Refined Pap smear test more accurate

Sep 10 2008

Italian researchers have found that a new method of testing for cervical cancer is more accurate than a pap smear and also picks up more dangerous lesions.

The researchers from the Centre for Cancer Prevention in Turin combined the traditional test for the human papilloma virus (HPV) that causes cervical cancer, with another test which indicates specific cancer-causing activity in cells.

Dr. Guglielmo Ronco, a cancer epidemiologist, who led the study says a simple test for a protein called P16INK4A provided a biomarker showing cell changes that indicated a woman possibly has pre-cancerous lesions.

Dr. Ronco says this biomarker shows up any disruption by the HPV virus and as only a small minority of women who have an HPV infection actually develop cancer, the challenge is to establish which women have that higher risk.

Cervical cancer is the second most common type of cancer in women and each year an estimated 500,000 women are diagnosed with the disease and about 300,000 die from it, mostly in the developing world.

Vaccines such as Gardasil and Cervarix protect against some strains of the virus and many countries have screening programmes for the disease in the form of Pap smear tests.

However Pap smears produce too many false positives and some women get results which suggest they have potentially cancerous or pre-cancerous changes, when in fact they do not.

While an HPV test looks for the virus, a Pap smear involves doctors scraping cells from the cervix and examining them under a microscope for abnormalities that could indicate precancerous lesions.

Dr. Ronco says most HPV infections simply regress spontaneously without causing disease, which is the reason there are so many false positives.

For the study the researchers collected cervical cell samples from women who had already tested positive for the HPV virus, most of whom had already undergone an expensive colposcopy exam - a close examination of the cervix using a magnifying instrument.

But when the team tested for P16INK4A protein, in more than 1,100 of these women they found that it helped identified 88 percent of those who had the cancer-causing lesions with far fewer false positives, because the protein is more active in cervical-cancer cells.

Dr. Ronco says the refined test also identified 50% more of the dangerous lesions than Pap smears and required fewer women to be referred for colposcopy.

An online survey of 1,003 Australian women conducted for the Cancer Council, has revealed that one in 10 women, aged 28-34, has never had a Pap smear, which is recommended every two years - with more than half citing embarrassment as the main reason they delayed pap smears and 45% say they couldn't find the time.

The survey also revealed a certain amount of ignorance about Pap smears and many women were unaware that HPV caused cervical cancer and 41% did not know HPV can be sexually transmitted.

Experts have been both shocked and appalled at the level of ignorance regarding a potentially deadly cancer and say a sobering 45 Australian women are diagnosed with breast or gynaecological cancer each day and more than 4,100 die every year.

The Italian research is published in the journal Lancet Oncology.