Researchers have highlighted the eight unexplained symptoms that are most closely linked to cancer.
The Keele University team also points to the age at which patients should be most concerned by the symptoms, which include blood in urine and anaemia.
The other symptoms are: rectal blood, coughing up blood, breast lump or mass, difficulty swallowing, post-menopausal bleeding and abnormal prostate tests, reports the BBC.
The figure for each symptom was calculated by combining the results of 25 previous studies.
They found that, if the patient was below the age of 55, there were only two signs, which reached the 'one-in-20' threshold.
These were a rectal prostate examination, which gave abnormal results, and a breast lump.
After 55, but only in men, there was evidence that difficulty swallowing could be a sign of oesophageal cancer, while blood in the urine was highlighted as a particular concern for men and women aged over 60.