In some ways, the heart is quite a vulnerable organ. Cardiac complications such as heart attack, cardiac arrest, or heart failure are common. But interestingly, of the many diseases that may affect the heart, cancer is not one of them. For example, we often hear about cancer in the prostate, breast, colon, skin, etc., but rarely of the heart. How is this vital organ different?
How Cancer Happens
To understand why we don’t get heart cancer, we must first understand how cancer comes to be. As you may already know, our cells are constantly regenerating in order to repair the body’s damages. On a daily basis, we expose ourselves to tons of harmful agents such as toxins, acids, certain enzymes, and UV rays. As our cells and tissues become damaged, stem or progenitor cells actively divide to replace what’s lost.
Each time a cell divides, it copies its DNA – and sometimes, mistakes happen. To be clear, cells have incredibly robust error-checking mechanisms and DNA repair processes to eliminate said mistakes. However, the human body also has ~37 trillion cells, some of which are actively dividing (such as in the skin which constantly experiences cellular stress). Thus, it’s not surprising that genetic mutations arise. If cells accumulate enough genetic mutations (about half a dozen is enough), it may become cancerous. In other words, the body’s healing process also makes it more likely for cancer to develop. (Ironic, isn’t it?)
Why Doesn’t the Heart Get Cancer?
So we know that as more cells divide and regenerate, the chances for cancer to grow also increases. How does this apply to the heart? Unlike the rest of the body, the heart actually has very little cell regeneration. In fact, the amount of cell division that takes place is so low that only 50% of the cells in our hearts are ever replaced. That means that half of the heart cells we’re born with stay with us for our entire lives. So why don’t we get heart cancer? There’s no chance to. Without active cell division, there is very little opportunity for replication mistakes to occur and thus, true heart cancer, originating from heart cells, is extremely rare. The cases of heart cancer you might have heard about are actually cancers of the supporting cells in the heart or cancers that have spread from other parts of the body.
Now the interesting question is why. Why doesn’t the heart regenerate itself? Is it unable to?
Why The Heart Doesn’t Regenerate
One reason why the heart doesn’t regenerate (or get cancer) is that it simply doesn’t need to. As mentioned previously, most of the body is constantly exposed to stressors which cause cellular damage and thus drive regeneration. Now if you think about the heart’s environment, it’s not exposed to much more than blood. As a result, instead of having to divide and repair itself, the heart is able to focus on other things (like pumping.)
Other Matters of the Heart
Another unique characteristic of the heart is the number of chromosomes in its cells. Scientists who study hearts across the animal kingdom have found that this number actually varies amongst species. Mice and human hearts, which are unable to repair themselves, actually have a high proportion of polyploid cells (even though the rest of the body is comprised of diploid cells). In contrast, the hearts of zebrafish have more diploid cells and can also efficiently regenerate after injury.