Many people in mid- and late life may be unfamiliar with common cancer symptoms such as unexplained coughing, bleeding, and persistent changes in bowel or bladder habits, suggests new research published Tuesday in the journal PLOS ONE.

In a questionnaire that asked about symptoms and their corresponding ailments, about 53 percent of 1,700 people surveyed reported that they had at least one red-flag cancer symptom during the previous three months— but only 2 percent said they thought cancer was a possible cause.

“Most people with potential warning symptoms don't have cancer, but some will and others may have other diseases that would benefit from early attention,” lead author Katriina Whitaker, senior research fellow at University College London, said in a news release. “That's why it's important that these symptoms are checked out, especially if they don't go away. But people could delay seeing a doctor if they don't acknowledge cancer as a possible cause.”

The survey listed 17 symptoms, including 10 widely known potential cancer warning signs, and was given to people ages 50 and older who were registered with three London general practice doctors. Study participants reported their symptoms and their suspected causes, as well as whether they thought their symptoms were serious and if they had consulted their doctor about them.

Researchers observed that survey respondents rarely credited potential signs of cancer to the disease— instead, they said they thought age, infection, arthritis, piles and cysts were more likely culprits.

"It's worrying that even the more obvious warning symptoms, such as unexplained lumps or changes to the appearance of a mole, were rarely attributed to cancer, although they are often well recognized in surveys that assess the public's knowledge of the disease,” Whitaker said. “Even when people thought warning symptoms might be serious, cancer didn't tend to spring to mind. This might be because people were frightened and reluctant to mention cancer, thought cancer wouldn't happen to them, or believed other causes were more likely."

Study participants were still able to identify the cancer red flags as more serious than the “non-alarm” symptoms, which include having a sore throat or feeling tired. Also, about 59 percent of those surveyed said they contacted a doctor about their “alarm” symptoms.

Sara Hiom, director of early diagnosis at Cancer Research UK, which funded the study, stressed the importance of cancer screening for early detection.

"Most cancers are picked up through people going to their [general practitioner] about symptoms, and this study indicates that opportunities for early diagnosis are being missed,” Hiom said in the news release. “Its results could help us find new ways of encouraging people with worrying symptoms to consider cancer as a possible cause and to get them checked out straightaway with a GP."

Researchers used the Cancer Awareness Measure system, based on warning signs from the Cancer Research UK website, as metrics for “alarm” and “non-alarm” cancer symptoms.

“Alarm” cancer symptoms included: unexplained cough or hoarseness; persistent change in bowel habits; persistent unexplained pain; persistent change in bladder habits; unexplained lump; a change in the appearance of a mole; a sore that does not heal; unexplained bleeding; unexplained weight loss; persistent difficulty swallowing.

“Non-alarm” symptoms included:  headache; shortness of breath; chest pain; feeling tired or having low energy; dizziness; feeling your heart pound or race; sore throat. According to the news release, these symptoms have varying levels of seriousness.