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What are the two categories of causes of cancer?
exogenous and endogenous causes
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What are exogenous causes?
- from outside the body
- chemical
- physical
- viral
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What are endogenous causes of cancer?
- from within the body
- genetic factors
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Can exogenous factors change normal cell DNA?
yes
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What is a carcinogen?
substance that causes cancer
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What are the three steps to identify a carcinogen?
- clinical studies
- epidemiologic studies
- experimental studies
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What are clinical studies?
- information gathered by practitioners treating cancer patients
- case studies, retrospective studies, prospective studies
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What are case studies?
individual cases published in journals, or presented at meetings
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What are retrospective studies?
- information gathered from similar cases and analyzed
- need detailed medical records
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What are prospective studies?
- carefully planned clinical trials
- similar type patients
- controlled factors
- control groups
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What is epidemiology? What does it include?
- the study of disease in population
- includes genetic, cultural, and environmental causes of disease
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What are experimental studies?
performed on tissue cultures of on lab animals which are exposed to possible carcinogens
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What experimental study was done in japan in 1915?
- japanese scientists painted tar on ears of rabbits - which induced tumors
- these tumors were found to be caused by dibenzanthracene - a chemical found in tar, soot, and tobacco smoke
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What types of chemical carcinogens cause cancer?
- natural
- man-made (drugs, industrial)
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How can drugs cause cancer?
- many chemotherapy drugs are carcinogenic like cyclophosphamide
- secondary cancer may develop years or decades later but this isn't a concern in animals due to shorter life spans
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How do industrial conditions cause cancer?
workplace exposure like asbestos
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What is dibenzanthracene and what kind of cancer does it cause?
- tobacco smoke, tar
- lung cancer
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What is aflatoxin and what kind of cancer does it cause?
- fungus (Aspergillus flavus)
- liver cancer
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What is estradiol and what kind of cancer does it cause?
- hormone
- breast and uterine cancer
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What is naphthylamine and what kind of cancer does it cause?
- from aniline dyes (dye and rubber industry)
- bladder cancer
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What are some physical carcinogens?
- some trauma
- mostly radiation like ultraviolet light, x-rays, radioactive materials, atomic bombs
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What kind of carcinogen is ultraviolet light?
skin carcinogen
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How does ultraviolet light cause cancer?
exposure to the sun - outdoor pets, livestock, lack of shade, sunbathers, outdoor workers
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What types of cancer does ultraviolet light cause?
- basal cell carcinoma
- melanoma
- squamous cell carcinoma (ears of white cats, cancer eye of white faced cattle)
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When did we start using x-rays?
1895
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What is fluoroscopy and can it cause cancer?
- "x-ray movies"
- yes, even riskier than regular x-rays
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What kind of cancer did workers in uranium mines die from in the early 1900's?
lung cancer
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What kind of cancer did factory workers painting phosphorescent radium watch dials die from in the 1920's?
bone cancer
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Madam Marie Curie and her daughter, Irene Joliet-Curie were radium researchers, what kind of cancer did they die from?
leukemia
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What kind of cancer is increased when exposed to an atomic bomb?
leukemia and thyroid cancer
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What are some natural biologic carcinogens?
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Which parasites can cause cancer?
- Schistosoma haematobium
- Spirocerca lupi
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What is Schistosoma haematobium and what kind of cancer does it cause?
- human bladder fluke in Egypt
- bladder cancer
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What species does Spirocerca lupi affect and how does it cause cancer?
- domestic dogs, wild dogs and cats
- nematode located in wall of esophagus, aorta, or stomach
- parasite forms nodule - may convert to fibrosarcoma or osteosarcoma
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It has long been known that certain tumors can be transmitted by _____.
cell-free extracts
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What are some examples of tumor viruses?
- papillomavirus - common warts in people
- poxvirus - fibromas in rabbits
- herpesvirus - marek's disease in chickens
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What kinds of cancers can be hereditary?
- breast, colon cancer in people
- harder to document in animals
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Tendency to develop cancer is a _____ trait.
polygenic
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