells.
    8. Endocrine therapy
    The occurrence and growth of certain tumors are closely related to hormones in the body, so they can be treated by changing the endocrine condition. For example, sex hormones can be used for palliative treatment of breast cancer, prostate cancer, and endometrial cancer.
    9. High temperature treatment
    The microwave hyperthermia technology, ultrasonic focusing and radio frequency technology developed in the past 10 years or more have used local high temperature to cause cancer cells to be necrotic, and less damage normal tissues, which is simple and safe.
    10. Laser treatment
    Using the advantages of high density of laser, good parallelism, accurate positioning, etc., hematoma can be performed after moderate focus.
    11. Cryotherapy
    When frozen, ice crystals form inside and outside the cell, causing cancer cell damage. Can be used for surface tumors or visceral tumors.

    Cancer prevention

    The International Alliance against Cancer believes that one third of cancers can be prevented, one third of cancers can be cured if diagnosed early, and one third of cancers can reduce pain and prolong life. Based on this, the concept of tertiary prevention of malignant tumors is proposed:
    Primary prevention is to eliminate or reduce the factors that may cause cancer and prevent the occurrence of cancer. About 80% of cancers are related to the environment and lifestyle. Improving lifestyles, such as quitting smoking, restricting alcohol consumption, diversifying foods, eating less preserved foods, controlling weight, exercising appropriately, paying attention to environmental protection, identifying carcinogens and cancer-promoting agents in the environment, and strengthening occupational protection are all important prevention measures. Cancer measures. In recent years, both immunoprevention and chemoprevention belong to primary prevention, such as large-scale vaccination of hepatitis B vaccine and selective cyclooxygenase 2 (COX-2) inhibitors for chemoprevention of colorectal adenomas.
    Secondary prevention refers to how to detect and treat cancer at an early stage once it occurs. Including: recognition and attention to cancer danger signals (such as persistent indigestion, vaginal bleeding after menopause, changes in bowel habits, long-lasting ulcers, etc.); regular inspection of high-incidence areas and high-risk groups; Timely treatment; strengthen the monitoring of susceptible people; tumor self-examination (regular self-examination of exposed parts of the body).
    Tertiary prevention is rehabilitation after treatment, preventing deterioration of the condition, improving quality of life, alleviating pain, and prolonging life.

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