I actually had another email about this. It stems from 1907 and it comes from an American doctor, Duncan MacDougall, who tried to work out how much your soul weighs. People have thought for thousands of years that there's some life force or soul that makes us human, and when we die it leaves the body. As it exists, it must be made of something, and if it's made of something then it must weigh something. The easy way to find out how much it weighs is to weigh someone at the moment they die. What he did was to recruit six terminally ill patients, and selected ones that wouldn't thrash around too much at the time of death because that would obviously skew his results a little bit. He had this special bed balance made up and installed into his hospital. One patient lost, he says, three fourths of an ounce, which is twenty one grams. He then published this in American Medicine and it got picked up as 'the soul weighs 21 grams' and there was a massive splash about it. But actually it's wrong, because if you go and examine the rest of his results more carefully, you'll find that there's a little bit of a bias in how he's reported it. One of the people lost 21 grams; two of the people were discounted from the study for 'technical reasons'; a third person lost a load of weight and then put it back on again; and the final two lost a load of weight and then lost a load more, suggesting that they died more than once - I'm not sure! This is where this stems from, and it just shows that if you do careless research it can be quickly picked up and turned into a massive urban myth.

There's no doubt about it, the best way to stop cancer would be to stop breathing or live in an oxygen-free environment. But it's not a good recipe for a lifestyle. Human beings, all organisms, are a compromise. We live in this very dangerous gas that does us a lot of damage, but it also happens to be the way that we generate energy, and mitochondria do indeed generate a lot of these oxygen radicals and they cause a lot of problems for us as we get older.

Radiation is everywhere so there's nothing you can do about it. But radiation is bad for cells because you get these high energy particles shooting through your body and through the cells. They damage the DNA directly and they generate these reactive species which further damage the DNA and cause mutations. Most mutations don't cause any problems, but very rarely you'll mutate a gene that's fundamental in regulating cell growth, survival, or where the cell moves and spreads, and then you're on the way to potentially forming a cancer. So in the right places, radiation is good because it can be used in the right places and the right doses to destroy cells. Radiotherapy is used for a variety of cancers, including some brain cancers. Part of the problem seems to be that a lot of the cancer cells, by the time they're presented as a clinical disease, pretty much don't care how much damage they have anymore. In order to become the tumour cell they have, they've had to throw off all the responsive mechanisms that would normally curtail the cell from growing, and you end up with replicating glass beads that you can't do very much about.

The reason that chemotherapy makes your hair fall out is that the current chemotherapy treatments we have are very aggressive drugs. They kill cells that are growing fast. This usually means cancer cells, which grow quickly, but also your skin cells, your hair cells and your gut cells are all growing quickly. They are also affected by the drugs, and that's why you get side effects such as feeling sick and your hair falling out. Hopefully some of the new treatments that Fran and people are working on are going to be much more targeted and only hit cancer cells and not the other cells.

It's very difficult to talk about individual cases, and in general it's very hard to say. I just hope that he has very good treatment. It's extremely rare in someone so young. Most cancers in that age group are skin cancer, melanoma and testicular cancer, so I think that it would be very difficult to pin it down on any particular thing.

That's actually an important question and one of the questions I ask my students when I'm teaching: why does cancer kill? It's not simple. I think what it tells us is that if cells don't grow in the right way and they start mucking up the blood supply and the nerves and the normal function of tissues, your body can't cope and that's what kills you. So cancers basically erode the normal functions of your organs and your tissues, and that's why it kills you, although different cancers kill in different ways. In fact you can keep cancer cells growing forever, you can take them out of a patient and put them in a petri dish and off they go forever and ever. There are some cancer cells that have been around for so long that they mass of cancer cells in the world is something like a thousand times that of the original patient. So in principle you could live forever as a large lump, but I wouldn't want it.

The idea is that your immune system, which normally fights infection and bacteria, can also respond to any tumour cells that arise in your body. It's something that people have been thinking about for about 50 years. I started my career off as a tumour immunologist, as it's called. I think the jury's still out. There's no doubt that you can raise antibodies and cells that kill enemies; you can raise those against cancer cells. Whether you can do that naturally or whether we can make it happen by manipulating things is still not clear, but it's a very promising area. So in principle the idea is sound; we just don't know how effective it's going to be.

Stem cells are being used in many ways. One idea, and it's still an idea, is that cancers actually arise from stem cells. These are the small number of cells in the body that are capable of reproducing indefinitely. Most cells in the body don't. They are usually either differentiated or can only go a few times and then they cop out. The idea is that cancer cells, because they can propagate indefinitely, arise from a stem cell compartment. This is still a new idea and there are a lot of good arguments going on about it, but we really don't know. The other idea is that if you expose a patient to a severe therapy and you start to kill off normal tissues, if you could keep the patient alive and repopulate those normal tissues, then the patient will make a full recovery. To do that you would need to propagate the stem cells in the patient in those tissues.

We don't really know in detail, but what we know sort of happens is that as soon as the messenger RNAs are made, they are complexed in this protein particle. That particle is then transported in a system that requires a lot of energy through special pores in the nucleus and out the other side. It then attracts via a chemical reaction and congregates with various machinery for activating synthesis of those proteins. If you're asking me how each individual particle is moved around, that's the big mystery. How do cells know who they are and what they are and how do the bits themselves know who they are and what they are? I wish I knew!