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

The following table outlines the protection against cancer provided by one smear:

Standard call and recall schedule

• First invitation for screening at age 25 in England (20 in rest of UK).
• Routine recall:
  • England: Routine 3 yearly recall between ages 25-49, then 5 yearly recall until aged 65.
  • Scotland: Routine 3 yearly recall from age 20 until aged 60.
  • Wales: Routine 3 yearly recall from age 20 until aged 65.
  • Northern Ireland: 5 year recall recall from age 20 until aged 65 (many GPs run their own recall at an interval of three years).
• Consider offering a smear to patients above the upper age limit, who have not been screened since age 50 or have had recent abnormal tests.

Notes

As a result of evidence published in 2003, the NHS Screening Programme in England 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.

Studies suggest that the effectiveness of this change in policy needs to be carefully monitored. One such study propounds that the exclusion of women aged 20-24 may lead to an increase in potentially treatable cervical intraepithelial neoplasia (CIN).⁵ Another concluded that a five year screening cycle in older women may increase non-compliance, resulting in increased costs without much benefit in terms of cancer prevention.⁶ A Belgian study found that the cost of sending a letter to non-compliant patients improved uptake and was cost-effective.⁷

A study of non-compliant women in Sweden concluded that the reasons women did not attend for smears was complex and affected by personal circumstances. Women who chose not to attend often felt healthy and cited other priorities. A negative body image, low self-esteem, feelings of discomfort when confronted with the gynaecological examination and fear of the results also influenced their non-attendance.⁸

The latest published statistics (31st March 2007) showed that 79.2% of eligible women aged 25-64 resident in England had been screened at least once in the previous 5 years. This compared to 79.5% in 2005. In 71 of the 152 Primary Care Organisations the coverage was 80% or higher (213 in 2004).⁹

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 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.¹

It 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.¹¹ One study looking at regular reviews of cervical screening status in patients with invasive cervical cancer concluded that such processes could be used to identify any problems in local screening services and act as a quality assurance mechanism.¹²

Computer assisted detection of cervical abnormalities may be possible in the future.

HPV vaccination was introduced in September 2008 for girls aged 12-13 and it will be many years before this programme has an effect on the incidence of cervical cancer.