What are the two categories of causes of cancer?
exogenous and endogenous causes
What are exogenous causes?
- from outside the body
What are endogenous causes of cancer?
- from within the body
- genetic factors
Can exogenous factors change normal cell DNA?
What is a carcinogen?
substance that causes cancer
What are the three steps to identify a carcinogen?
- clinical studies
- epidemiologic studies
- experimental studies
What are clinical studies?
- information gathered by practitioners treating cancer patients
- case studies, retrospective studies, prospective studies
What are case studies?
individual cases published in journals, or presented at meetings
What are retrospective studies?
- information gathered from similar cases and analyzed
- need detailed medical records
What are prospective studies?
- carefully planned clinical trials
- similar type patients
- controlled factors
- control groups
What is epidemiology? What does it include?
- the study of disease in population
- includes genetic, cultural, and environmental causes of disease
What are experimental studies?
performed on tissue cultures of on lab animals which are exposed to possible carcinogens
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
What types of chemical carcinogens cause cancer?
- man-made (drugs, industrial)
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
How do industrial conditions cause cancer?
workplace exposure like asbestos
What is dibenzanthracene and what kind of cancer does it cause?
- tobacco smoke, tar
- lung cancer
What is aflatoxin and what kind of cancer does it cause?
- fungus (Aspergillus flavus)
- liver cancer
What is estradiol and what kind of cancer does it cause?
- breast and uterine cancer
What is naphthylamine and what kind of cancer does it cause?
- from aniline dyes (dye and rubber industry)
- bladder cancer
What are some physical carcinogens?
- some trauma
- mostly radiation like ultraviolet light, x-rays, radioactive materials, atomic bombs
What kind of carcinogen is ultraviolet light?
How does ultraviolet light cause cancer?
exposure to the sun - outdoor pets, livestock, lack of shade, sunbathers, outdoor workers
What types of cancer does ultraviolet light cause?
- basal cell carcinoma
- squamous cell carcinoma (ears of white cats, cancer eye of white faced cattle)
When did we start using x-rays?
What is fluoroscopy and can it cause cancer?
- "x-ray movies"
- yes, even riskier than regular x-rays
What kind of cancer did workers in uranium mines die from in the early 1900's?
What kind of cancer did factory workers painting phosphorescent radium watch dials die from in the 1920's?
Madam Marie Curie and her daughter, Irene Joliet-Curie were radium researchers, what kind of cancer did they die from?
What kind of cancer is increased when exposed to an atomic bomb?
leukemia and thyroid cancer
What are some natural biologic carcinogens?
Which parasites can cause cancer?
- Schistosoma haematobium
- Spirocerca lupi
What is Schistosoma haematobium and what kind of cancer does it cause?
- human bladder fluke in Egypt
- bladder cancer
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
It has long been known that certain tumors can be transmitted by _____.
What are some examples of tumor viruses?
- papillomavirus - common warts in people
- poxvirus - fibromas in rabbits
- herpesvirus - marek's disease in chickens
What kinds of cancers can be hereditary?
- breast, colon cancer in people
- harder to document in animals
Tendency to develop cancer is a _____ trait.