Factors that cause most neoplasms are unknown. They can be classified as environmental factors (e.g., chemical and radiation), host factors and disease associations, and viruses.

Environmental Factors

The incidence of cancer has been correlated with certain environmental factors. Table 1 lists environmental factors that have been definitively linked with cancer, including aerosol and industrial pollutants, drugs, and infectious agents. Radiation exposure is also known to be associated with specific types of cancer (e.g., acute leukemia, thyroid cancer, sarcomas, breast cancer). Women concerned about organochlorine substances (e.g., polychlorinated biphenyls [PCBs], dioxins, pesticides [DDT, banned in 1972]) can be reassured that available evidence does not suggest an association between exposure to these chemicals and breast cancer.

Table1. Selected Environmental Factors Associated With Cancer

Most chemical carcinogens are inactive in their native state and must be activated by enzymes in the cytochrome P-450 or other enzyme systems (e.g., bacterial enzymes or enzymes induced by alcohol).

In radiation carcinogenesis, ionizing particles (e.g., alpha and beta particles, gamma rays, x-rays) hydrolyze water into free radicals, which are mutagenic to DNA by activating protooncogenes. Ultraviolet (UV) light, especially UVB, induces the formation of thymidine dimers, which distort the DNA molecule, leading to skin cancers (e.g., basal cell carcinoma, malignant melanoma).

Host Factors and Disease Associations

Various host factors have been linked to a higher than expected incidence of cancer. For example, the presence of certain genetic disorders (e.g., Down syndrome) is associated with an increased incidence of leukemia. The link between certain genetic abnormalities and leukemia is consistent with a germinal or somatic mutation in a stem cell line.

Familial clustering of germ cell tumors, malignant tumors arising in the testis, has been observed, particularly among sib lings. Cryptorchidism and Klinefelter’s syndrome are predisposing factors in the development of germ cell tumors arising from the testis and mediastinum, respectively.

The incidence of cancer is 10,000 times greater than expected in patients with an immunodeficiency syndrome. The increased incidence of lymphomas in congenital, acquired, and drug-induced immunosuppression is consistent with the failure of normal immune mechanisms or antigen overstimulation with a loss of normal feedback control. Table 2 lists other cancer-related conditions.

Table2. Cancer-Related Conditions

Viruses

Viral causes of some cancers are known. Viruses associated with specific cancers are listed in Table 1. Nonpermissive cells that prevent an oncogenic RNA or DNA virus from completing its replication cycle often produce changes in the genome that result in the activation of proto-oncogenes or inactivation of suppressor genes.

اخر الاخبار

اخبار العتبة العباسية المقدسة

المجمع العلمي يواصل إقامة مسابقة الثقلين القرآنية لطلبة مدارس كربلاء

عضو مجلس إدارة العتبة العباسية المقدسة يطلع على آليات تطوير البرامج التعليمية في مجموعة العميد

مجموعة مناحل الكفيل تختتم مشاركتها في معرض السليمانية الدولي للزراعة والصناعات الغذائية

لتوثيق التراث العلمي.. وفد قسم شؤون المعارف يلتقي عددًا من أعلام مدينة النجف

المزيد

الآخبار الصحية

ثورة طبية.. الذكاء الاصطناعي يكشف سرطان الكلى في وقت قياسي

لتعزيز الطاقة والتغلب على التعب.. عليك بـ7 طرق بسيطة

لتحسين الهضم والتحكم في الشهية.. ما أفضل وقت لتناول التمر؟

خبراء يكشفون تأثير الاستحمام في الظلام على جودة النوم !

المزيد

الآخبار التكنلوجية

إزالة ثاني أكسيد الكربون من الغلاف الجوي.. ما دور المحيطات والبحار؟

نظائر الهيليوم مقياس لاكتشاف رواسب الذهب.. كيف ذلك؟

الصين تطلق أول ناقلة نفط خام ذكية في العالم تعمل بالميثانول

الزمن على المريخ أسرع من الأرض.. دراسة علمية تكشف الفوارق

المزيد

مواضيع ذات صلة

Application of Liquid Biopsy to Non-small- Cell Lung Cancer Lung

Circulating Tumor DNA

Biomarkers in the Blood and in Tissues: A Complementary Approach

Biomarkers in Oncology: An Evolving Concept

Clinical Development of Venetoclax for Acute Myeloid Leukemia

Clinical Development of Oblimersen for Acute Myeloid Leukemia

Modalities for treating cancer

Tumor markers

Proto-oncogenes

Cancer-Predisposing Genes

Stages of Carcinogenesis

Types of Tumors