Science Questions

Why do cancer and AIDS patients lose weight so rapidly?

Sun, 4th Oct 2009

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Allison Dennis asked:

Why do cancer and AIDS patients lose weight so rapidly?


Chris -   Actually, this is a phenomenon thatís very well described.  People who get malignancies very often lose dramatic amounts of weight and people who get HIV also lose enormous amounts of weight.  What they both have in common is that the immune system is often driven into overdrive.  Itís pushed very hard.  But scientists didnít really know, aside from saying, it must be some kind of production of signalling hormones in the immune system.  They couldnít really tell exactly what the culprits were.  But then about a year Ė no, a couple of years ago now almost- a paper was published in Nature Medicine.  It was by Haiko Yonan et al and what they did was to find one of the factors that seems to cause this dramatic weight loss.  

They were using mice and they had mice in which they implanted a prostate cancer sample.  And those mice went on to lose dramatic amounts of weight and when the scientists compared the levels of various chemicals in the blood of the mice with healthy mice, they found that one chemical in particular, MIC-1, Macrophage Inhibitory Cytokine -1 was at very high levels.  And when they gave antibodies to that particular chemical, the mice didnít lose any weight.

So it looks like itís the immune system, trying to respond to the cancer or being manipulated or thwarted by the cancer and it makes these abnormal signals that it shouldnít make.  And they then cause the appetite centre in your brainís hypothalamus to go off kilter and it causes people to lose their appetite and stop taking in the right amounts of food.  So, they're burning off lots of energy, but they're not replacing the calories.  And as a result, they end up getting too thin and they lose all that dramatic amount of weight.

The fact they've identified one of these factors is really good news because it kind of suggests that we might be able to reverse the process.


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Alison Dennis asked the Naked Scientists:

Why do end stage cancer and AIDS sufferers lose weight so rapidly. Is there an increase in metabolism? Those on starvation diets seem to take much longer to become emaciated.

What do you think? Sparrowhawk, Fri, 3rd Oct 2008

The phenomenon of extreme and inappropriate weight loss seen amongst terminal patients with malignancies is referred to as cancer cachexia; people can look gaunt, wasted and very weak.

For a long time scientists suspected that the cause was inflammatory chemicals called cytokines that are normally produced by immune and other cells to regulate the activity of other branches of the immune system. Researchers think that cancers inappropriately pump out these signals into the bloodstream where they cause knock-on effects including suppressing appetite. The identity of the signals responsible wasn't known, however.

But recently scientists announced that they have successfully tracked down one of the chemical culprits, a molecule called MIC-1 or macrophage inhibitory cytokine 1. Blood levels of MIC-1 in patients with prostate cancer were directly correlated with tumour-associated weight loss. And when prostate cancers were transplanted into mice the animals lost weight except when an antibody designed to soak up MIC-1 was give at the same time.

MIC-1 seems to bind to receptors (chemical docking stations) in the brain's hypothalamus causing appetite suppression. The ability to block the effect in animals strongly suggests that the same trick could work in human cancer victims, helping them to remain better nourished and therefore stronger.

Reference - the work above was published in Nature Medicine in November 2007 and was carried out by Heiko Johnen et al.

Nature Medicine 13, 1333-1340 (1 November 2007) | doi:10.1038/nm1677

Chris chris, Fri, 3rd Oct 2008

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