Heart attack or stroke may be an early sign of cancers, especially in older adults, say researchers.

The findings showed that the risk of having a heart attack and stroke jumped by 70 per cent in the year before cancer diagnosis. The risk was most acute in the month immediately before cancer diagnosis. 

Lung and colon cancers, as well as advanced-staged cancers, appear to be most strongly associated with an elevated risk of heart attack and stroke caused by blood clots in the arteries, according to a report published in the journal Blood.

"Our data shows there is an associated risk of ischemic stroke and heart attack that begins to increase in the five months before the cancer is officially diagnosed and peaks in the month just before," said lead author Babak Navi, Associate Professor at Cornell University in the US.

"These results suggest that cancer's effect on the clotting system may be what's predominantly driving the associated risk of heart attacks and stroke," Navi added.

Cancers can take months and sometimes years to develop and be diagnosed, and some cancers may be exerting biological effects on the body, especially thromboembolic activity, before they come to medical attention, he explained.

For the study, the team included 748,662 people (67 years and older) and looked at the risk of heart attack and stroke in those newly diagnosed with breast, lung, prostate, colorectal, bladder, non-Hodgkin lymphoma, uterine, pancreatic, and gastric cancers. 

When analysed separately, both heart attack and stroke risk were increased in the months before cancer diagnosis, although heart attack events were slightly more common than strokes. 

"If someone has a heart attack or stroke and there are any concerning signs for an undiagnosed malignancy, such as weight loss or unexplained anaemia, then perhaps a cancer screening should be considered," Navi said.