cancer arises from changes in a single cell. these changes are the result of the interaction between a person’s genetic factors and three categories of external agents, including:
- physical carcinogens, such as ultraviolet and ionizing radiation;
- chemical carcinogens, such as asbestos, components of tobacco smoke, aflatoxin (a food contaminant) and arsenic (a drinking water contaminant); and
- biological carcinogens, such as infections from certain viruses, bacteria or parasites.
about 30% of cancer deaths are due to the five leading behavioral and dietary risks:
- high BMI (body mass index)
- not enough fruit and vegetables
- not enough sports
cancer generally arises from a disbalance between proliferation and cell death.
around 5000 of the human’s 25000 genes are responsible for ensuring that the copies of the DNA from one generation to the next are equal. These tumor suppressor genes decide about the activation of repair processes, stop the cell cycle until repair procedures are completes or activate the programmed cell death if the repair was not successful. Further, there are proto-onco-genes for the start or continuation of the proliferation of the cell and its differentiation.
5–10% of cancers are due to genetic defects inherited from a person’s parents.
If a person is found to have a mutation of either BRCA1 or BRCA2, their close relatives (parents, siblings, and children) have a 50% chance of having a mutation, too.
BRCA1 mutations: breast and ovarian cancer
BRCA2 mutations: male breast cancer, pancreatic cancer, and prostate cancer.
further cancer related genes: HNPCC, MLH1, MSH2, MSH6, PMS1, PMS2
cancer can also be driven by epigenetic changes:
- DNA methylation (why not acetylation?)
- histone modification (histones package and order the DNA into units called nucleosomes)
- changes in chromosomal architecture
each of these epigenetic alterations serves to regulate gene expression without altering the underlying DNA sequence.
- evasion of apoptosis (programmed cell death)
- self-sufficiency in growth signals
- insensitivity to anti-growth signals
- sustained angiogenesis (growth of new blood vessels)
- limitless replicative potential
- reprogramming of energy metabolism
- evasion of immune destruction.