People Are Asking Why They Have Never Heard Of Heart Cancer

"Since cancer happens where there are cells in your body," Reddit user Exciting-Match-2151 said, "why have I never seen such thing as heart/muscles cancer?"

So, why is that? Well, the reason you hear about the other types of cancer so much is because of how prevalent they are in humans.

"Cancer is a leading cause of death worldwide, accounting for nearly 10 million deaths in 2020, or nearly one in six deaths," the World Health Organization explains, adding that "the most common cancers are breast, lung, colon and rectum and prostate cancers".

These cancers, as well as more aggressive cancers like pancreatic cancer, are regularly the subject of awareness campaigns. Even if you don't know someone personally affected by them, there's a good chance you'll hear about them every now and then. 

The primary reason you don't hear about heart cancer so much isn't because it doesn't exist, but because of how rare it is. One estimate suggests primary heart tumors affect between 0.0017 percent and 0.028 percent of the population, and only 25 percent of those cases are malignant, or cancerous.

“Throughout my career, I've probably seen malignant primary cancers of the heart maybe two or three times,” Dr Tochukwu Okwuosa, a cardiologist and director of cardio-oncology at Rush University Medical Center in Chicago, told IFLScience.

“They're not very common malignancies, and that's the reason why most people don't talk about them often,” she added.

As well as this, heart tumors are also most often metastases, or cancer that has spread from another nearby organ. Awareness campaigns may be better focused on the primary cancer, as by the time it has spread to the heart, the prognosis for the patient is not great.

"When they're malignant, they're really malignant, unfortunately," Okwuosa added. "Nobody ever wants to be told that the tumor in their heart is a malignant cancer because the chances of curing it is very low and the chances of death is very high, even with chemotherapy."

So why is cancer in the heart so rare? It's because heart cells are "terminally differentiated", or reach a point where they stop dividing.

"Even though the heart is the first organ to form and start working during early development, cells in the adult heart divide very few times after birth, with division dramatically declining after age 20," Julie Phillippi, Associate Professor of Cardiothoracic Surgery and Bioengineering at the University of Pittsburgh, explained in a piece for The Conversation.

"In fact, less than 50% of heart cells are replaced over the course of an average human life. That means half of the heart cells you’re born with will be helping pump blood for your entire life. This low rate of cell division in the adult heart likely serves as its primary defense against cancer. The less often a cell divides, the fewer opportunities there are for mistakes during DNA replication."

In short, the main reason you don't hear about heart cancer that often is that it is an especially rare, if deadly, disease.