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While speaking with my co-workers, the topic of tumors growing things came up. The examples were (and backed by images) of tumors growing a tooth, hair, and sometimes even more complex objects such as an eye.

My question is, could a tumor reproduce something that isn't typically found in the human body? Could it grow something that maybe a very distant ancestor would have had?

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I doubt it - tumours usually originate from differentiated cells where a few growth-restricting genes are turned off by mutations - I'd consider it extremely unlikely for them by chance to mutate and turn on the whole patterns of genes that work in alternation and conjunction to cause correct differentiation and produce tissues other than lumps. But I can't refer to any papers so I might be wrong and hence this is only a comment :) –  Armatus Jan 10 '13 at 19:21
    
@Armatus but we do see tumors in one place in a body grow something from a completely different place in the body. I know that isn't as drastic as something not currently found in the body, but it's still mutating far from what the cell was supposed to be. –  David Peterman Jan 10 '13 at 19:30
    
can you post links to your examples? just mentioning them is not as clear... –  shigeta Jan 10 '13 at 19:45
    
Isn't a tumour by nature something not inherently found in our body? –  GWW Jan 10 '13 at 19:53
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Would a mutated protein be a good example of something produced by a tumour that is not normally in our body? –  nico Jan 10 '13 at 22:27
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3 Answers

Teratomas are thought to be a particular type of cancer, present from early development. As cells which are essentially developmental cells, they seem to have a fairly unique ability to develop hair follicles, teeth and even structures like organs. Indeed malignant teratomas often require chemotherapy or radiation therapy.

I think this bizzarre quality of producing organs or hair etc, is the result of the fact that the origin cells are programmed to develop into these organs before they become tumorous. Later in life, we have no developmental stem cells in the body which will differentiate into organs and so other sorts of teratomas would seem to be unique.

Cancer cells are still cells programmed to perform the roles they started with, but they are usually not capable of generating whole functional tissue or organs. If they do they would normally be found amongst the tissue they would grow (e.g. liver cancer might produce tissue that looks like liver) so it would not have the unusual quality of teratomas of producing differentiated and specific tissues in isolation.

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Definitely NOT for cancer.

What you are speaking about are teratomas - results of incorrect development of stem cells. Stem cells are the type of cell that can become any other cell type. That way the growth of stem cell tissue may result in production of any organs.

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If you look at a cancer textbook (eg. Robert A. Weinberg's The Biology of Cancer), you'll find that by definition, a tumor arises from tissues normally found in the patient's body. There's a great deal more to it than just that simple statement, but given the context of the question, I think that answer should suffice.

In writing, "...tumors growing a tooth, hair...", I think you're talking about teratomas. These contain "normal derivatives of all three germ layers". These arise naturally from cells "...typically found in the human body..."

Cancer is a process where mutations in a single cell transform that cell into something that is by definition not "typically found in the human body." But a human cell transformed by mutation into a tumor (benign or malignant) is never (to the best of my knowledge) going to magically become a cell from another species or a very distant ancestor (ie. something that is not "typically found in the human body.").

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