cervical smear

cervical smear Cervical cancer is a disease dreaded by women, but the advent of cervical smear tests has resulted in a significant reduction in the incidence of the disease, to the extent that, in the developed world at least, cervical cancer is justifiably now regarded as being largely preventable.

It was in 1949 that Papanicolaou and Traut published a paper which showed how cells shed from the cervix, popularly known as the ‘neck of the womb’, could be examined microscopically to diagnose cervical disease. This is known as exfoliative cytology and the name of the pioneer is sometimes retained in the colloquial term a ‘Pap smear’. Originally Papanicolaou and Traut intended exfoliative cytology as a test for early cancer, but it then became apparent that precancerous lesions could be detected by this means and treated much more easily and less radically than cancer. Such precancerous lesions, otherwise known as cervical intraepithelial neoplasia (CIN), may or may not become cancer over a number of years. By treating at this stage cancer can be prevented in almost 100% of cases. Programmes were initiated in British Columbia and Finland which proved beyond the doubt of most people that cervical screening saves lives. The key to these exemplary programmes was wide population coverage, the achievement of which is essential for their effectiveness. This has also been clearly demonstrated in the UK, where cervical screening was not sufficiently widespread to have an impact until the late 1980s. At that time the NHS introduced regular, computerized call and recall for all women between the ages of 20 and 65. As a result over 80% of the population is being regularly screened and there has been an undoubted reduction in deaths, from around 2000 deaths annually at the end of the 1980s to just over 1300 deaths in 1995.

A cervical smear is performed by exposing the part of the cervix which protrudes into the upper vagina. This is usually done by either a gynaecologist, a general practitioner, or a nurse practitioner. After exposing the cervix with a speculum, it is then firmly scraped with a wooden or plastic spatula around its entire surface and the exfoliated or surface cells which attach to the spatula are smeared on a glass slide and immediately covered with fixative which preserves the shape of the cells. The slides are then transported to a laboratory where they are stained to enable microscopic assessment.

Some smears are inadequate for examination and as such are labelled as ‘unsatisfactory’ requiring repeat smears. Five to ten per cent of smears will show some abnormality, but fewer than 1% abnormal smears are associated with cancer. Smears may show a spectrum of abnormality varying from very slight abnormalities, classified as borderline, to cell nuclear changes known as dyskaryosis (in the UK) or squamous epithelial lesion (in the US). Dyskaryotic changes are graded as mild, moderate, or severe (in the UK), or low grade or high grade (in the US). It must be appreciated that smears do not always accurately reflect underlying change: low grade smear changes may be associated with high grade CIN. On the other hand, although abnormal smears may suggest underlying precancer, often no significant change is present. Unfortunately many women do not realize this and immediately worry that they have cancer if the smear is not normal.

If the smear is normal, then it is repeated at whatever screening interval is advocated in that country, but it should be at least 5-yearly in the age 20–65. Very young women, even if sexually active, do not require to be screened below the age of 20 because the risk of cancer is extremely remote. Women over 65 who have been regularly screened are also at very low risk indeed of developing abnormal smears.

If the smear is mildly abnormal, a repeat smear in six months may be all that is required, but more severe changes require accurate diagnosis, and for this colposcopy should be performed. This involves looking directly at the cervix with a high magnification instrument; after wiping on acetic acid any abnormal areas become apparent. The area can be biopsied under direct vision and the tiny scrap of cervical tissue is looked at under the microscope by the pathologist. If precancer or cervical intraepithelial neoplasia is found, then the cervix is treated in such a way that the abnormal skin is destroyed or excised using techniques such as laser or diathermy. Fortunately this treatment has been shown not to affect a woman's ability to conceive or to have a normal delivery.

Abnormal smears are thought to be due in large part to infection of the cervix by some of the many types of human papilloma virus. Although other types of this virus cause warts, those that infect the cervix do not. The virus is probably transmitted in most cases by sexual intercourse and infection is found in around 5–10% of completely normal women. Scientific endeavour is currently aimed towards development of a vaccine to counter these virus infections.

Inevitably modern technology is beginning to have an impact on how we design our screening programmes. Computerized automated machines have been developed with the aim of reducing the need for cytoscreeners to look at large numbers of normal smears. In this way normal smears might be screened out and cytotechnicians could spend more time examining abnormal smears. These new technologies aimed at making screening more automated have not yet been fully proven, but it may well be that they will establish a role in the future. Another development is cytology in a liquid base to improve the quality of smears.

The absence of screening means that the major burden of cervical cancer is borne by women in impoverished countries, where it is the commonest cancer in women. This is compounded by a relative lack of treatment for the disease. It is to be hoped that improved health education, new technology, and rising affluence will enable many more women around the world to receive protection from cervical cancer by establishment of cervical cytology screening.

Henry C. Kitchener