Chapter 91: Cervical cancer screening

INTRODUCTION

Cervical cancer

Cervical cancer is the fourth most common cause of cancer death in women worldwide, especially in developing countries.¹ It is the most common cancer in women in Eastern and Middle Africa, and the 14th most common in Australian women.^1,2 Australia has the second lowest incidence of cervical cancer in the world as a result of the success of the National Cervical Screening Program introduced in 1991, which has halved its incidence.³

The most common cervical cancer is squamous cell carcinoma (SCC), accounting for 80% of cases. Adenocarcinoma is less common and more difficult to diagnose because it starts higher in the cervix. Cervical cancer almost exclusively occurs in women who have been sexually active, due to exposure to human papillomavirus (HPV). Other risk factors include smoking, use of combined oral contraception >5 years, immunosuppression and exposure to diethylstilboestrol in utero.⁴

Since the introduction of the human papillomavirus (HPV) vaccine in Australia in 2007, the incidence of low- and high-grade abnormalities has significantly reduced in vaccinated populations. Studies have revealed reductions as high as 45% for low-grade abnormalities and 85% for high-grade abnormalities.⁵ Recent modelling suggests that, with the tools available, elimination of cervical cancer in local populations is achievable within our lifetime.⁶

CERVICAL CANCER AND HUMAN PAPILLOMAVIRUS

⁷It is now well established that the primary cause of cervical cancer is human papillomavirus. There are approximately 200 different types of HPV, 40–50 of which specifically infect the anogenital area. These types are mainly spread by skin contact during sexual activity.

Of the genital HPV types, 15 are classified as ‘high risk’, as they are associated with anogenital cancer (including squamous and adenocarcinoma of the cervix). HPV 16 and 18 are responsible for around 70% of invasive cervical cancers and 50% of high-grade lesions.

Prior to immunisation, infection with HPV was common and mostly transient, with 80% of women being infected with at least one genital type of HPV in their lifetime without ever knowing it. Cervical cancer is a rare outcome of HPV infection. Most cervical HPV infections are cleared or suppressed by cell-mediated immunity within 1–2 years of exposure. Persistent infection of the cervix with a high-risk HPV is known to cause high-grade cervical changes that, if left untreated, can progress to cervical cancer. More than 99.7% of cervical cancers test positive for HPV DNA.⁸

Basic pathology

The focus of attention is ...