Environmental factors influence the development of cancerous tumors.
Development of cancerous tumors
Viruses are involved in the pathogenesis of human malignant tumors. This can occur through the integration of individual sections of the viral genome into the host DNA. These new genes are expressed in the body and can disrupt cell growth, cell division, or destroy the normal host genes necessary to control cell growth and division. In addition, a viral infection can cause dysfunction of the immune system, leading to impaired immune surveillance of the early stages of tumor growth.
Some types of parasites can contribute to the development of cancer. So, Opist-horchis sinensis is associated with carcinoma of the pancreas and bile ducts.
Chemical carcinogens can induce gene mutations and cause uncontrolled growth and tumor formation. Other substances, called co-carcinogens, have a small or total absence of carcinogenic activity, but they enhance the carcinogenic effect of other agents with simultaneous exposure.
Ultraviolet radiation can induce skin cancer (for example, basal and scaly cell carcinoma, melanoma), damaging DNA. DNA damage lies in the formation of thymidine dimers, which may not recover with congenital disorders of DNA repair mechanisms [for example, xeroderma pigmentosum] or by more rare events.
Ionizing radiation has a carcinogenic effect. For example, survivors of the atomic blasts in Hiroshima and Nagasaki have a higher incidence of leukemias and other malignant diseases. The use of X-ray treatment of non-malignant diseases (ak-not, an increase in thymus or adenoids, ankylosing spondylitis) causes an increase in the incidence of such diseases as acute and chronic leukemia, Hodgkin's lymphoma and non-Hodgkin's lymphomas, multiple myeloma, aplastic anemia, myelofibrosis, melanoma and cancer thyroid gland.
Medical professionals who have contact with anti-neoplastic drugs also have a risk of adverse effects on the reproductive system causing lung cancer to develop after a 15–20 year latency period.Long-term occupational exposure to radiation or deposition of thorium dioxide in the body predisposes to the development of angiosarcoma and acute non-lymphoblast leukemia.
Chronic exposure of the skin leads to the development of chronic dermatitis and, more rarely, scaly-cellular carcinoma. These events are mainly due to rare mutations that occur more frequently due to acceleration of the cell cycle.
Dysfunction of the immune system as a result of genetic mutations that have arisen in the course of acquired diseases, with age or with immunosuppressive therapy disrupts immunological surveillance of early stages of tumor development and leads to an increased risk of cancer. Known onco-associated immune diseases, such as ataxia-telangiectasia [acute lymphoblastic leukemia (ALL), brain tumors, stomach cancer]; Whiskott-Aldrich syndrome (lymphoma, ALL); X-linked agamma-globulinemia (lymphoma, ALL); secondary immunodeficiency that occurs when taking immunosuppressants or HIV infection (lymphoma, Kaposi's sarcoma); rheumatological diseases such as SLE, RA, Sjogren syndrome (B-cell lymphoma); common immune diseases (lymphoreticular neoplasia).