The incidence of cervical cancer in Singapore has been falling in recent years, and the latest figures (1998-2002) show the incidence to be 10.6 per 100,000 women per year. This makes it the 5 th commonest cancer in Singaporean women. Around 150 women are diagnosed with the disease and 50 die from it every year. Although the numbers may appear small on the face of it, the tragedy lies in the fact that there should be close to none at all.

One of the main aetiological factors for cervical cancer is infection with certain high-risk strains of the Human Papillomavirus (HPV). Clinical trials are underway evaluating the use of vaccines against certain subtypes of HPV to see if this will in turn reduce the incidence of cervical cancer. However, until such time that primary prevention is feasible, perhaps by means of these vaccines against HPV, screening remains the only practical way of reducing the incidence and mortality from cervical cancer.

The pre-invasive stages of cervical cancer can be easily detected, and treatment success is well over 90% thereby preventing progression to invasive disease. Cervical cancer is therefore largely but not entirely preventable with effective screening. In Singapore, the Health Promotion Board has embarked on a cervical cancer screening programme (CervicalScreen Singapore) in 2004. This programme targets sexually active women between the ages of 25 to 65 and encourages them to have a Pap smear every 3 years.

Diagnosis of Pre-Invasive Disease

If pre-invasive disease is suspected on a pap smear, the woman is referred for a Colposcopy examination. This is a relatively painless procedure in which the cervix is examined under magnification with a specialized microscope (Colposcope) with the aid of acetic acid (3-5%) and iodine solution (Figure 1).

By examining the degree of acetowhite change, blood vessels patterns, and other morphological features, the colposcopist is able to ascertain if any disease is present on the cervix and obtain biopsies if necessary for confirmation.

Pre-invasive squamous lesions are generally graded into 3 groups, cervical intraepithelial neoplasia (CIN) 1 to 3. There may also be pre-invasive and invasive (adenoarcinoma) glandular abnormalities in the cervix but these are not common.

Fig 2. Example of low grade Cervical Intraepithelial Neoplasia (CIN1). Note the pale degree of acetowhite change and irregular poorly defined borders.

Fig 3. Example of high-grade cervical intraepithelial neoplasia (CIN3). Note the dense acetowhite change with clearly defined borders and irregular dot-like blood vessel pattern (coarse punctuation).

Treatment of Pre-Invasive Lesions

It is important to understand the natural history of pre-invasive lesions as this helps to determine management of the disease. Low-grade lesions (CIN1) have a spontaneous regression rate of around 60% and only less than 1% will progress to cancer over the course of many years.

Therefore there is no consensus for the management of CIN1 and few clinicians nowadays would universally treat all CIN1 patients. An individualised approach is preferred, offering either immediate treatment, or follow up with repeat pap smears and colposcopy.

However, for high-grade lesions (CIN 2-3), the regression rate is much lower, around 30% and the progression rate to cancer is around 2% per year. Therefore, there is no place for the conservative management of high-grade lesions and all these women should be offered treatment.

Generally, two forms of treatments are available – either ablation or excision. In the former, the abnormal tissue is destroyed after biopsies have been taken. Methods of destruction include laser vaporisation, cryotherapy and electrodiathermy. The main drawback with these ablative methods of treatment is that there is no tissue specimen available for histology.

The commonest excisional method for treatment is the LEEP (Loop Electrodiathermy Excision Procedure). This uses a fine wire loop to remove a cone shaped piece of tissue from the cervix under local anaesthesia. Other excisional methods utilise the laser (laser cone biopsy) or a blade (knife cone biopsy). The excised specimen is sent for histology and both the grade of disease and the completeness of the excision to be determined.

 

Quek Swee Chong
Consultant
Gynaecological Oncology Unit
KK Women’s and Children’s Hospital

President
Society of Colposcopy & Cervical Pathology of Singapore