The Pap test is the most effective cancer-screening test in medical history and yet half a million women still die of cervical cancer each year. Only two events will improve those figures: The release of a new preventive vaccine or persuading more women to have a Pap test every two years. Peta Newbold reports.

Let's face it, women don't exactly hang out for a Pap test and anyone describing it as a pleasant experience wouldn't be telling the truth. But that doesn't alter the fact that facing the speculum and losing a few cells every two years could save your life.

It may seem obvious but cervical cancer is cancer of the cervix. That's the opening at the bottom of a woman's uterus, where it protrudes into the vagina and feels a little like the tip of the nose.

Cervical cancer is one of the most preventable cancers because the cells pass through a series of detectable changes before they become cancerous. If abnormal cells are spotted at an early stage, treatment can be given which will prevent these changes from developing into cancer.

In Australia a series of ongoing campaigns has been so successful that cervical cancer is now relatively uncommon. Even so it is still responsible for the deaths of more than 300 women each year and of those about 85 percent did not have the test every two years.

The Pap test: What should women expect?

Clothing has to be removed from the waist down but a sheet may be provided to make the woman feel more comfortable as she lies on her back or her side.

She will be asked to bend her knees and to open them. The practitioner will then gently insert an instrument called a speculum into the vagina. The speculum holds the walls of the vagina apart and allows a clear view of the cervix.

The cells are removed by a thin wooden spatula or small soft plastic brush, which is inserted through the speculum. This shouldn't be painful.

The practitioner smears the cells onto a glass slide, the speculum is removed and the examination is over.

The slide is sent to a pathology laboratory where the cells are examined under a microscope by a cytologist. The results are usually available within a week.

How accurate is it?

The Pap test is around 90 percent accurate. Some estimates put the number of false negatives as high as 10-20 percent . that is when a woman who actually has abnormal cells on her cervix is told her results are normal. However most cases of cervical cancer take up to 10 years to develop and any changes missed on one test are usually picked up two years later - long before they become a serious problem.

New developments in cervical screening.

The Pap test was developed in the 1920s by Dr George Papanicolaou and didn't alter much until the 1990s. Although nothing has yet replaced the need for direct examination of the cervix, it's thought a number of technological advances may improve its effectiveness.

Pathfinder.

The Pap test is taken in the conventional way. The pathfinder machine maps areas on a Pap test slide that have been examined by a cytologist and identifies which may be missed. Women are not charged extra for this.

PAPNET.

The Pap test is taken in the conventional way. After the Pap test has been examined by the cytologist it is sent away to be screened by a computerised microscope called PAPNET. There is an extra charge for this.

ThinPrep and Autocyte PREP.

The Pap test is taken in the conventional way. In addition to the slide, cells are placed in a liquid, which is also sent to the laboratory. A machine sucks up the cells from the liquid and deposits them in a thin, even layer onto the slide. This makes it easier to see than a conventional smear because blood, pus and other matter has been removed. There is an extra charge for this service.

Polarprobe.

The Polarprobe is a pen shaped device attached to a computer that is designed to give the clinician an instant result without taking cells from the cervix. The probe is placed on the surface of the cervix and the response from the electrodes and light source at the end of the probe is compared to a databank of cervical tissue types. It is still being developed and tested.

The Vaccine - the future?

The presence of genital human papilloma virus (HPV) or the genital wart virus has been found in almost all cases of cervical cancer. Therefore a vaccine designed to prevent the virus could have an enormous impact, particularly in parts of the world where the Pap test isn't available.

The papilloma virus prophylactic vaccine is currently being trialed all over the world and has been described as 'a major breakthrough'. Professor Ian Frazer leads one of the Australian trial clinics, at the Centre for Immunology and Cancer Research at the University of Queensland and he is more cautious.

He said "the definitive answer as to its efficacy won't be available for three years but all I can say is that it appears to have the same immunogenic effect in humans as it has proved to have in animals."

In the meantime we have the Pap test and Professor Frazer urges all women between the ages of 18 and 70 who have ever been sexually active to have one every two years.

He said, "Until the vaccine is proven to have a preventative effect the gold standard in the world at the moment for preventing cervical cancer is the Pap test. ThinPrep and PAPNET make that more effective but still 50 per cent of women are not regularly tested. So unless we can persuade more of them to have Pap tests nothing much will change."