[DiscoverDave]

As a spin-off of the Question-of-the-Week about immortal life forms, we know that cancer cells divide more-or-less continuously, but do "old" cancer cells ever die from "old age", or do they continue to live indefinitely (repairing themselves etc)?

[EatsRainbows]

Im not certain, but i have an inkling i read somewhere that some mutations which cause cancer are not actually causing excessive cell division but a mutation upon the gene which controls programmed cell death... so they don't die when they should and you thus end up with accumulation.... again just an inklling!

[EatsRainbows]

During the process of DNA replication, small segments of DNA at each end of the DNA strand(telomeres) are unable to be copied and are lost after each time DNA is duplicated [10].The telomeres are a region of DNA which code for no proteins; they are simply a repeated code on the end region of DNA that is lost. Eventually, after many divisions, the telomeres become depleted and the cell commences apoptosis.This is a defense mechanism of a cell to prevent replicating error that would cause mutations in DNA

http://en.wikipedia.org/wiki/Hayflick_limit

The enzyme telomerase allows for replacement of short bits of DNA known as telomeres, which are otherwise lost when a cell divides via mitosis.
In normal circumstances, without the presence of telomerase, if a cell divides recursively, at some point all the progeny will reach their Hayflick limit.[14] With the presence of telomerase, each dividing cell can replace the lost bit of DNA, and any single cell can then divide unbounded. While this unbounded growth property has excited many researchers, caution is warranted in exploiting this property, as exactly this same unbounded growth is a crucial step in enabling cancerous growth.

http://en.wikipedia.org/wiki/Telomerase

Sounds as if in presence of telomerase, as apparently is present in cancer, the cell will not reach the point at which it undergoes cell death (apoptosis), even if it is mutated. Sounds to me as if it may not 'repair' nor does it have its usual 'use by' date so may become rather expired and continue on dividing no matter what..... I suppose this may not be 'indefinite' though, perhaps telomerase may run out or some such....

[Variola]

As a spin-off of the Question-of-the-Week about immortal life forms, we know that cancer cells divide more-or-less continuously, but do "old" cancer cells ever die from "old age", or do they continue to live indefinitely (repairing themselves etc)?

It really does depend on the genetic mutations present in each cell, too much instability causes apoptosis as the cell is no longer sustainable. A new cell resulting from cancer cell mitosis could pick up another mutation that causes it's death
Cancer cells that are found in the centre of tumors are often dead, due to lack of nutrients/oxygen caused by the competition of their neighbouring cancer cells. All cells have their natural life span, and usually unrepaired major mutations in them cause apoptosis, but cancer cells have learnt to avoid this. However I am not sure cancer cells would live any longer 'naturally' (I.e not apoptosis) than any other normal cell.
I might investigate as I am curious now...

[Nizzle]

Some mutations cause an excess production of NF-κB, which is a transcription factor that stimulates cells to proliferate (divide) AND protects the cell from apoptotic signals.
Another known cancer mutation is an error in the I-κB (inhibitor of NF-κB) which would have the same effect as an overproduction of NF-κB.

Such cells, which are protected from apoptotic signals 'refuse' to go to programmed cell death stage, even if they should.