Food for thought: there are cancers of the brain, blood, lymph nodes, lungs, bone, and every other bodily organ, part, or system imaginable. Why, then, do we never hear about heart cancer — could it be our hearts, long symbolized as the root of loving emotion, are somehow immune to the dreaded disease? Unfortunately, the reason no one ever talks about heart cancer is much more mundane.

“We do have tumors that occur in the heart,” Dr. Jacqueline Barrientos, assistant professor, Hofstra North Shore-LIJ School of Medicine, told Medical Daily in an email, “but these are not as common, so you don't hear about them.”

Indeed, malignant heart tumors, known as rhabdomyosarcomas, are extremely rare. A sarcoma is a type of tumor that originates in the soft tissues of the body; a rhabdomyosarcoma occurs in the muscle tissue of the heart. Their incidence is estimated at less than 0.1 percent, based on a study of more than 12,000 autopsies, which identified only seven cases of any kind of primary cardiac tumor. (Primary tumors are those that have originated where they are found, and have not spread from some other part of the body.)

That said, “most cancers found in the heart have come from elsewhere in the body,” according to Dr. Timothy J. Moynihan of the Mayo Institute, meaning they are secondary tumors. To understand exactly what he means, it might be necessary to review the fundamentals.

Back to (Cancer) Basics

Our bodies have an astronomical number of cells — uncountable, really — though one estimate places the number at 37.2 trillion. When we are healthy, our many cells cooperate and share the vast work of our body, all while they go about their separate business of growing, dividing (to provide a replacement for themselves), and then efficiently dying. Cancer, then, is simply an aberration of these cellular processes.

Cancer begins when cells start to grow out of control. This is due to damaged DNA, the genetic material carried in the nucleus of each and every cell. Normally, a cell repairs any damaged DNA, or simply dies, but cancer cells do not repair or die. Instead, they divide and make many more abnormal cells with damaged DNA. Another unusual property possessed by cancer cells is they are able to grow into —invade, really — other tissues. Normal cells cannot do the same.

So, when Moynihan says cancers in the heart have come from “elsewhere in the body,” he is talking about just such an invasion — the cancer began somewhere else in the body, but now it has infiltrated the heart.

Dr. Mitchell Gaynor, clinical assistant professor at Weill Cornell Medical College, told Medical Daily the most common secondary tumors spreading to the heart “come from the lung, from the esophagus, and you can also see them from the liver, and the stomach. Even nests of leukemia cells form tumors in the heart.” More importantly, all of these different types of tumors “usually go to the right side of the heart,” Gaynor explained. “That’s where the blood enters the heart — on the right side.”

But a tumor is a tumor is a tumor, you say. How do doctors know where a tumor originates — especially when a new tumor may appear years later in a part of the body far from the original cancer site? When a new tumor appears, its cells are identical to those of the original tumor. So if a person had pancreatic cancer, say, and it spread to the brain, the tumor appearing in their brain, when viewed through a microscope, would look nothing like the tumor of a person with brain cancer — the cells of this brain tumor would look identical to pancreatic tumor cells.

If secondary tumors invade the heart, why is it so rare for primary tumors to develop there? According to Gaynor, the explanation begins and ends with our genes.

The Reason We Don’t Get Heart Cancer

As you likely know, we receive half our genes from our mothers, half from our fathers. While it would seem our genetic fate is sealed, “nothing could be further from the truth,” said Gaynor, whose new book on the subject, The Gene Therapy Plan, will be available in 2015. “We understand now how gene expression can be modified throughout your life… and that can create cancer,” he said.

In fact, our environment affects which genes become expressed (activated) as well as how frequently they become activated. And carcinogens coming from our food and environment are one of the many factors that influence which genes are activated or not.

“A lot of toxins are found in breast tissue, because there are a lot of fat cells there,” Gaynor explained. “And toxins are found wherever there is the most fat.”

While our bodies have some defenses against these contaminants, in the form of detoxifying enzymes, and while our bodies are supported by micronutrients which turn on tumor suppressor genes, dangerous toxins found in our fat tissue still modify our genes, which can result in cancers forming in the organs of our bodies, especially those containing fatty tissue.

This, then, is why the heart is so exceptional:

“There’s not a lot of fatty tissue [in the heart],” Gaynor said. Even more, “the heart’s enclosed in a membrane,” he explained. Known as the pericardium, this fluid-filled sac may itself become engulfed by cancer, with tumors metastasizing to the outside of it, but still it does its job of protecting our precious hearts.

So, even though cancer can happen anywhere there are cells, your heart remains virtually immune due to its muscular nature and the assistance of the pericardium. Smart heart.