The researchers, led by Dr Cristina Bosetti (PhD), head of the Unit of Cancer Epidemiology at the Mario Negri Department of Oncology, Milan (Italy), found that regular use of aspirin, defined as taking at least one or two tablets a week, was associated with a significant reduction in the risk of developing all these cancers, apart from head and neck cancer.
Aspirin has been linked to a reduction in the risk of bowel cancer for some time, and other, smaller analyses have found associations with cancers of the oesophagus (the food pipe or gullet) and stomach.
This analysis looked at evidence from 113 observational studies investigating cancers in the general population published up to 2019, of which 45 studies were on bowel cancer and included 156,000 cases.
In addition to bowel cancer, the cancers investigated included those of the head and neck, oesophagus, stomach, the part of the stomach that connects to the oesophagus (gastric cardia), liver, gallbladder and bile ducts (hepato-biliary) and pancreas.
Specifically, aspirin use was linked to 27 per cent reduced risk of bowel cancer (45 studies), 33 per cent reduced risk of oesophageal cancer (13 studies), 39 per cent reduced risk of gastric cardia (ten studies), 36 per cent reduced risk of stomach cancer (14 studies), 38 per cent reduced risk of hepato-biliary cancers (five studies), and 22 per cent reduced risk of pancreatic cancer (15 studies).
Ten studies of head and neck cancer did not show a significant reduction in risk.
The senior author of the paper, Carlo La Vecchia (MD), Professor of Epidemiology at the School of Medicine, University of Milan, said: “There are about 175,000 deaths from bowel cancer predicted for 2020 in the EU, of which about 100,000 will be in people aged between 50 and 74.
“If we assume that regular use of aspirin increases from 25 per cent to 50 per cent in this age group, this would mean that between 5,000 to 7,000 deaths from bowel cancer and between 12,000 and 18,000 new cases could be avoided if further studies show that aspirin does indeed cause the reduction in cancer risk.
“Corresponding figures would be approximately 3,000 deaths each for oesophageal, stomach and pancreatic cancer, and 2,000 deaths from cancer of the liver.
“Given the unfavourable prognoses for these cancers, the number of new cases would be only slightly greater.”
The researchers also analysed the effect of aspirin dose and duration on bowel cancer.
They looked at low dose (100mg), regular (325mg) and high dose (500mg), combined with how many times a day, week or month it was taken.
Dr Bosetti said: “We found the risk of cancer was reduced with increased dose; an aspirin dose between 75 and 100mg a day was associated with a 10 per cent reduction in a person’s risk of developing cancer compared to people not taking aspirin; a dose of 325mg a day was associated with a 35 per cent reduction, and a dose of 500mg a day was associated with a 50 per cent reduction in risk.”