The study, which features at the European Society for Medical Oncology (ESMO) 2017 Congress, held in Madrid, Spain, is the work of lead author Dr. Jacobo Rogado, medical oncology fellow at the Hospital de La Princesa in Madrid, and colleagues.
Dr. Rogado explains, "Postmortem studies have suggested that cancer can develop after a stroke, but the magnitude of this association has not been described."
He and his colleagues decided to carry out a study to probe the link and find out which factors might be involved.
A stroke is an attack in the brain that occurs when a clot interrupts or blocks the blood supply or a blood vessel bursts. The result is that cells are deprived of vital oxygen, without which they can die within minutes.
Each year in the United States, more than 795,000 people have a stroke. For most of them - around 610,000 - it is their first.
The new study concerns ischemic stroke, which occurs when blood supply in the brain is blocked or interrupted. This type is responsible for the vast majority of strokes (nearly 90 percent).
Screening could reduce cancer deaths
Cancer is a disease that develops when unchecked abnormal cells grow out of control and form growths, or tumors, that invade surrounding tissue.
Over time, cancer can reach a stage called metastasis. This occurs when cancer cells break away from the primary tumor - that is, where the cancer started - and travel through the blood or lymph system to form new, or metastatic, tumors in other organs and tissues. Most cancer deaths are caused by metastatic cancer.
More than 1.5 million people are diagnosed with cancer every year in the U.S., and more than 500,000 die of it. The number of new cases per year is expected to reach 2 million by 2020.
Research shows that vaccinations, healthy choices, and screening could prevent more than half of cancer deaths.
The new study relates to cancer screening, and if its findings are confirmed, the team suggests that stroke patients should perhaps be screened and followed for a while in case they have underlying cancer.
Excessive blood clotting
Blood clotting, or coagulation, is a normal response - following a wound, for example, in which proteins called fibrins and platelets come together to form a thickened mass of blood tissue.
The new findings support the idea that cancer can promote excessive blood clotting, or hypercoagulation.
"It has been suggested that cancer is a hypercoagulable state in which tumor cells activate the coagulation system," says Dr. Rogado.
For the new study, the team analyzed data on 381 patients referred from the emergency room to the stroke unit of the Hospital de La Princesa between January 2012 and December 2014. The patients had been followed for 18 months after receiving a stroke diagnosis.
The study's results showed that during the follow-up period, 7.6 percent of the stroke survivors (29 individuals) were diagnosed with cancer. This figure is nearly double the incidence in the general population (4.5 percent), note the authors.
The cancers that occurred most frequently in the stroke survivors were colon, lung, and prostate cancers.
The average time that elapsed between stroke and cancer diagnosis was 6 months, with nearly half (45 percent) of cancer diagnoses arising within the first half a year.
The team also found that nearly two thirds (62 percent) of the cancers diagnosed in the stroke survivors were either locally advanced or metastatic.
High blood levels of fibrinogen
Further analysis of the patients' medical records revealed that four factors were linked to cancer diagnosis: older age (77 years and above); having had a previous diagnosis for cancer; high blood levels of fibrinogen (above 450 milligrams per deciliter); and low levels of hemoglobin (under 13 grams per deciliter).
Dr. Rogado suggests that their findings indicate "that the cancer was already present when the stroke occurred but there were no symptoms."
The higher levels of fibrinogen - which is a protein that promotes blood coagulation - in the stroke patients that went on to develop cancer support the idea that the "prothrombotic effect of cancer contributed to the strokes," he adds.
"Stroke survivors should be followed clinically for the development of cancer in the 18 months after the diagnosis of stroke. This applies particularly to older patients who had cancer previously, or who have high fibrinogen or low levels of hemoglobin."
Dr. Jacobo Rogado
Dr. Fausto Roila, director of medical oncology at Santa Maria della Misericordia Hospital in Perugia, Italy - who was invited by the ESMO to comment on the findings - points to some important limitations of the research.
For example, there was no matched control group, and there is a problem with comparing cancer incidence in the study group with incidence in the general population. He explains, "The general population includes people of all ages, while the case population (patients with stroke) is primarily older patients."
"Therefore, further studies are needed before a firm association can be established between stroke and cancer," Dr. Roila concludes.