Nearly 40% of people who fear they might have cancer delay visiting a doctor because they are worried about what they will find, according to new research.
Other sufferers are failing to recognise the symptoms of the disease at an early stage leading to thousands of avoidable deaths, Cancer Research UK said.
A report by the charity found that more than 75% of people asked to list the possible warning signs of cancer failed to mention pain, coughing or problems with bowels or bladder.
More than two-thirds of around 2,000 people surveyed in the UK also failed to list bleeding, while only one in four mentioned weight loss or mole changes.
Researches also found that a quarter of people who fear they may have the disease delay making a GP appointment because they are worried about wasting their doctor's time.
Statistics suggest 11,500 deaths could be avoided if the UK matched the best cancer survival rate in Europe.
But experts believe Britain is lagging behind because of its poor record in early diagnosis.
Professor Peter Johnson, Cancer Research UK's chief clinician, said: "If patients are diagnosed when the cancer is still in its early stages before it has had a chance to spread to other parts of the body it is more likely that treatment will be successful. That is why it is so important for people to be aware of things that might be early signs of cancer.
"Of course we are all frightened of hearing that we may have cancer. But people need to know that catching the disease early gives them much better odds of surviving it. The best precaution anyone can take is to be on the lookout for any changes in their bodies that seem unusual for them and to get them checked by a doctor."
The report, called Delay Kills, was funded by Tesco who have joined with the cancer charity to raise £10m to fund 32 early diagnosis research projects across the UK.