The increased rate of cancer among heart patients has been found in other studies, but the large sample in this analysis allowed the researchers to note differences between types of cancer. Patients with heart failure had more than double the risk for cancers of the lip, oral cavity and pharynx. The risk was 91 percent higher for lung cancer and other respiratory cancers, 86 percent higher for female genital cancers, and 83 percent higher for skin cancers. People with heart failure had a 75 percent higher risk for colon cancer, stomach cancer and other cancers of the digestive system. Women with heart failure had a 67 percent higher risk for breast cancer, and men a 52 percent higher risk for cancer of the genital organs.
“I think it is an interesting retrospective cohort study,” said Dr. Girish L. Kalra, a senior cardiology fellow at the David Geffen School of Medicine at U.C.L.A., who was not involved in the work. “The primary shortcoming of the study is that the database did not allow investigators to control for the single greatest risk for developing cancer and heart disease: smoking. Cigarette smoking may be the common thread in this study.”
Still, while the strong connection with oropharyngeal and respiratory cancers suggests that smoking may be one explanation, the association remained robust for a broad range of cancers. The study also controlled for other factors linked to various cancers, including obesity, diabetes and advancing age, as well as frequency of medical consultations, which might lead to increased detection of cancers.
In addition to smoking, there are other possible mechanisms that could explain the link. For example, a previous study found that a well-known protein biomarker of heart disease that appears even before symptoms occur is also correlated with an increase in the risk for cancer. It is also possible, the researchers write, that chronic inflammation may be involved in both heart failure and cancer. Alcohol use has also been tied to a variety of cancers.
“There are more correlations between heart failure and cancer than just common risk factors,” said the senior author, Mark Luedde, a cardiologist at the University of Kiel in Germany. “Heart failure is not a disease of the heart. It is almost always a disease of the heart and other organs. The importance of comorbidities for the prognosis and quality of life of those affected cannot be overestimated.”