Thursday, May 2, 2013

Epidemiology of Cancer

Epidemiology of Cancer:
  • Over last 50 yrs, the overall cancer death rate has significantly incr for men; for women, it has fallen slightly
  • Increase in men is due to lung cancer
  • Improvement for women is due to decline in death rates from cancers of uterus, stomach, liver, and carcinoma of the cervix
  • Carcinoma of the lung has incr in both sexes; beginning to decline in men, but still incr in women
  • Carcinomas of breast are 2.5X more frequent than carcinomas of lung, but lung cancer is leading cause of cancer deaths in women
  • Decrease in death from stomach and liver carcinomas – perhaps due to decr in dietary carcinogens
Cancer incidence and cancer death for men:
Cancer incidence and cancer deaths for women:
Geographic and Environmental Factors:
  • Much of geographic differences are consequences of environmental influences
  • Rates of cancer for immigrants comes closer to US rates of cancer with each succeeding generation
Environmental Factors:
  1. UV rays
  2. Asbestos, vinyl chloride, 2-naphthylamine 
  • Persons more than 25% overweight have a higher death rate from cancer
  • Alcohol – incr risk for carcinomas of oropharynx, larynx, esophagus, and liver
  • Smoking – incr risk for cancer of mouth, pharynx, larynx, esophagus, pancreas, bladder, and lung dz
  • Smoking is single most important environmental factor contributing to premature death in the US
  • Alcohol and tobacco together – incr risk of cancers in upper aerodigestive tract
  • Risk of cervical cancer is linked to age at first intercourse and the number of sex partners
Age:
  • Each age group has its own predilection to certain forms of cancer
  • Striking incr in mortality from cancer in 55-74 y/o
  • Under 15 y/o:
  • Cancer accounts for about 10% of deaths in this group
  • Most common is acute leukemia and neoplasms of the CNS
Heredity:
  • For a large number of cancers, there are environmental influences and hereditary predisposition’s
Inherited Cancer Syndromes – inheritance of a single mutant gene greatly incr risk of developing a tumor
  • Tumors involve specific sites and tissues
  • Tumors w/in this group are often associated w/ a specific marker phenotype
  • Both incomplete penetrance and variable expressitivity are noted
Familial Cancers
  • Almost all sporadic cancers have been reported to occur in familial forms
  • Early age at onset, tumors arising in two or more close relative of index case, and sometimes multiple or bilateral tumors
  • Not associated w/ specific marker phenotypes

Autosomal Recessive Syndromes of Defective DNA Repair:
  • Example is xeroderma pigmentosa

Autosomal Dominant Neoplasia Syndromes
RB, retinoblastoma; FAP, familial adenomatous polyposis; APC, adenomatous polyposis coli; MEN, multiple endocrine neoplasia; RET, rearranged during  transfection; VHL, von Hippel-Lindau.

Defective DNA Repair Syndromes

  • ATM, ataxia-telangiectasia mutated.
  • *Ataxia-telangiectasia is also associated with cerebellar ataxia.




Acquired Preneoplastic Disorders:
  • A premalignant lesion is an identifiable local abnormality associated with an increased risk of a malignant tumour developing at that site. 
  • In the great majority of cases, no malignant neoplasms emerge
  • Certain forms of benign neoplasia also constitute precancerous conditions
  • Example – villous adenoma of the colon
  • Most benign neoplasms do not become cancerous
Precancerous (Premalignant) Lesions.

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