Cervical Screening (Cervical Smear Test)

The annual incidence of cervical cancer in the UK was approximately 9.7 per 100,000 in 2003. 85-90% are squamous cell cancers, and approximately 15% are adenocarcinomas, which are more difficult to detect.¹
The cervical screening programme has not been without its critics, who have commented that the resulting reduction in mortality has been too small to justify the financial and psychosocial costs. However, cervical cancer rates in 2004 (2.8 per 100,000 females) were more than 60% lower than they were in 1975 (7.5 per 100,000 females). At least some of this decline has been due to the introduction of the NHS Cervical Screening Programme in 1987.² One analysis of mortality trends before and after the introduction of screening in the UK concluded that screening prevented an epidemic of cervical cancer, and that the programme is likely to prevent approximately 5000 deaths per year (in financial terms, a saving of about £36,000 per life).³

All women between the ages of 25-64 are eligible for screening.
As a result of evidence published in 2003, the NHS Screening Programme now offers screening at different intervals for different age groups. Women between 25-49 should be screened three yearly and women 50-64 five yearly. Women 65 and over only need to be screened if they have not had a smear since the age of 50, or have had a previously abnormal smear.
The latest published statistics (31st March 2004) showed that 80.6% of eligible women aged 25-64 resident in England had been screened at least once in the previous 5 years. This compared to 81.2% in 2003. In 213 of the 303 Primary Care Organisations the coverage was 80% or higher (226 in 2003).⁴

The Screening Process

A warmed speculum should be inserted vaginally to view the squamocolumnar junction of the cervix. Liquid-based cytology (LBC) is now the method of choice, as recommended by NICE. A brush is used rather than a spatula, which is rotated against the squamocolumnar junction (usually in the cervical canal). The end of the brush is then broken off into a container of preservative fluid, and sent to the laboratory. LBC is being rolled out nationally, and its availability currently depends upon local resources.¹
Older methods include the Papanicolaou (Pap) smear test which uses a brush or the Ayre spatula to sample the ectocervix by rotating it twice through 360 degrees. In both these methods, the material obtained is smeared onto a microscope slide, which is then sprayed with or immersed in a fixative solution prior to transporting to the laboratory.
The advantages of LBC over older methods is that reporting time is reduced, and there are less inadequate smears.¹

Cells are analysed to look for abnormalities in the appearance of the nucleus and other aspects of cell morphology (dyskaryosis). There is some lack of standardisation among laboratories, but basically one can expect to see one of the following results on a report:

• Negative - endocervical cells with normal nuclei are seen.
• Inadequate - the average national rate for inadequate smears is about 9%. Inadequate smears may be caused by insufficient or unsuitable material on the smear, inadequate fixation, poor spreading of the material on the slide, the presence of pus, blood or inflammatory exudate, or excessive cytolysis (this may be due to drying out of the smear, or hormone therapy).
• Borderline - this is reported in approximately 5% of smears. Cells are seen with abnormal nuclei, but the pathologist cannot say for certain they are indicative of dyskaryosis. Many patients revert to normal smears eventually. Human papilloma virus (HPV) infection is sometimes found in this group. Very few of these patients go on to develop cancer.
• Mild dyskaryosis - this occurs in approximately 5% of smears. Again, many women with this finding eventually revert to normal smears. HPV infection is a common association. Strictly speaking the cervical intraepithelial neoplasia (CIN) grading system should not be used on smears but on cervical biopsy material obtained during colposcopy. However, mild dyskaryosis usually equates to CIN1. Cancer is very unlikely.
• Moderate dyskaryosis - this usually equates to CIN2 and is seen in approximately 1% of samples. CIN2 is considered a pre-cancerous condition with an intermediate probability of developing into cancer.
• Severe dyskaryosis - this usually equates to CIN3. It occurs in about 0.5% of smears and is at the higher risk end of the cancer spectrum. About 0.1% of smears will show nuclear and other cellular changes suggestive of invasive carcinoma, sometimes referred to as carcinoma in situ.
• Glandular neoplasia - occasionally abnormalities of glandular cells are seen, suggestive of adenocarcinoma in situ, adenocarcinoma of the cervix, endometrial adenocarcinoma, or adenocarcinoma of an organ outside the uterus.

The limitations of Pap smears include variable sampling of cervical cells, poor transfer of cellular material onto the glass slide and sub-optimal preparation and fixation by the smear taker. It is hoped that the widespread introduction of LBC will help to reduce the inadequate rate. The inadequate is 9.1% with Pap smears compared to 1.6% with LBC. LBC is also 12% more sensitive than older methods.¹It should be remembered that cervical screening is but one strand of several approaches that should be taken in the continued battle against cervical cancer. Despite the screening programme, 3200 new cases of cervical cancer are seen each year. Some authorities view the condition as an entirely preventable disease and it has been suggested that each new case should be subject to a confidential enquiry in a similar manner to maternal deaths. Such an enquiry should address any failures of the screening process itself, contact tracing of HPV carriers, and access to secondary care.⁶