"Heart attacks increase the risk of developing cancer," is the completely inaccurate headline on the Mail Online website. The Mail was attempting to report on a study looking at cancer risk in people with heart failure. This is where damage to the heart means that it fails to pump blood around the body efficiently.
Researchers found that in the years after diagnosis, patients with heart failure had a 68% higher risk of developing cancer than those without a diagnosis of heart failure.
Unsurprisingly, the study also found that the people with heart failure who developed cancer were more likely to die early.
But even after taking many of these factors into account in their analysis, the researchers still found a statistically significant higher rate of cancer in heart failure patients.
There may have been other risk factors not taken into account, such as alcohol consumption, that could be an underlying cause behind the association, however.
The study ultimately raises more questions than it answers, and further research is required before any firm conclusions can be drawn.
If you are living with heart failure, worrying about studies such as this will not do either your heart or your cancer risk any good. Regular exercise and a healthy diet can help prevent both of these conditions.
Where did the story come from?
The study was carried out by researchers from the Mayo Clinic in the US, and the Rabin Medical Center and Tel Aviv University in Israel. It was funded by the US National Institutes of Health.
The study was published in the peer-reviewed Journal of the American College of Cardiology.
The Mail Online made two major errors in its coverage. First, it mistook "heart attack" for "heart failure". Heart attacks and heart failure are not the same, and many people who develop heart failure have no history of heart attacks.
Second, the headline claims that the stress and side effects of treatment for heart failure may trigger cancer. This claim is dangerously misleading. There is no evidence that treatment for heart failure can lead to cancer.
Researchers did discuss the possibility that heart failure medications may contribute to an increased cancer risk, but considered it "unlikely".
It is important that patients with heart failure take their prescribed medication, which can help stabilise the condition.
What kind of research was this?
This was a case-control study involving a group of patients newly diagnosed with heart failure matched to patients without heart failure. The researchers looked at the history of cancer in both groups.
They then followed those who did not have a diagnosis of cancer for an average of seven years in a cohort study looking at the risk of cancer.
In a case-control study, patients with a specific health problem are matched by age and sex to patients without that health problem to identify factors or outcomes that may be associated with the condition. This type of study cannot prove that such factors cause the condition or that the condition causes other outcomes.
The researchers say that heart failure is associated with a higher risk of illness and early death. Often there is no firm evidence that these types of cases have anything to do with heart failure itself and require further investigation.
Cancer is also a major cause of illness, but it is not known if cancer is associated with a risk of developing heart failure or vice versa. The researchers hypothesise that there may be a higher risk of cancer developing among heart failure patients.
What did the research involve?
The researchers recruited 961 patients who had been diagnosed with heart failure between 1979 and 2002. They recruited a control group from the general population without a diagnosis of heart failure who were individually matched to the heart failure patients by age, sex and index date (they did not have a diagnosis of heart failure up until the date the cases with heart failure were diagnosed).
In the first stage of the study, the researchers compared any previous history of cancer in the two groups using medical records. In the second stage, also using medical records, they followed 596 of these pairs of patients who had not been diagnosed with cancer by index date so they could compare the long-term risk of being diagnosed with cancer.
Follow-up lasted until death or the latest contact with a doctor, whichever came first. Types of cancer were classified according to the part of the body affected.
Non-melanoma skin cancers were excluded from the study, possibly because these types of cancers rarely prove fatal and are not associated with "traditional" risk factors for cancer.
Other data taken from the medical records was also recorded, such as a history of heart attack, diabetes, high blood pressure and high cholesterol. Body mass index was also calculated.
In their analysis, the researchers compared how many patients had already been diagnosed with cancer before the index date and how many patients went on to develop it afterwards. They adjusted their findings for factors that might affect the results (confounders), including weight, smoking and other illness. The researchers also looked at survival rates among patients, evaluating the risk of early death.
What were the basic results?
Researchers found that before the index date, 22% of heart failure cases and 23% of controls had a history of cancer (odds ratio [OR] 0.94, 95% confidence interval [CI] 0.75 to 1.17). During follow-up (7.7 years on average), 244 new cancer cases were identified.
Heart failure patients had a 68% higher risk of developing cancer (hazard ratio [HR] 1.68, 95% CI 1.13 to 2.50) even after adjusting for body mass index, smoking and comorbidities (other health conditions, such as high blood pressure).
The risk was similar for men and women. There was a trend toward a stronger association between heart failure and cancer among older patients, as well as among those diagnosed more recently.
Among people with heart failure, being diagnosed with cancer increased the risk of death (HR 1.56, 95% CI 1.22 to 1.99) compared with heart failure patients without cancer.
How did the researchers interpret the results?
The researchers conclude that heart failure patients are at an increased risk of cancer and that this risk appears to have increased over time.
Cancer was also found to increase the risk of death in heart failure patients compared with heart failure patients without cancer.
They say the study "underscores the importance of cancer surveillance in this population".
This study raises concerns about a possible association between heart failure and a higher risk of cancer. However, there is some uncertainty about the results. Further research is required looking at this important area.
It is possible that other factors called confounders influenced the results: both measured confounders, such as smoking, and unmeasured ones. Aside from smoking, it appears that researchers did not take account of other lifestyle measures that might be a risk factor for both diseases, such as diet and alcohol consumption.
The researchers did not report on the types of cancer patients had, which might have been useful in examining the association further.
As the researchers say, it is possible that there is an underlying risk factor for both heart failure and cancer – for instance, patients with a condition called chronic obstructive pulmonary disease have an increased risk for both heart failure and lung cancer.
Other mechanisms suggested by the researchers include the stress of chronic illness, or physiological factors associated with heart failure, such as inflammation, tissue death and hormonal changes.
But all of the above is firmly in the realm of speculation. As yet, it is unclear why people with heart failure appear to have an increased risk of cancer.