In my opinion cancer cells do not choose really. They are able to do both: metastasis and homing. Cancer cells are such a heterogenous population (as we human, but very most humans are no cancer cells ;) ) and they are under pressure: immunsystem, environmental conditions like need for growth signals, nutrition, oxygen, etc. (as you already said). Sure, some of them can survive partially under unconvortable conditions, but this leads to an activatation of cell programs to gain functions (e.g. ability to migrate, avoid apoptosis) to overcome problems (e.g. immunesystem, hypoxy). Additionally cancer cells behave sometimes like stem cells during organ/organism development (keyword: EMT, epithelial-mesenchymal transition). Indeed, cancer cells are not really stem cells, they gain some stem cell like functions without efficient control of these functiuons.

To make long story short: cancer cells develop during progression. Some cancer cells of the huge heterogenous population will gain functions due to various environmental conditions as well as cellular conditions (like mutations due to loss of efficient control systems). This leads to subpopulations able to invade and metastasis.

P.S.: This is a very complex matter, therefore there are much more to say, maybe the Review from Hanahan and Weinberg is interesting for you

http://www.ncbi.nlm.nih.gov/pubmed/21376230

You can answer this..!!

I am not sure, if there is a definite answer. One answer may be the survival of the cells when the conditions (e.g. nutritions, supply with oxygen) is getting worse. Cells can than migrate to another site and survive.

In my opinion cancer cells do not choose really. They are able to do both: metastasis and homing. Cancer cells are such a heterogenous population (as we human, but very most humans are no cancer cells ;) ) and they are under pressure: immunsystem, environmental conditions like need for growth signals, nutrition, oxygen, etc. (as you already said). Sure, some of them can survive partially under unconvortable conditions, but this leads to an activatation of cell programs to gain functions (e.g. ability to migrate, avoid apoptosis) to overcome problems (e.g. immunesystem, hypoxy). Additionally cancer cells behave sometimes like stem cells during organ/organism development (keyword: EMT, epithelial-mesenchymal transition). Indeed, cancer cells are not really stem cells, they gain some stem cell like functions without efficient control of these functiuons.

To make long story short: cancer cells develop during progression. Some cancer cells of the huge heterogenous population will gain functions due to various environmental conditions as well as cellular conditions (like mutations due to loss of efficient control systems). This leads to subpopulations able to invade and metastasis.

P.S.: This is a very complex matter, therefore there are much more to say, maybe the Review from Hanahan and Weinberg is interesting for you

http://www.ncbi.nlm.nih.gov/pubmed/21376230

Martin's answer really covers it.

Cancer cells do not really NEED to migrate. But as the cancer progresses, new mutations arise and cells acquire new properties. If the mutation cause loss of attachment and invasion into blood vessels cells will just "go with the flow".

HOWEVER, because they have learnt to grow in one environment, not all - in fact MOST - detached/invasive cells tend NOT to survive outside their tissue for the very same reason. This needs to appreciated. Thus, metastasis is a SLOW process and requires accumulation of mutations. The more mutations, the more chance of acquiring ability to grow in a different tissue type. This a natural phenomenon that has nothing to do with cell's choice. But once a cell acquires this phenotype there is no stopping it. It just is swept along and attaches to many other organs and can grow in them.

Because of the increased mutations required and the re-organization of the cell phenotype late metastases are difficult to kill, if you assume treatment for the primary tumor. Thus, also early cancer detection has better cure.

I will answer in a kind of "phyllosophical way"... They gain individuality. They don´t have any reason to stay at that site because they do not belong anymore to the whole organism. They become like "protozoans" and roam about, looking for other places to colonise. Bad for the cancer patient as a whole organism. And cancer cells are not aware they are killing the organism, they try to survive as individual cells.

Now, what prevents our cells to become independent? well, you know all the molecular stuff, inhibitory receptors, adhesion molecules, etc, etc, etc...

David: I see your point and treating them as cells each with their own programming is a nice thought.

I would emphasize, though, to embody cancer cells - or any other cells - with some decision making or "awareness" can cloud one's thinking. This is a purely stochastic - within the boundaries of biological process - and cells that 'survive' just do so by chance. Yes, there is some biological restrictions, but within that this a pure game of chance. If you see metastasis as "one of the many possibilities", one would realize why it happens at late stages.

??

Yes, I agree...don't misunderstand me !

I don't give cancerous cells an "awareness", but just the loss of all the regulatory mechanisms that arose during evolution to give rise to metazoans. Then, cancer cells would behave "on their own", and in fact, cancer is an excellent experimental evolutionary model in which some nearly "stochastic" (they target a surprisingly limited common pathways!) mutations give a growth/independence to cancer cells. We could complicate the system more, because at the end, solid tumours can also act as an independent "organ" directing their own blood supply, etc...but the question was about the reasons to metastasize. Obviously, not all tumours metastasize, and they can live in a "parasitic" type of way and that's fine. It is another solution to keep on living in organisms.

I think the original question is fantastically simple, and very complicated to answer ! So, I approached it in a simple way easy to be understood by anyone, not only scientists...

Hi everybody, I found very interesting this wide question and your answers.. I think that there is truth in each point of vues and here is mine. The main word is stochastic, already mentionned.. but if you look more widely at evolution, you will find the same pattern of competition, invasion and migration to colonize new areas in lots of organisms (humans included, of course).. The fact is when a species has to migrate, nothing tells that it will be the winner of the next competition race, unless it is alone that can survive the conditions there... I mean, sometimes, a clone or a subspecies is not perfectly adapted, with its new stochastic modifications, to survive where it is, but does better in another place. We know that cancer cells from one tumor are quite different. I think it is generally accepted that tumors are heterogenous populations of cells, each adapted to their microenvironmental conditions (more or less close of blood vessels, for example), and even if they arise from the same ancestor (or few ancestors), they are very different...not the overall behaviour, they are still cancer cells, dividing, escaping cell death, ect.. but their molecular, metabolic and signaling pathways are different. For having worked on Daphnia, a microcrustacean that can have a sexual or clonal reproduction mode, I have found lots of similitudes with cancer cells. Geographic parthenogenesis is a general term for species that have subpopulations (subspecies or species complexes, for people in evolution), generally polyploids (gene products modifications!), that are doing better living under extreme conditions (latitude, altitude, extreme cold or hot temperatures, deserts, ect..) than their temperate counterpats. They cohabit with their diploid counterparts only in the borders of their own territories and apparently are unable to survive in "normal" conditions. So, my point here, is that metastatic cells could be, such as those subpopulations, forced to live in conditions they can survive in. They are different cells, surviving in different conditions and attempts to kill their ancestors are unsuccessful on them because they are different. Maybe too much simple...

Why do you assume cancer cells do HAVE to migrate necessarily?

It that a rule I missed? Isn't that dependent on the specific cancer cells?

Definitely, cancer is heterogenous population, migration depends on microenvironment(growth factors, immune factors TNF IL6, IL 18 etc) and cellular genetic content at genetic point mutation or chromosal abnegation rate which varies from one cancer to other cancers, these all could be a deciding factor to potentiates its metastatic properties.

Certain Cancer cell within tumor mass, migrate from the site of origin, at early stage with less chromosomal abberation than the cells that have much higher number of abberation.

We know how cancer cell metastasis and when it metastasis,?

But we don't know why it has to metastasis ..By nature .does it favors tumor or host .?

Answer is unclear ..

Why Cancer cell has to metastasis by nature ? Does it favors tumor or host .? Answer is unclear ..