People surviving, or living with cancer may be more likely to die from a stroke than the general public, according to a major study that assessed data from more than 7 million patients who had been diagnosed with invasive forms of the disease. The researchers, including those from Pennsylvania State University in the US, used data gathered from the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) program in the US -- which includes information on cancer incidence, survival, treatment, and age and year of diagnosis of nearly 28 percent of the US population.
The study, published in the journal Nature Communications, revealed that people who have, or survived cancer are more than twice as likely to die of a stroke, with the risk increasing over the years.
The researchers said the SEER data contained information of more than 7.2 million patients who had been diagnosed with invasive cancer that has spread beyond the tissue in which it originally developed -- between 1992 and 2015.
Cancers of the breast, prostate, or parts of the large intestine were the most associated with fatal stroke, they said.
According to a bulletin by the World Health Organisation (WHO), cancer killed an estimated 9.6 million people in 2018, and a study published in the journal The Lancet in March noted that stroke accounted for more than 5 million deaths across the world.
The researchers said the two diseases could be related.
"Previous research has shown that most cancer patients aren't going to die of their cancer, they're going to die of something else," said study co-author Nicholas Zaorsky, assistant professor in radiation oncology at Pennsylvania State University.
"A stroke is one possibility. Our findings suggest that patients may benefit from a screening program to help prevent some of these early deaths from stroke, as well as help identify which patients we could target with those preventative efforts," Zaorsky said.
The researchers found that out of 7.5 million cancer patient data they analysed, more than 80,000 had died of a stroke, with men and women having equal chances of dying from a stroke.
The study noted that those diagnosed with cancer at a younger age had a higher chance of a fatal stroke.
Among those diagnosed with cancer before the age of 40, most strokes occurred in people treated for brain tumors and lymphomas, the researchers said.
In patients diagnosed with cancer before 40 years of age, they said, fatal strokes were most commonly associated with prostate, breast and colorectal cancer.
The researchers speculated this could be because many people diagnosed with cancer are in a "prothrombotic" state -- meaning they are more likely to form a blood clot.
"That blood clot may then go to the lungs and cause a pulmonary embolism, for example, or cause a stroke if it goes to the brain," Zaorsky said. "In general, it's an underlying theme and risk factor for a lot of cancer patients. And because certain cancers like those of the prostate, breast and colorectum are some of the most common cancers, that could also help explain that high association," he added.
The researchers said another reason for an increased stroke risk could be due to the weakening of blood vessels caused by chemotherapy or radiotherapy undergone by cancer patients.
"We can speculate that a subset of cancer patients are receiving chemotherapy or radiation treatments that may have a direct effect on the blood vessels to the brain and could increase stroke risk," said study co-author Brad Zacharia, an assistant professor of neurosurgery at Pennsylvania State University.
"This may be particularly true in patients with brain cancer," Zacharia said.