Cancer, its types and causes

  • Cancer (usually symbolized by a crab) is a non-communicable disease.
  • Cancer is the unregulated and uncontrolled proliferation of cells or it is a breakdown of the regulating mechanism that governs normal cell division.
  • The study of cancer is called oncology.
  • The tumor (a mass of tissue of abnormal cells)or neoplasm formed by uncontrolled cell division can be of two types:
    1. Benign tumors:
      • They are localized tumors and are bound within a connective tissue coating.
      • They don’t spread over the surrounding tissues.
      • They are not fatal or harmful. E.g. moles and warts
    2. Malignant tumors:
      • They are cancerous and harmful and spread into the surrounding tissues by two means: invasion and metastasis.
      • Invasion is the penetration of the cells of malignant tumor into the neighboring tissue where they from invasion tumors.
      • Metastasis is the penetration of cancerous cell into the blood capillaries from where they are carried to different parts of the body.

Types of cancer:

  • Based on the types of tissues affected, cancer is of following types:
  1. Carcinoma:
    • It is the cancer of the epithelial lining, which can be ectodermal, mesodermal or endodermal in origin.
    • This type of cancer can develop in the gut lining, glands (exocrine or endocrine) or skin etc.
    • About 80% of the cancers are carcinomas.
    • g. lung cancer, breast cancer, duodenal cancer, colon cancer, skin cancer, cervix cancer etc.
  2. Sarcoma:
    • It is the cancer of connective tissues or muscles, and is mesodermal in origin.
    • Only 1-2% of cancers are of this type.
    • g. cancer of bones and cartilages etc.
  3. Leukemia:
    • It is the cancer of blood particularly of granulocytes (WBCs) and hence is also called granulocytic leukemia.
    • It is a specific abnormality in chromosome 22 (Philadelphia chromosome) of leukemia cancer cells (particularly chronic myeloid leukemia (CML) cells).
  4. Lymphoma:
    • It is the cancer of lymphatic tissues or lymphocytes present in the lymph.
    • The most common lymphoma is Hodgkin’s disease.
  5. Mixed types of cancer:
    • Lipoma: it is the cancer of adipose tissue subcutaneous fats (beneath the skin).
    • Melanoma:  the cancer of melanocytes present in skin.
    • Teratoma: it is the cancer of embryonic or fetal tissue that is a tumor-like embryo or embryo-like tumor formed by the heterogeneous mixture of tissues.
    • Myeloma:  the cancer of bone marrow.
    • Myoma:  the caner of muscles.

Causes of cancer:

  • The cancer causing agents or factors are called carcinogens.
  • Carcinogens may be physical, chemical or biological factors.
    1. Physical agents (Radiations):
      • UV rays, ϒ-rays (gamma rays), infra-red rays or X-rays can cause gene mutation and produce oncogenic transformation.
      • The radiation from nuclear bombs and leakage from nuclear reactors can also cause mutation.
    2. Chemical agents:
      • Certain chemicals may cause cancer e.g. n-nitroso-dimethylene (in cigarette smoke) and asbestos dust causing lung cancer.
      • Cadmium oxide causing cancer of prostate gland, PVC (polyvinyl chloride) and Aflatoxin (from fungus Aspergillus) causing liver cancer.
      • Nitrosamine causing colon cancer, diethylstilbestrol causing vaginal cancer.
    3. Biological agents (viruses):
      • Viruses don’t cause cancer as pathogens but alter DNA sequence which produces abnormal proteins.
      • Such viruses are called oncoviruses.

Carcinogens can also be categorized on the basis of their mode of action as:

  • DNA transformers: these agents can cause alteration in DNA that leads to cancer.
  • Tumor promoters: these agents (e.g. growth factors or hormones) promote the proliferation of cells which have already undergone genetic alteration.
  • Tumor viruses: such viruses are capable of making oncogenic transformations

Cancer, its types and causes