The Pap smear isn't used to diagnose cancer, but it could be

Doctors can find it hard to diagnose cervical cancer in young women because the same symptoms, such as bleeding between periods or after sex, are common in women with genital infections or taking contraceptives. For decades the Pap smear has been used as a screening test to prevent women from getting cervical cancer. It is not used as a screening test in women younger than 25 because it isn’t effective at preventing cancer in this age group. But what if the Pap smear could be used to diagnose cervical cancer in young women?

In our latest research, published in the British Journal of General Practice, we found evidence that the Pap smear is an excellent test for finding cervical cancer in young women with symptoms. Currently, there isn’t a test that diagnoses cervical cancer once a woman has it. Doctors in primary care usually rely on looking at the cervix to check for cancer, but we know that this misses most cancers. Instead of just preventing cancer, this new-found role for the Pap smear could also help identify cervical cancer at an earlier, more treatable stage, which could save lives.

The Pap smear involves a doctor looking cells taken from the cervix under a microscope. For the purposes of cervical screening, the aim is to find abnormal cells so they can be removed before they become cervical cancer.

We looked at primary care medical records and cervical screening records for women aged 20 to 29. We compared Pap smear results from women with cervical cancer to results from women without cancer. We also looked at the symptoms women had using in-depth interviews and medical records.

Pap smear results are usually reported according to grade of abnormality. We found that over 90% of women with cervical cancer had a Pap smear result of moderate grade or worse. Using this as a cut-off point would mean that at least 90% of women with cervical cancer would be correctly identified by the Pap smear as a diagnostic test.

Importantly, very few women in the general population had the same test result, so women without cancer who go to their doctor with symptoms would not be unnecessarily worried by a false positive result.

Needle in a haystack

Cervical cancer in young women is rare – just 77 women aged under 25 are diagnosed with the disease in England each year. The main symptoms of cervical cancer are gynaecological, such as bleeding between periods or after sex, and vaginal discharge.

These symptoms are extremely common in young women, but for other less serious reasons, such as hormonal contraceptives and genital infections (for example, vaginal thrush or chlamydia). Unfortunately, for young women who do have cervical cancer, this means that doctors are very unlikely to suspect cancer.

Finding cervical cancer earlier is likely to have a big impact on young women. Treatment for advanced stage cervical cancer leaves women infertile. A test that diagnoses cervical cancer at an earlier stage could give women the chance to have a family in the future.

At the moment general practitioners (GPs) have no good way of knowing if a young woman with gynaecological symptoms has cervical cancer. The Pap smear as a diagnostic test for cancer would provide GPs with a powerful tool. GPs are likely to be enthusiastic about this repurpose of the Pap smear - a simple test that they are already familiar with.

A test for all women

Cervical screening doesn’t prevent all cervical cancers. Most cervical cancers are found when women go to their doctor with symptoms. Luckily it’s not just young women who could benefit from using the Pap smear as a diagnostic test.

In two related studies we showed that the Pap smear can be used to find cervical cancer in symptomatic women of all ages.

Despite its long-held success, the Pap smear will soon be replaced as the main cervical screening test by a new and better screening test. The new test detects the virus that causes cervical cancer - human papillomavirus. Now that a new use for the Pap smear has been found, though, perhaps it won’t be retired from service just yet. 

Anita Lim, Cancer epidemiologist, Queen Mary University of London

This article was originally published on The Conversation. Read the original article.