EXTERNAL FACTOR AS A "CAUSE OF CANCER"

      Research on the role of External Factors as a cause of Cancer indicate the neither the Environment in general non Pollution in particular is responsible for a large fraction of Cancer Cases .

 

   Rather ,DIET ,TOBACCO and other agents including medical and dental X- Rays ,as well as all drugs ,play significant roles in Cancer devlopment .

    It's estimated that these agents causes 50 percent of all Cancer Causes .Thus Personal Choices (the Composition of Food in the Diet ,Tobacco use) figure prominently in the Cancer Equation .Education and Judicious changes in Lifestyles could prevent a high percentage of all Human Cancers .

'HEPATITIS B' AND CANCER

    Epidemiological Survey show that Individuals who devlop a form of Liver cancer known as Hepato-cellular carcinoma (HCC) are infected with the Hepatitis B Virus (HBV) .

    In-fact ,for those carrying HBV ,the risk of Cancer increases by a factor of 100 .

    It's Most prevalent in Asia , and tropical region of Africa .

    

  The infection produces a wide range of responses ,from chronic ,Self - limiting infections with few Symptoms ,to active hepatitis and Cirrhosis , to total Liver disorders and Hepato-cellular carcinoma .

    In the last few years ,efforts have centered on understanding the mechanism by which HBV replicates and it's role in causing Liver Cancer .

   The possible outcomes following cellular infection with Hepatitis B virus (HBV) .Following the Integration of the Viral Chromosome into the Human genome .Oncogenes can be activated resulting in Tumor Formation .Integration of the HBV genome can also cause Chromosome Instability .
   Including the production of trans-locations and deletions the trigger a malignant cyclin Agene ,triggering abnormal regulation of the cell cycle and cellular proliferation ,resulting cancer Formation .

'FAP' AND COLON CANCER

In the 'FAP' Associated Model , spontaneous cases of 'Colon Cancer' begin with a Mutation in the APC gene. Which maps to the long arm of chromosome 5 .

 This mutation occurs in a normal epithelial cell in the living of the colon ,In spontaneous causes ,an APC Mutation causes epithelial cells to partially escape cell cycle control .These cells divide to form a small cluster called polyp .those who inherit a mutant APC allele have the mutation in all cells of their body .As a result , APC Hetero Zygotes from hundreds or thousand of polyps .

   In either case ,polyps are clones ,all of which carry an APC Mutation .The loss of corresponding allele on the homologous copy of Chromosome 5 is not necessary for polyp formation .The first step and the relative order of subsequent mutations .Subsequent Mutations in polyp cells causes Intermediate stages of tumor formation .Mutations in the ras onco gene on chromosome 12 ,cause polyp to grow larger and to devlop finger like outgrowths .This is the Intermediate adenoma stage .

  To progress further ,a polyp cell must acquire Mutations in the DCC (Detected Colon Cancer) gene on chromosome 18 .
Mutations in both DCC alleles results in late - stage adeno-mas .Finally ,Mutation of the p53 gene causes the transition to a cancerous call .As described earlier , Mutations in p53 are pivotal to cancers including LUNG ,BRAIN as well as Colon Cancer .
Metastasis occurs after the formation of Colon Cancer ,and it's involves an unknown number of Mutational steps .