Question of the Week Podcast

Question of the Week episode

Mon, 10th Dec 2012

Do foetuses get cancer?

"Stripped" human oocyte; granulosa cells that had surrounded this oocyte have been removed. (c) RWJMS IVF Laboratory

We find out if foetuses get cancer, 15 yr old Louis from London got in touch asking: their cells divide rapidly, so surely they can make genetic errors and get cancer? Plus we ask, how do touch sensitive gadgets work?

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  • Do foetuses get cancer?

    Do foetuses get cancer? Their cells divide rapidly, so surely they can make genetic errors and get cancer. Thank you in advance. Louis CH

 

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There have been cases where a mother's cancer has crossed the placenta and taken root in the foetus. The foetus' immune system cannot recognise and fight off these "foreign" invaders. http://en.wikipedia.org/wiki/Cancer#Other

Human cells can divide up to about 40-60 times, the Hayflick limit http://en.wikipedia.org/wiki/Hayflick_limit

The average human cell has a mass of 1 nanogram (10-12 kilograms  http://en.wikipedia.org/wiki/Orders_of_magnitude_%28mass%29)...

A 4kg newborn baby has about 4x1012 cells.

Very roughly, this implies around 42 cell divisions from a fertilised egg up to birth

and another 4 divisions from birth to a 64kg adult (ignoring a whole bunch of factors, including wear and tear!)

So an adult cell starting to multiply rapidly would run into the Hayflick limit after around 14 cell divisions, producing about 15000 cells, much less than a milligram (which seems hardly life-threatening)

This seems to give some reasonable cancer protection for an adult, but provides little protection from a cancer starting in a young foetus



It takes somewhere around half-a-dozen important mutations for a cell to evade the Hayflick limit and become a cancer growing out of control. For example:

Disabling error-checking in DNA duplication

Turning off normal tissue growth regulation

Turning on an extra blood supply

Turning on telomerase

Turning off apoptosis
Disabling tumour-suppressor genes
Forming metastasies




The human DNA is around 3.2x109 base pairs, suggesting 1 mutation for every 3 cell divisions.
By the time a cell line reaches 42 divisions, we could expect a random collection of about 14 mutations in each cell, just from copying errors alone.
In the unlikely event that DNA repair mechanisms were completely disabled, the rate of copying errors would increase dramatically:

From the normal level of 2 mutations in 6 divisions

To an astounding 700 million mutations in 6 divisions. This would almost certainly interfere with tumour-suppressing genes (if it didn't kill the cell first).


It is certainly possible for a foetus to develop a cancer, if enough of these mutations disable the critical genes. A cluster of mutations like this could occur in a single cell due to normal rates mutation during cell division up to birth, but it is fairly unlikely.

If a baby inherits some of the well-known cancer genes like BRCA1 or BRCA2 (which are part of the DNA repair mechanism), that already places them 1 or 2 steps down the path to developing a cancer

Stem cells often express telomerase, which removes one more barrier to developing cancer. They divide more, and can build up more copying errors.


Conclusion
There are many causes of infant mortality, but cancer originating in the foetus is well down the list.

However, such a combination of mutations is even more likely to occur and cause a fatal cancer in someone aged 70 or 80, who has a declining immune system, and has been exposed to a lifetime of cell division errors, UV (& other) radiation, viral infections, cigarette smoke and other environmental carcinogens. evan_au, Tue, 4th Dec 2012




https://en.wikipedia.org/wiki/Sacrococcygeal_teratoma

Mutations very early on could cause spontaneous abortion, so the "live birth" statistics are going to be an underestimate. RD, Tue, 4th Dec 2012

Is there anyway that a simple zygote can end up as a cancerous cell in itself? What would that result in? Supercryptid, Wed, 5th Dec 2012

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