Does Organ Function Determine Cancer Susceptibility? — Science Daily Dose

Research article // Evolutionary Ecology of Organs: A Missing Link in Cancer Development?

Some background // In the past few weeks I’ve focused a bit on why treating cancer is difficult (check out part 1 and part 2 to read more). As scientists, part of the reason that we are in a constant search for new and improved therapies is that we don’t fully understand how cancer works. We don’t understand fully how cancers can spread and metastasize, or exactly what determine when a tumor is more likely to metastasize to one organ than another. When scientists study cancer, there are many places to look for new ideas. We can look at what makes some tumors more aggressive so that we can imagine targets for new cancer therapies. We can instead also look at what makes other tumors less aggressive or prevents them from growing, so that hopefully this can provide insight into strategies that might be protective against cancers.

The question to consider // Does evolution play a role in determining which organs are the more common sites of cancer and metastasis?

There are certain organs that are more susceptible to tumors, and organs where tumors are incredibly rare. Researchers in this study wanted to ask questions about why that is the case, in the hopes that it can provide insight into future cancer treatments.

There are two main ideas about what makes cancers in certain organs (like the heart) to be incredibly rare, while others are much more common: intrinsic and extrinsic causes. In other words, is there a particular property that is inherent to the organ (intrinsic) that makes it more “resistant” to forming a tumor? Or are external factors (such as smoking) more important to determine which organs develop cancers?

Instead, researchers in this paper propose a third option. Cancers are rare in organs that are vital for “survival and Darwinian fitness.” In other words, organs that are not paired (you have two lungs, two kidneys), or that are small (a tumor on a small organ would overwhelm it, while a tumor on a small organ might still allow the organ to function), or tumors that are needed for survival and reproduction have adapted to be more resistant to tumor formation. Of course, another theory could be that organs that are larger or come in pairs evolved to be that way precisely because they are more susceptible to tumors.

By thinking about cancer in this new way, it might be possible to learn more about it. There are some clues that provide insight into this theory. In autopsies of patients who died of causes other than cancer, microscopic tumors can often be found in organs. Why did the tumors grow at all, but not become larger and spread? This is where the idea of evolution comes in. Perhaps the tumors appear because the natural selection is weak. In other words, if a few tumor cells are likely not to have a big impact in the organ where they are growing, it would take more energy to eliminate or fight against them than it would take to allow them to stay there. So maybe the cost of eliminating the tumor cells is simply not worth the benefit of keeping them there.

That could be an interesting insight for biologists. If we can figure out why these cells appear, or what keeps them from growing bigger, it might help us to develop therapies to prevent them from growing in the first place, and from spreading to other parts of the body, and to treat existing tumors.

One final question // There’s a lot more research that needs to be done, but this is an interesting new way to think about strategies for cancer treatment and prevention. Of course this leaves the question (a good question, proposed by the authors): is it possible this same way of thinking could be used to learn more about other diseases, and not just cancer?

// tl;dr

Tumors are more common on organs like the lungs (which come in pairs) and the liver (which is quite large) than in the heart, testis and ovaries (organs that are vital for survival and reproduction). The researchers propose that this is likely due to the evolution of our organ systems. Either organs that are more susceptible to developing tumors grew to be large or in pairs, or that vital organs for survival and reproduction developed ways to prevent tumors from growing there.