Cancer : Definition, Types and Fuction - Practice Questions & MCQ

• Cancer is an abnormal and uncontrolled division of cells, known as cancer cells that invade and destroy the surrounding tissues.
• In our body, cell growth and differentiation are highly controlled and regulated. 
• In cancer cells, there is a breakdown of these regulatory mechanisms. 
• Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth.
• Cancer cells appear to have lost this property. 
• As a result of this, cancerous cells just continue to divide giving rise to masses of cells called tumors.

Types of Tumours:

• Benign Tumour (= Non-malignant Tumour):
  • It remains confined to the site of its origin and does not spread to other parts of the body. 
  • It causes limited damage to the body. It is non-cancerous.
• Malignant Tumour (= Cancerous Tumour):
  • The malignant tumors, on the other hand are a mass of proliferating cells called neoplastic or tumor cells. 
  • These cells grow very rapidly, invading and damaging the surrounding normal tissues. 
  • As these cells actively divide and grow they also starve the normal cells by competing for vital nutrients. 
  • Cells sloughed from such tumors reach distant sites through blood, and wherever they get lodged in the body, they start a new tumor there. 
  • This property called metastasis is the most feared property of malignant tumors.

Types of Cancers:

• Carcinomas:
  • This type is mainly derived from epithelial cells. 
  • They include cervical (cervix is part of uterus) cancer, breast cancer, skin cancer, brain cancer, lung cancer, stomach cancer, etc. 
  • About 80% of all tumors are carcinomas.
• Sarcomas:
  • These cancers are located in connective and muscular tissues derived from mesoderm. 
  • Thus, they include the cancers of bones, cartilages, tendons, adipose tissue, lymphoid tissue and muscles.
• Leukemia:
  • These are characterized by an abnormal increase of white blood corpuscles count due to their increased formation in the bone marrow. 
  • Leukemia are commonly called blood cancers.
     

Causes of cancer:

• Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents.
• These agents are called carcinogens. 
• Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV cause DNA damage leading to neoplastic transformation. 
• The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.
• Cancer-causing viruses called oncogenic viruses have genes called viral oncogenes. Furthermore, several genes called cellular oncogenes (c-onc) or proto-oncogenes have been identified in normal cells which, when activated under certain conditions, could lead to oncogenic transformation of the cells.

Cancer detection and diagnosis:

• Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias. 
• In a biopsy, a piece of the suspected tissue cut into thin sections is stained and examined under microscope (histopathological studies) by a pathologist. 
• Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs.
• Computed tomography uses X-rays to generate a three-dimensional image of the internals of an object. 
• MRI uses strong magnetic fields and non-ionizing radiations to accurately detect pathological and physiological changes in the living tissue.
• Antibodies against cancer-specific antigens are also used for detection of certain cancers. 

Treatment of cancer:

• The common approaches for the treatment of cancer are surgery, radiation therapy and immunotherapy. 
• In radiotherapy, tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass. 
• Several chemotherapeutic drugs are used to kill cancerous cells. 
• Some of these are specific for particular tumors. Majority of drugs have side effects like hair loss, anemia, etc. 
• Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy.
• Tumor cells have been shown to avoid detection and destruction by the immune system.
• Therefore, the patients are given substances called biological response modifiers such as ã-interferon which activate their immune system and help in destroying the tumor.