13. How And Why Neoplasms Occur Flashcards
What factors account for cancer risk?
Intrinsic - eg heredity, age and gender (especially hormonal.
Extrinsic - eg environment and behaviour.
What are the 5 leading behavioural and dietary risks that account for 30% of cancer deaths?
High BMI. Low fruit and vegetable intake. Lack of physical activity. Tobacco use. Alcohol use.
What accounts for 85% of a populations cancer risk?
Extrinsic factors (chemicals, radiation, infection).
How much time is there between carcinogen exposure and malignant neoplasm onset?
Long delay
What is the relationship between risk of cancer and carcinogen dosage?
Risk of cancer depends on total carcinogen dosage
True or false, there is no organ specificity for particular carcinogens?
False, there is sometimes organ specificity for particular organs
Why do industrial carcinogens have an effect primarily on the relevant workers and the effect of tobacco smoke is largely limited to smokers?
The risk of cancer’s dependence on dosage.
Give 3 classifications of mutagenic chemical carcinogens
Polycyclic aromatic hydrocarbons. Aromatic amines. N-nitroso compounds. Alkylating agents. Diverse natural products eg aflatoxin, asbestos.
What are pro-carcinogens?
Chemicals that are only converted to carcinogens by the cytochrome P450 enzymes in the liver.
What are complete carcinogens?
Carcinogens that act as both initiators and promotors.
What is radiation?
Any type of energy travelling though space
What does ultraviolet light penetrate?
No deeper than skin
What does ionising radiation do in the body to atoms? Give 2 examples
Strips electrons from atoms.
X-rays and nuclear radiator arising from radioactive elements (alpha particles, beta particles, gamma rays).
How does radiation damage DNA?
Directly and indirectly by generating free radicals.
What in the DNA is damaged by ionising radiation?
DNA bases, and causes single and double strand DNA breaks
In what 2 ways can carcinogenic infections act on cells?
Directly affect cell growth by affecting genes that control cell growth.
Indirectly affect cell growth by causing chronic tissue injury where the resulting regeneration acts either as a promotor for any pre-existing mutations, or else causes new mutations from DNA replication errors.
How does HPV act as a direct carcinogen to cause cervical carcinoma?
Expresses the E6 and E7 proteins that inhibit p53 and pRB protein function respectively, both of which are important in cell proliferation (control the cell cycle).
Give an example of a virus that are indirect carcinogens causing chronic liver cell injury and regeneration
Hepatitis B and C
How does Helicobacter pylori increase the risk for gastric carcinomas?
Causes chronic gastric inflammation
How does HIV lead to an increased neoplasm risk?
Acts indirectly by lowering immunity, allowing other potentially carcinogenic infections to occur
What is the two hit hypothesis?
Need both alleles of a gene to mutate to cause a neoplasm. Therefore in familial cancers, first hit is delivered through the germline and effects all the cells in the body. The second hit is a somatic mutation. As only one mutation is needed, neoplasm can develop quicker.
What are tumour suppressor genes?
Inhibit neoplastic growth.
What are proto-oncogenes?
When activated, enhance neoplastic growth
Do tumour suppressor genes and proto-oncogenes need 1 or 2 hits to allow a neoplasm to grow and why?
Tumour suppressor genes - both alleles much be inactivated, as inhibit neoplastic growth, so even with just one normal allele they can still do that.
Proto-oncogenes - one allele, as once activated it enhances neoplastic growth.
