Causes
Cancer is a diverse class of diseases which differ widely in their causes and biology. Any organism, even plants, can acquire cancer. Nearly all known cancers arise gradually, as errors build up in the cancer cell and its progeny (see mechanisms section for common types of errors).
Anything which replicates (our cells) will probabilistically suffer from errors (mutations). Unless error correction and prevention is properly carried out, the errors will survive, and might be passed along to daughter cells. Normally, the body safeguards against cancer via numerous methods, such as: apoptosis, helper molecules (some DNA polymerases), possibly senescence, etc. However these error-correction methods often fail in small ways, especially in environments that make errors more likely to arise and propagate. For example, such environments can include the presence of disruptive substances called carcinogens, or periodic injury (physical, heat, etc.), or environments that cells did not evolve to withstand, such as hypoxia[5] (see subsections). Cancer is thus a progressive disease, and these progressive errors slowly accumulate until a cell begins to act contrary to its function in the organism.
The errors which cause cancer are often self-amplifying, eventually compounding at an exponential rate. For example:
* A mutation in the error-correcting machinery of a cell might cause that cell and its children to accumulate errors more rapidly
* A mutation in signaling (endocrine) machinery of the cell can send error-causing signals to nearby cells
* A mutation might cause cells to become neoplastic, causing them to migrate and disrupt more healthy cells
* A mutation may cause the cell to become immortal (see telomeres), causing them to disrupt healthy cells forever