Although it’s not often mentioned, cancer can affect the heart. While most heart tumors, already a rare occurrence, are benign, malignant tumors can occur. The reason it isn’t often mentioned is that it isn’t often encountered. In one study, looking at more than 12,000 autopsies, only seven primary cardiac tumors were found. The Mayo Clinic, a leading medical center in Minnesota, sees about one case of heart cancer per year, and their website mentions heart cancer only in connection with its rarity. Sometimes cancer in other parts of the chest can spread to the heart, but that too is rare. It is fatal in very rare cases—it was cancer of the heart that killed one-time KISS drummer Eric Carr, as well as Catherine of Aragon some 450 years earlier.
When the heart does develop malignant tumors, whether primary or secondary, it can affect blood flow. In particular it stiffens the heart muscles, a condition called cardiac fibrosis, which means the heart has to work harder to pump blood. The tumors can also block the flow of blood through the heart or damage the heart valves. If the valves are seriously damaged by advanced-stage cardiac cancer, they may need to be replaced, but by this time, the cancer itself is likely terminal.
Because heart cancer is so rare, it is poorly studied compared to other forms of cancer. That means there’s no clear idea of risk factors specific to cardiac cancer, and know recommended course of treatment beyond those used for cancers by default. Unfortunately, treatments carry their own dangers. Radiation therapy used on or near the heart can also damage the heart muscle, and chemotherapy drugs can also be harmful. Radiotherapy also increases the risk of coronary artery disease.
Another consequence of the rarity of cardiac cancer is that it is difficult to detect. This is partly because it is so seldom diagnosed that few tests have been developed for it, and partly because it is so unusual that doctors do not typically expect to find it or think to look for it right away. However, researchers are developing universal blood tests that will enable screening for multiple forms of cancer, including the rare and unusual.